Internet DRAFT - draft-sriram-bgpsec-design-choices
draft-sriram-bgpsec-design-choices
Independent Submission K. Sriram, Ed.
Internet-Draft USA NIST
Intended status: Informational January 19, 2018
Expires: July 23, 2018
BGPsec Design Choices and Summary of Supporting Discussions
draft-sriram-bgpsec-design-choices-16
Abstract
This document captures the design rationale of the initial draft of
the BGPsec protocol specification. The designers needed to balance
many competing factors, and this document lists the decisions that
were made in favor of or against each design choice. This document
also presents brief summaries of the arguments that aided the
decision process. Where appropriate, this document also provides
brief notes on design decisions that changed as the specification was
reviewed and updated by the IETF SIDR working group, resulting in RFC
8205. These notes highlight the differences and provide pointers to
details and rationale about those design changes.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Creating Signatures and the Structure of BGPsec Update
Messages . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Origin Validation Using ROA . . . . . . . . . . . . . . . 4
2.2. Attributes Signed by an Originating AS . . . . . . . . . 5
2.3. Attributes Signed by an Upstream AS . . . . . . . . . . . 6
2.4. What Attributes Are Not Signed . . . . . . . . . . . . . 7
2.5. Receiving Router Actions . . . . . . . . . . . . . . . . 8
2.6. Prepending of ASes in AS Path . . . . . . . . . . . . . . 9
2.7. What RPKI Data Need be Included in Updates . . . . . . . 9
3. Withdrawal Protection . . . . . . . . . . . . . . . . . . . . 10
3.1. Withdrawals Not Signed . . . . . . . . . . . . . . . . . 10
3.2. Signature Expire Time for Withdrawal Protection (a.k.a.
Mitigation of Replay Attacks) . . . . . . . . . . . . . . 10
3.3. Should Route Expire Time be Communicated in a Separate
Message . . . . . . . . . . . . . . . . . . . . . . . . . 12
3.4. Effect of Expire-Time Updates in BGPsec on RFD . . . . . 13
4. Signature Algorithms and Router Keys . . . . . . . . . . . . 14
4.1. Signature Algorithms . . . . . . . . . . . . . . . . . . 14
4.2. Agility of Signature Algorithms . . . . . . . . . . . . . 15
4.3. Sequential Aggregate Signatures . . . . . . . . . . . . . 16
4.4. Protocol Extensibility . . . . . . . . . . . . . . . . . 17
4.5. Key Per Router (Rogue Router Problem) . . . . . . . . . . 18
4.6. Router ID . . . . . . . . . . . . . . . . . . . . . . . . 18
5. Optimizations and Resource Sizing . . . . . . . . . . . . . . 18
5.1. Update Packing and Repacking . . . . . . . . . . . . . . 19
5.2. Signature Per Prefix vs. Signature Per Update . . . . . . 19
5.3. Maximum BGPsec Update PDU Size . . . . . . . . . . . . . 20
5.4. Temporary Suspension of Attestations and Validations . . 21
6. Incremental Deployment and Negotiation of BGPsec . . . . . . 22
6.1. Downgrade Attacks . . . . . . . . . . . . . . . . . . . . 22
6.2. Inclusion of Address Family in Capability Advertisement . 22
6.3. Incremental Deployment: Capability Negotiation . . . . . 23
6.4. Partial Path Signing . . . . . . . . . . . . . . . . . . 23
6.5. Consideration of Stub ASes with Resource Constraints:
Encouraging Early Adoption . . . . . . . . . . . . . . . 24
6.6. Proxy Signing . . . . . . . . . . . . . . . . . . . . . . 25
6.7. Multiple Peering Sessions Between ASes . . . . . . . . . 26
7. Interaction of BGPsec with Common BGP Features . . . . . . . 26
7.1. Peer Groups . . . . . . . . . . . . . . . . . . . . . . . 26
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7.2. Communities . . . . . . . . . . . . . . . . . . . . . . . 27
7.3. Consideration of iBGP Speakers and Confederations . . . . 28
7.4. Consideration of Route Servers in IXPs . . . . . . . . . 28
7.5. Proxy Aggregation (a.k.a. AS_SETs) . . . . . . . . . . . 29
7.6. 4-Byte AS Numbers . . . . . . . . . . . . . . . . . . . . 30
8. BGPsec Validation . . . . . . . . . . . . . . . . . . . . . . 30
8.1. Sequence of BGPsec Validation Processing in a Receiver . 30
8.2. Signing and Forwarding Updates when Signatures Failed
Validation . . . . . . . . . . . . . . . . . . . . . . . 32
8.3. Enumeration of Error Conditions . . . . . . . . . . . . . 32
8.4. Procedure for Processing Unsigned Updates . . . . . . . . 33
8.5. Response to Syntactic Errors in Signatures and
Recommendation for Reaction . . . . . . . . . . . . . . . 34
8.6. Enumeration of Validation States . . . . . . . . . . . . 35
8.7. Mechanism for Transporting Validation State through iBGP 36
9. Operational Considerations . . . . . . . . . . . . . . . . . 38
9.1. Interworking with BGP Graceful Restart . . . . . . . . . 38
9.2. BCP Recommendations for Minimizing Churn: Certificate
Expiry/Revocation and Signature Expire Time . . . . . . . 39
9.3. Outsourcing Update Validation . . . . . . . . . . . . . . 39
9.4. New Hardware Capability . . . . . . . . . . . . . . . . . 40
9.5. Signed Peering Registrations . . . . . . . . . . . . . . 40
10. Security Considerations . . . . . . . . . . . . . . . . . . . 41
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 41
12. Informative References . . . . . . . . . . . . . . . . . . . 41
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 46
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 47
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 48
1. Introduction
The goal of BGPsec effort is to enhance the security of BGP by
enabling full AS path validation based on cryptographic principles.
Standards work on route origin validation based on a Resource
certificate PKI (RPKI) is already completed or nearing completion in
the IETF SIDR WG. The BGPsec effort is aimed at taking advantage of
the same RPKI infrastructure developed in the SIDR WG to add
cryptographic signatures to BGP updates, so that routers can perform
full AS path validation [RFC7132] [RFC7353] [RFC8205]. The BGPsec
protocol specification RFC was published recently [RFC8205]. The key
high-level design goals of the BGPsec protocol are as follow
[RFC7353]:
o Rigorous path validation for all announced prefixes; not merely
showing that a path is not impossible.
o Incremental deployment capability; no flag-day requirement for
global deployment.
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o Protection of AS paths only in inter-domain routing (eBGP); not
applicable to iBGP (or to IGPs).
o Aim for no increase in provider's data exposure (e.g., require no
disclosure of peering relations, etc.).
This document provides design justifications for the initial draft of
the BGPsec protocol specification [I-D.lepinski-bgpsec-protocol].
The designers needed to balance many competing factors, and this
document lists the decisions that were made in favor of or against
each design choice. This document also presents brief summaries of
the discussions that weighed in the pros and cons and aided the
decision process. Where appropriate, this document provides brief
notes (starting with "Note:") on design decisions that changed from
the approach taken in the initial draft of the BGPsec protocol
specification as the specification was reviewed and updated by the
IETF SIDR working group, resulting in [RFC8205]. The notes provide
pointers to the details and/or discussion about the design changes.
The design choices and discussions are presented under the following
eight broad categories (with many subtopics within each category):
(1) Creating Signatures and the Structure of BGPsec Update Messages,
(2) Withdrawal Protection, (3) Signature Algorithms and Router Keys,
(4) Optimizations and Resource Sizing, (5) Incremental Deployment and
Negotiation of BGPsec, (6) Interaction of BGPsec with Common BGP
Features, (7) BGPsec Validation, and (8) Operational Considerations.
2. Creating Signatures and the Structure of BGPsec Update Messages
2.1. Origin Validation Using ROA
2.1.1. Decision
Route origin validation using Route Origin Authorization (ROA)
[RFC6482] [RFC6811] is necessary and complements AS path attestation
based on signed updates. Thus, BGPsec design makes use of the origin
validation capability facilitated by the ROAs in RPKI.
Note: In the finalized BGPsec protocol specification [RFC8205],
BGPsec is synonymous with cryptographic AS path attestation. Origin
validation and BGPsec (path signatures) are the two key pieces of the
SIDR WG solution for BGP security.
2.1.2. Discussion
Route origin validation using RPKI constructs as developed in the
IETF SIDR WG is a necessary component of BGP security. It provides
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cryptographic validation that the first hop AS is authorized to
originate a route for the prefix in question.
2.2. Attributes Signed by an Originating AS
2.2.1. Decision
An originating AS will sign over the NLRI length, NLRI prefix, its
own AS number (ASN), the next ASN, the signature algorithm suite ID,
and a signature Expire Time (see Section 3.2) for the update. The
update signatures will be carried in a new optional, non-transitive
BGP attribute.
Note: The finalized BGPsec protocol specification [RFC8205] differs
from the above. There is no mention of a signature Expire Time field
in the BGPsec update in RFC 8205. Further, there are some additional
details concerning attributes signed by the origin AS that can be
found in Figure 8 in Section 4.2 of RFC 8205 [RFC8205]. In
particular, the signed data also includes the Address Family
Identifier (AFI) in RFC 8205. By adding the AFI in the data covered
by signature, a specific security concern was alleviated; see SIDR
list post [Mandelberg1] and the discussion thread that followed on
the topic. The AFI is obtained from the MP_REACH_NLRI attribute in
the BGPsec update. It is stated in Section 4.1 of RFC 8205 that
BGPsec update message MUST use the MP_REACH_NLRI attribute [RFC4760]
to encode the prefix.
2.2.2. Discussion
The next hop ASN is included in the data covered by the signature.
Without that the AS path cannot be secured; for example, it can be
shortened (by a MITM) without being detected.
It was decided that only the originating AS needs to insert a
signature Expire Time in the update, as it is the originator of the
route. The origin AS also will re-originate, i.e., beacon, the
update prior to the Expire Time of the advertisement (see
Section 3.2). (For an explanation of why upstream ASes do not insert
their respective signature Expire Times, please see Section 3.2.2.)
Note: Expire Time and beaconing were eventually replaced by router
key rollover. The BGPsec protocol [RFC8205] is expected to make use
of router key rollover to mitigate against replay attacks and
withdrawal suppression [I-D.ietf-sidrops-bgpsec-rollover]
[I-D.sriram-replay-protection-design-discussion].
It was decided that each signed update would include only one NLRI
prefix. If more than one NLRI prefix were included, and an upstream
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AS elected to propagate the advertisement for a subset of the
prefixes, then the signature(s) on the update would break (see
Section 5.1 and Section 5.2). If a mechanism were employed to
preserve prefixes that were dropped, this would reveal info to later
ASes that is not revealed in normal BGP operation. Thus, a tradeoff
was made to preserve the level of route info exposure that is
intrinsic to BGP over the performance hit implied by limiting each
update to carry only one prefix.
The signature data is carried in an optional, non-transitive BGP
attribute. The attribute is optional because this is the standard
mechanism available in BGP to propagate new types of data. It was
decided that the attribute should be non-transitive because of
concern about the impact of sending the (potentially large)
signatures to routers that don't understand them. Also, if a router
that doesn't understand BGPsec somehow gets a message with the
signatures attribute then it would be undesirable for that router to
forward the signatures to all its neighbors, especially those who do
not understand BGPsec and may choke if they receive many updates with
large optional BGP attributes. It is envisioned that BGPsec and
traditional BGP will co-exist while BGPsec is deployed incrementally.
2.3. Attributes Signed by an Upstream AS
In the context of BGPsec and throughout this document, an "upstream
AS" simply refers to an AS that is further along in an AS path
(origin AS being the nearest to a prefix). In principle, an AS that
is upstream from an originating AS would digitally sign the combined
information including the NLRI length, NLRI prefix, AS path, next
ASN, signature algorithm suite ID, and Expire Time. There are
multiple choices for what is signed by an upstream AS as follows.
Method 1: Signature protects the combination of NLRI length, NLRI
prefix, AS path, next ASN, signature algorithm suite ID, and Expire
Time; or Method 2: Signature protects just the combination of
previous signature (i.e., signature of the neighbor AS who forwarded
the update) and next ASN; or Method 3: Signature protects everything
that was received from preceding AS plus next (i.e., target) ASN;
thus, ASi signs over NLRI length, NLRI prefix, signature algorithm
suite ID, Expire Time, {ASi, AS(i-1), AS(i-2), ..., AS2, AS1},
AS(i+1)(i.e., next ASN), and {Sig(i-1), Sig(i-2), ..., Sig2, Sig1}.
Note: Please see the notes in Section 2.2.1 and Section 2.2.2 about
elimination of Expire Time field in the finalized BGPsec protocol
specification [RFC8205].
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2.3.1. Decision
It was decided that that Method 2 will be used. Please see
[I-D.lepinski-bgpsec-protocol] for additional protocol details and
syntax.
Note: The finalized BGPsec protocol specification [RFC8205]
essentially uses Method 3 (except for Expire Time). Additional
details concerning attributes signed by an upstream AS can be found
in Figure 8 in Section 4.2 of RFC 8205 [RFC8205]. The decision to go
with Method 3 (with suitable additions to the data signed) was
motivated by a security concern that was associated with Method 2;
see SIDR list post [Mandelberg2] and the discussion thread that
followed on the topic. Also, there is a strong rationale for the
sequence octets to be hashed (as shown in Figure 8 in Section 4.2 of
RFC 8205) and this sequencing of data is motivated by implementation
efficiency considerations; see SIDR list post [Borchert] for an
explanation.
2.3.2. Discussion
The rationale for this choice (Method 2) was as follows. Signatures
are performed over hash blocks. When the number of bytes to be
signed exceeds one hash block, then the remaining bytes will overflow
into a second hash block, which results in performance penalty. So
it is advantageous to minimize the number of bytes being hashed.
Also, an analysis of the three options noted above did not identify
any vulnerabilities associated with this approach.
2.4. What Attributes Are Not Signed
2.4.1. Decision
Any attributes other than those identified in Section 2.2 and
Section 2.3 are not signed. Examples of such attributes are
Community Attribute, NO-EXPORT Attribute, Local_Pref, etc.
2.4.2. Discussion
The above stated attributes that are not signed are viewed as local
(e.g., do not need to propagate beyond next hop) or lack clear
security needs. NO-EXPORT is sent over a secured next-hop and does
not need signing. BGPsec design should work with any transport layer
protections. It is well understood that the transport layer must be
protected hop by hop (if only to prevent malicious session
termination).
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2.5. Receiving Router Actions
2.5.1. Decision
The expected router actions on receipt of a signed update are
described by the following example. Consider an update that was
originated by AS1 with NLRI prefix p and has traversed the AS path
[AS(i-1) AS(i-2) .... AS2 AS1] before arriving at ASi. Let the
Expire Time (inserted by AS1) for the signature in this update be
denoted as Te. Let AlgID represent the ID of the signature algorithm
suite that is in use. The update is to be processed at ASi and
possibly forwarded to AS(i+1). Let the attestations (signatures)
inserted by each router in the AS path be denoted by Sig1, Sig2, ...,
Sig(i-2), and Sig(i-1) corresponding to AS1, AS2, ... , AS(i-2), and
AS(i-1), respectively.
The method (#2 in Section 2.3) selected for signing requires a
receiving router in ASi to perform the following actions:
o Validate the route origin pair (p, AS1) by performing a ROA match.
o Verify that Te is greater than the clock time at the router
performing these checks.
o Check Sig1 with inputs {NLRI length, p, AlgID, Te, AS1, AS2}.
o Check Sig2 with inputs {Sig1, AS3}.
o Check Sig3 with inputs {Sig2, AS4}.
o ...
o ...
o Check Sig(i-2) with inputs {Sig(i-3), AS(i-1)}.
o Check Sig(i-1) with inputs {Sig(i-2), ASi}.
o If the route that has been verified is selected as the best path
(for prefix p), then generate Sig(i) with inputs {Sig(i-1),
AS(i+1)}, and generate an update including Sig(i) to AS(i+1).
Note: The above description of BGPsec update validation and
forwarding differs in its details from the published BGPsec protocol
specification [RFC8205]. Please see Sections 4 and 5 of [RFC8205].
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2.5.2. Discussion
See Section 8.1 for suggestions regarding efficient sequencing of
BGPsec validation processing in a receiving router. Some or all the
validation actions may be performed by an off-board server (see
Section 9.3).
2.6. Prepending of ASes in AS Path
2.6.1. Decision
Prepending will be allowed. Prepending is defined as including more
than one instance of the AS number (ASN) of the router that is
signing the update.
Note: The finalized protocol specification uses a pCount field
associated with each AS in the path to indicate the number of
prepends for that AS (see Figure 5, Section 3.1 of [RFC8205]).
2.6.2. Discussion
The draft-00 version of the protocol specification calls for a
signature to be associated with each prepended AS. The optimization
of having just one signature for multiple prepended ASes will be
pursued later (i.e., beyond draft-00 specification). If such
optimization is used, a replication count would be included (in the
signed update) to specify how many times an AS was prepended.
2.7. What RPKI Data Need be Included in Updates
2.7.1. Decision
Concerning inclusion of RPKI data in an update, it was decided that
only the Subject Key Identifier (SKI) of the router cert must be
included in a signed update. This info identifies the router
certificate, based on the SKI generation criteria defined in
[RFC6487].
2.7.2. Discussion
It was discussed if each router public key certificate should be
included in a signed update. Inclusion of this information might be
helpful for routers that do not have access to RPKI servers or
temporarily lose connectivity to them. It is safe to assume that in
majority of network environments, intermittent connectivity would not
be a problem. So it is best to avoid this complexity because
majority of the use environments do not have connectivity
constraints. Because the SKI of a router certificate is a hash of
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the public key of that certificate, it suffices to select the public
key from that certificate. This design assumes that each BGPsec
router has access to a cache containing the relevant data from
(validated) router certificates.
3. Withdrawal Protection
3.1. Withdrawals Not Signed
3.1.1. Decision
Withdrawals are not signed.
3.1.2. Discussion
In the current BGP protocol, any AS can withdraw, at any time, any
prefix it previously announced. The rationale for not signing
withdrawals is that BGPsec assumes use of transport security between
neighboring BGPsec routers. Thus, no external entity can inject an
update that withdraws a route or replay a previously transmitted
update containing a withdrawal. Because the rationale for
withdrawing a route is not visible to a neighboring BGPsec router,
there are residual vulnerabilities associated with withdrawals. For
example, a router that advertised a (valid) route may fail to
withdraw that route when it is no longer viable. A router also might
re-advertise a route that it previously withdrew, before the route is
again viable. This latter vulnerability is mitigated by the Expire
Time value in an AS path signature (see Section 3.2).
Repeated withdrawals and announcements for a prefix can run up the
BGP RFD penalty and may result in unreachability for that prefix at
upstream routers. But what can the attacker gain from doing so?
This phenomenon is intrinsic to the design and operation of RFD.
3.2. Signature Expire Time for Withdrawal Protection (a.k.a.
Mitigation of Replay Attacks)
3.2.1. Decision
Note: As mentioned earlier in Section 2.2.2, the Expire Time approach
to mitigation of replay attacks and withdrawal suppression was
subsequently changed to an approach based on router key rollover
[I-D.ietf-sidrops-bgpsec-rollover]
[I-D.sriram-replay-protection-design-discussion].
Only the originating AS inserts a signature Expire Time in the
update; all other ASes along an AS path do not insert Expire Times
associated with their respective signatures. Further, the
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originating AS will re-originate a route sufficiently in advance of
the Expire Time of its signature so that other ASes along an AS path
will typically receive the re-originated route well ahead of the
current Expire Time for that route.
The duration of the signature Expire Time is recommended to be on the
order of days (preferably) but it may be on the order of hours (about
4 to 8 hours) in some cases, where extra replay protection is
perceived to be critical.
Each AS should stagger the Expire Time values in the routes it
originates. Re-origination will be done, say, at time Tb after
origination or the last re-origination, where Tb will equal a certain
percentage of the Expire Time, Te (for example, Tb = 0.75 x Te). The
percentage will be configurable and additional guidance can be
provided via an operational considerations document later. Further,
the actual re-origination time should to be jittered with a uniform
random distribution over a short interval {Tb1, Tb2} centered at Tb.
It is also recommended that a receiving BGPsec router should detect
if the only attribute change in an announcement (relative to the
current best path) is the expire time (besides, of course, the
signatures). In that case, assuming that the update is found valid,
the route processor should not re-announce the route to non-BGPsec
peers. (It should sign and re-announce the route to only BGPsec
speakers.) This procedure will reduce BGP chattiness for the non-
BGPsec border routers.
3.2.2. Discussion
Mitigation of BGPsec update replay attacks can be thought of as
protection against malicious re-advertisement of withdrawn routes.
If each AS along a path were to insert its own signature Expire Time,
then there would be much additional BGP chattiness and increase in
BGP processing load due to the need to detect and react to multiple
(possibly redundant) signature Expire Times. Furthermore, there
would be no extra benefit from the point of view of mitigation of
replay attacks as compared to having a single Expire Time
corresponding to the signature of the originating AS.
The recommended Expire Time value is on the order of days but 4 to 8
hours may used in some cases on the basis of perceived need for extra
protection from replay attacks. Thus, different ASes may choose
different values based on the perceived need to protect against
malicious route replays. (A shorter Expire Time reduces the window
during which an AS can maliciously replay the route. However,
shorter Expire Time values cause routes to be refreshed more often,
and thus causes more BGP chatter.) Even a 4 hours duration seems
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long enough to keep the re-origination workload manageable. For
example, if 500K routes are re-originated every 4 hours, it amounts
to an increase in BGP update load of 35 updates per second; this can
be considered reasonable. However, further analysis is needed to
confirm these recommendations.
It was stated above that originating AS will re-originate a route
sufficiently in advance of its Expire Time. What is considered
sufficiently in advance? For this, modeling should be performed to
determine the 95th-percentile convergence time of update propagation
in BGPsec enabled Internet.
Each BGPsec router should stagger the Expire Time values in the
updates it originates, especially during table dumps to a neighbor or
during its own recovery from a BGP session failure. By doing this,
the re-origination (i.e., beaconing) workload at the router will be
dispersed.
3.3. Should Route Expire Time be Communicated in a Separate Message
3.3.1. Decision
The idea of sending a new signature expire time in a special message
(rather than re-transmitting the entire update with signatures) was
considered. However, it was decided not to do this. Re-origination
to communicate a new signature Expire Time will be done by
propagation of a normal update message; no special type of message
will be required.
3.3.2. Discussion
It was suggested that if re-beaconing of signature Expire Time is
carried in a separate special message, then update processing load
may be reduced. But it was recognized that such re-beaconing message
necessarily entails AS path and prefix information, and hence cannot
be separated from the update.
It was observed that at the edge of the Internet, there are frequent
updates that may result from simple situations like BGP session being
switched from one interface to another (e.g., from primary to backup)
between two peering ASes (e.g., customer and provider). With
traditional BGP, these updates do not propagate beyond the two ASes
involved. But with BGPsec, the customer AS will put in a new
signature Expire Time each time such an event happens, and hence the
update will need to propagate throughout the Internet (limited only
by best path selection process). It was accepted that this cost of
added churn will be unavoidable.
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3.4. Effect of Expire-Time Updates in BGPsec on RFD
3.4.1. Decision
With regard to the Route Flap Damping (RFD) protocol
[RFC2439][JunOS][CiscoIOS], no differential treatment is required for
Expire-Time triggered (re-beaconed) BGPsec updates.
However, it was noted that it would be preferable if these updates
did not cause route churn (and perhaps not even require any RFD
related processing), since they are identical except for the change
in the Expire Time value. The way this can be accomplished is by not
assigning RFD penalty to Expire-Time triggered updates. If the
community agrees, this could be accommodated, but a change to the
BGP-RFD protocol specification will be required.
3.4.2. Discussion
Summary:
The decision is supported by the following observations: (1) Expire
Time-triggered updates are generally not preceded by withdrawals, and
hence the path hunting and associated RFD exacerbation
[Mao02][RIPE580] problems are not anticipated; (2) Such updates would
not normally change the best path (unless another concurrent event
impacts the best path); (3) Expire Time-triggered updates would have
negligible impact on RFD penalty accumulation because the re-
advertisement interval is much longer relative to the half-time of
decay of RFD penalty. Elaborating further on reason #3 above, it may
be noted that the re-advertisements (i.e., beacons) of a route for a
given address prefix from a given peer will be received at intervals
of a few or several hours (see Section 3.2). During that time
period, any incremental contribution to RFD penalty due to a Expire
Time-triggered update would decay sufficiently to have negligible (if
any) impact on damping the address prefix in consideration.
Additional details of this analysis and justification can be found
below.
Further Details of the Analysis and Justification:
The frequency with which RFD penalty increments may be triggered for
a given prefix from a given peer is the same as the re-beaconing
frequency for that prefix from its origin AS. The re-beaconing
frequency is on the order of once every few or several hours (see
Section 3.2). The incremental RFD penalty assigned to a prefix due
to a re-beaconed update varies depending on the implementation. For
example, it appears that JunOS implementation [JunOS] would assign a
penalty of 1000 or 500 depending on whether the re-beaconed update is
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regarded as a re-advertisement or an attribute change, respectively.
Normally, a re-beaconed update would be treated as a case of
attribute change. The Cisco implementation [CiscoIOS] on the other
hand assigns an RFD penalty only in the case of an actual flap (i.e.,
a route is available, then unavailable, or vice versa). So it
appears that Cisco implementation of RFD would not assign any penalty
for a re-beaconed update (i.e., a route was already advertised
previously; not withdrawn; and the re-beaconed update is merely
updating the expire time attribute). Even if one assumes that an RFD
penalty of 500 is assigned (corresponding to attribute change in
JunOS RFD implementation), it can be illustrated that the incremental
affect it would have on damping the prefix in consideration would be
negligible. The reason for this is as follows. The half-time of RFD
penalty decay is normally set to 15 minutes, whereas the re-beaconing
frequency is on the order of once every few or several hours. An
incremental penalty of 500 would decay to 31.25 in one hour; 0.12 in
two hours; 3x10^(-5) in three hours. It may also be noted that the
threshold for route suppression is 3000 in JunOS and 2000 in Cisco
IOS. Based on the foregoing analysis, it may be concluded that
routine re-beaconing by itself would not result in RFD suppression of
routes in the BGPsec protocol.
4. Signature Algorithms and Router Keys
4.1. Signature Algorithms
4.1.1. Decision
Initially, ECDSA with Curve P-256 and SHA-256 will be used for
generating BGPsec path signatures. One other signature algorithm,
e.g., RSA-2048 will also be used during prototyping and testing. The
use of a second signature algorithm is needed to verify the ability
of the BGPsec implementations to change from a current algorithm to
the next algorithm.
Note: The BGPsec cryptographic algorithms document [RFC8208]
specifies only ECDSA with Curve P-256 and SHA-256.
4.1.2. Discussion
Initially, choice of RSA-2048 algorithm for BGPsec update signatures
was considered because it is being used ubiquitously in the RPKI
system. However, the use of ECDSA P-256 algorithm was decided
because it yields a smaller signature size, and hence the update size
and in turn the RIB size needed in BGPsec routers would be much
smaller [RIB_size].
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Testing with two different signature algorithms (e.g., ECDSA P-256
and RSA-2048) for transition from one to the other will increase
confidence in prototype implementations.
For Elliptic Curve Cryptography (ECC) algorithms, according to
[RFC6090], optimizations and specialized algorithms (e.g., for speed-
ups) have active IPR, but the basic (unoptimized) algorithms do not
have IPR encumbrances.
Note: Recently, even open source implementations have incorporated
certain cryptographic optimizations and demonstrated significant
performance speedup [Gueron]. Researchers continue to devote
significant efforts to demonstrate substantial speedup for ECDSA as
part of BGPsec implementations [Mehmet1] [Mehmet2].
4.2. Agility of Signature Algorithms
4.2.1. Decision
During the transition period from one algorithm, i.e., current
algorithm, to the next (new) algorithm, the updates will carry two
sets of signatures (i.e., two Signature-List Blocks), one
corresponding to each algorithm. Each Signature-List Block will be
preceded by its type-length field and an algorithm-suite identifier.
A BGPsec speaker that has been upgraded to handle the new algorithm
should validate both Signature-List Blocks, and then add its
corresponding signature to each Signature-List Block for forwarding
the update to the next AS. A BGPsec speaker that has not been
upgraded to handle the new algorithm will strip off the Signature-
List Block of the new algorithm, and forward the update after adding
its own sig to the Signature-List Block of the current algorithm.
It was decided that there will be at most two Signature-List Blocks
per update.
Note: Signature-List Block is Signature_Block in RFC 8205. The
algorithm agility scheme described in the published BGPsec protocol
specification is consistent with the above; see Section 6.1 of
[RFC8205].
4.2.2. Discussion
A length field in the Signature-List Block allows for delineation of
the two signature blocks. Hence, a BGPsec router that doesn't know
about a particular algorithm suite (and hence doesn't know how long
signatures were for that algorithm suite) could still skip over the
corresponding Signature-List Block when parsing the message.
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The overlap period between the two algorithms is expected to last two
to four years. The RIB memory and cryptographic processing capacity
will have to be sized to cope with such overlap periods when updates
would contain two sets of signatures [RIB_size].
The lifetime of a signature algorithm is anticipated to be much
longer than the duration of a transition period from current to new
algorithm. It is fully expected that all ASes will have converted to
the required new algorithm within a certain amount of time that is
much shorter than the interval in which a subsequent newer algorithm
may be investigated and standardized for BGPsec. Hence, the need for
more than two Signature-List Blocks per update is not envisioned.
4.3. Sequential Aggregate Signatures
4.3.1. Decision
There is currently weak or no support for the Sequential Aggregate
Signature (SAS) approach. Please see in the discussion section below
for a brief description of what SAS is and what its pros and cons
are.
4.3.2. Discussion
In Sequential Aggregate Signature (SAS) method, there would be only
one (aggregated) signature per signature block, irrespective of the
number of AS hops. For example, ASn (nth AS) takes as input the
signatures of all previous ASes [AS1, ..., AS(n-1)] and produces a
single composite signature. This composite signature has the
property that a recipient who has the public keys for AS1, ..., ASn
can verify (using only the single composite signature) that all of
the ASes actually signed the message. SAS could potentially result
in savings in bandwidth, PDU size, and maybe in RIB size but the
signature generation and validation costs will be higher as compared
to one signature per AS hop.
SAS schemes exist in the literature, typically based on RSA or
equivalent. For SAS with RSA and for the cryptographic strength
needed for BGPsec signatures, a 2048-bit signature size (RSA-2048)
would be required. However, without SAS, ECDSA with 512-bit
signature (256-bit key) would suffice for equivalent cryptographic
strength. The larger signature size of RSA used with SAS undermines
the advantages of SAS, because the average hop count, i.e., number of
ASes, for a route is about 3.8. In the end, it may turn out that SAS
has more complexity and does not provide sufficient savings in PDU
size or RIB size to merit its use. Further exploration of this is
needed to better understand SAS properties and applicability for
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BGPsec. There is also a concern that SAS is not a time-tested
cryptographic technique and thus its adoption is potentially risky.
4.4. Protocol Extensibility
There is a clearly a need to specify a transition path from a current
protocol specification to a new version. When changes to the
processing of the BGPsec path signatures are required, that will
require a new version of BGPsec. Examples of this include changes to
the data that is protected by the BGPsec signatures or adoption of a
signature algorithm in which the number of signatures in the
signature block may not correspond to one signature per AS in the AS-
PATH (e.g., aggregate signatures).
4.4.1. Decision
The protocol-version transition mechanism here is analogous to the
algorithm transition discussed in Section 4.2. During the transition
period from one protocol version (i.e., current version) to the next
(new) version, updates will carry two sets of signatures (i.e., two
Signature-List Blocks), one corresponding to each version. A
protocol-version identifier is associated with each Signature-List
Block. Hence, each Signature-List Block will be preceded by its
type-length field and a protocol-version identifier. A BGPsec
speaker that has been upgraded to handle the new version should
validate both Signature-List Blocks, and then add its corresponding
signature to each Signature-List Block for forwarding the update to
the next AS. A BGPsec speaker that has not been upgraded to handle
the new protocol version will strip off the Signature-List Block of
the new version, and forward the update with an attachment of its own
signature to the Signature-List Block of the current version.
Note: Signature-List Block is Signature_Block in RFC 8205. The
details of protocol extensibility (i.e., transition to a new version
of BGPsec) in the published BGPsec protocol specification (see
Section 6.3 in [RFC8205]) differ somewhat from the above. In
particular, the protocol-version identifier is not part of the BGPsec
update. Instead, it is negotiated during BGPsec capability exchange
during the BGPsec session negotiation.
4.4.2. Discussion
In the case that change to BGPsec is deemed desirable, it is expected
that a subsequent version of BGPsec would be created and that this
version of BGPsec would specify a new BGP Path Attribute, let's call
it BGPsec_PATH_SIG_TWO, which is designed to accommodate the desired
changes to BGPsec. At this point a transition would begin which is
analogous to the algorithm transition discussed in Section 4.2.
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During the transition period, all BGPsec speakers will simultaneously
include both the BGPsec_Path_Signatures (current) attribute and the
new BGPsec_PATH_SIG_TWO attribute. Once the transition is complete,
the use of BGPsec_Path_Signatures could then be deprecated, at which
point BGPsec speakers will include only the new BGPsec_PATH_SIG_TWO
attribute. Such a process could facilitate a transition to a new
BGPsec semantics in a backwards compatible fashion.
4.5. Key Per Router (Rogue Router Problem)
4.5.1. Decision
Within each AS, each individual BGPsec router can have a unique pair
of private and public keys [RFC8207].
4.5.2. Discussion
Given unique key pair per router, if a router is compromised, its key
pair can be revoked independently, without disrupting the other
routers in the AS. Each per-router key-pair will be represented in
an end-entity certificate issued under the CA cert of the AS. The
Subject Key Identifier (SKI) in the signature points to the router
certificate (and thus the unique public key) of the router that
affixed its signature, so that a validating router can reliably
identify the public key to use for signature verification.
4.6. Router ID
4.6.1. Decision
The router certificate Subject name will be the string "router"
followed by a decimal representation of a 4-byte AS number followed
by the router ID. See the current RFCs for preferred standard
textual representations for 4-byte ASNs [RFC5396] and router IDs
[RFC6891].
4.6.2. Discussion
Every X.509 certificate requires a Subject name. The stylized
Subject name adopted here is intended to facilitate debugging, by
including the ASN and router ID.
5. Optimizations and Resource Sizing
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5.1. Update Packing and Repacking
With traditional BGP protocol [RFC4271], an originating BGP router
normally packs multiple prefix announcements into one update if the
prefixes all share the same BGP attributes. When an upstream BGP
router forwards eBGP updates to its peers, it can also pack multiple
prefixes (based on shared AS path and attributes) into one update.
The update propagated by the upstream BGP router may include only a
subset of the prefixes that were packed in a received update.
5.1.1. Decision
Each update contains exactly one prefix. This avoids the complexity
that would be otherwise inevitable if the origin had packed and
signed multiple prefixes in an update and an upstream AS decided to
propagate an update containing only a subset of the prefixes in that
update. BGPsec recommendation regarding packing and repacking may be
be revisited when optimizations are considered in the future.
5.1.2. Discussion
Currently, with traditional BGP, there are, on average, approximately
4 prefixes announced per update [RIB_size]. So the number of BGP
updates (carrying announcements) is about 4 times fewer, on average,
as compared to the number of prefixes announced.
The current decision is to include only one prefix per secured update
(see Section 2.2 and Section 2.3). When optimizations are considered
in the future, the possibility of packing multiple prefixes into an
update can be considered. (Please see Section 5.2 for a discussion
of signature per prefix vs. signature per update.) Repacking could
be performed if signatures were generated on a per prefix basis.
However, one problem regarding this approach, i.e., multiple prefixes
in a BGP update but with a separate signature for each prefix, is
that the resulting BGP update violates the basic definition of a BGP
update. That is because the different prefixes will have different
signature and expire-time attributes, while a BGP update (by
definition) must have the same set of shared attributes for all
prefixes it carries.
5.2. Signature Per Prefix vs. Signature Per Update
5.2.1. Decision
The initial design calls for including exactly one prefix per update,
hence there is only one signature in each secured update (modulo
algorithm transition conditions). Optimizations will be examined
later.
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5.2.2. Discussion
Some notes to assist in future optimization discussions: In the
general case of one signature per update, multiple prefixes may be
signed with one signature together with their shared AS path, next
ASN, and Expire Time. If signature per update is used, then there
are potentially savings in update PDU size as well as RIB memory
size. But if there are any changes made to the announced prefix set
along the AS path, then the AS where the change occurs would need to
insert an Explicit Path Attribute (EPA)[I-D.draft-clynn-s-bgp]. The
EPA conveys information regarding what the prefix set contained prior
to the change. There would be one EPA for each AS that made such a
modification, and there would be a way to associate each EPA with its
corresponding AS. This enables an upstream AS to be able to know and
to verify what was announced and signed by prior ASes in the AS path
(in spite of changes made to the announced prefix set along the way).
The EPA adds complexity to processing (signature generation and
validation), further increases the size of updates and, thus of the
RIB, and exposes data to downstream ASes that would not otherwise be
exposed. Not all the pros and cons of packing and repacking in the
context of signature per prefix vs. signature per update (with
packing) have been evaluated. But the current recommendation is for
having only one prefix per update (no packing); so there is no need
for the EPA attribute.
5.3. Maximum BGPsec Update PDU Size
The current BGP update message PDU size is limited to 4096 bytes
[RFC4271]. The question was raised if BGPsec would require a larger
update PDU size.
5.3.1. Decision
The current thinking is that the max PDU size should be increased to
64 KB [I-D.ietf-idr-bgp-extended-messages] so that there is
sufficient room to accommodate two signature-list blocks (i.e., one
block with a current algorithm and another block with a new signature
algorithm during a future transition period) for long AS paths.
Note: RFC 8205 states the following: "All BGPsec update messages MUST
conform to BGP's maximum message size. If the resulting message
exceeds the maximum message size, then the guidelines in Section 9.2
of RFC 4271 [RFC4271] MUST be followed."
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5.3.2. Discussion
The current maximum message size for BGP updates is 4096 octets.
There is effort underway in the IETF to extend it to a larger size
[I-D.ietf-idr-bgp-extended-messages]. BGPsec will conform to
whatever maximum message size that is available for BGP while
adhering to the guidelines in Section 9.2 of RFC 4271 [RFC4271].
Note: Estimates for the average and maximum sizes anticipated for
BGPsec update messages are provided in [MsgSize].
5.4. Temporary Suspension of Attestations and Validations
5.4.1. Decision
If a BGPsec-capable router needs to temporarily suspend/defer signing
and/or validation of BGPsec updates during periods of route processor
overload, the router may do so even though such suspension/deferment
is not desirable. The specification does not forbid that. Following
any temporary suspension, the router should subsequently send signed
updates corresponding to the updates for which validation and signing
were skipped. The router also may choose to skip only validation but
still sign and forward updates during periods of congestion.
5.4.2. Discussion
In some situations, a BGPsec router may be unable to keep up with the
workload of performing signing and/or validation. This can happen,
for example, during BGP session recovery when a router has to send
the entire routing table to a recovering router in a neighboring AS
(see [CPUworkload]). So it is possible that a BGPsec router
temporarily pauses performing validation or signing of updates. When
the work load eases, the BGPsec router should clear the validation or
signing backlog, and send signed updates corresponding to the updates
for which validation and signing were skipped. During periods of
overload, the router may simply send unsigned updates (with
signatures dropped), or may sign and forward the updates with
signatures (even though the router itself has not yet verified the
signatures it received).
A BGPsec-capable AS may request (out-of-band) a BGPsec-capable peer
AS never to downgrade a signed update to an unsigned update.
However, in partial deployment scenarios, it is not possible for a
BGPsec router to require a BGPsec-capable eBGP peer to send only
signed updates, except for prefixes originated by the peer's AS.
Note: If BGPsec has not been negotiated with a peer, then a BGPsec
router forwards only unsigned updates to that peer. For this, the
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sending router follows the reconstruction procedure of Section 4.4 in
[RFC8205] to generate an AS_PATH attribute corresponding to the
BGPsec_PATH attribute in a received signed update. If the above
mentioned temporary suspension is ever applied, then the same AS_PATH
reconstruction procedure should be utilized.
6. Incremental Deployment and Negotiation of BGPsec
6.1. Downgrade Attacks
6.1.1. Decision
No attempt will be made in BGPsec design to prevent downgrade
attacks, i.e., a BGPsec-capable router sending unsigned updates when
it is capable of sending signed updates.
6.1.2. Discussion
BGPsec allows routers to temporarily suspend signing updates (see
Section 5.4). Therefore, it would be contradictory if we were to try
to incorporate in the BGPsec protocol a way to detect and reject
downgrade attacks. One proposed way for detecting downgrade attacks
was considered, based on signed peering registrations (see
Section 9.5).
6.2. Inclusion of Address Family in Capability Advertisement
6.2.1. Decision
It was decided that during capability negotiation, the address family
for which the BGPsec speaker is advertising support for BGPsec will
be shared using the Address Family Identifier (AFI). Initially, two
address families would be included, namely, IPv4 and IPv6. BGPsec
for use with other address families may be specified in the future.
Simultaneous use of the two (i.e., IPv4 and IPv6) address families
for the same BGPsec session will require that the BGPsec speaker must
include two instances of this capability (one for each address
family) during BGPsec capability negotiation.
6.2.2. Discussion
If new address families are supported in the future, they will be
added in future versions of the specification. A comment was made
that too many version numbers are bad for interoperability. Re-
negotiation on the fly to add a new address family (i.e., without
changeover to new version number) is desirable.
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6.3. Incremental Deployment: Capability Negotiation
6.3.1. Decision
BGPsec will be incrementally deployable. BGPsec routers will use
capability negotiation to agree to run BGPsec between them. If a
BGPsec router's peer does not agree to run BGPsec, then the BGPsec
router will run only traditional BGP with that peer, i.e., it will
not send BGPsec (i.e., signed) updates to the peer.
Note: See Section 7.9 of [RFC8205] for a discussion of incremental/
partial deployment considerations. Also, see Section 6 of [RFC8207]
where it is described that edge sites (stub ASes) can sign updates
that they originate but receive only unsigned updates. This
facilitates less expensive upgrade to BGPsec in resource-limited stub
ASes, and expedites incremental deployment.
6.3.2. Discussion
During partial deployment, there will be BGPsec islands as a result
of this approach to incremental deployment. Updates that originate
within a BGPsec island will generally propagate with signed AS paths
to the edges of that island. As BGPsec adoption grows, the BGPsec
islands will expand outward (subsuming non-BGPsec portions of the
Internet) and/or pairs of islands may join to form larger BGPsec
islands.
6.4. Partial Path Signing
Partial path signing means that a BGPsec AS can be permitted to sign
an update that was received unsigned from a downstream neighbor.
That is, the AS would add its ASN to the AS path and sign the
(previously unsigned) update to other neighboring (upstream) BGPsec
ASes. It was decided that this should not be permitted.
6.4.1. Decision
It was decided that partial path signing in BGPsec will not be
allowed. A BGPsec update must be fully signed, i.e., each AS in the
AS-PATH must sign the update. So in a signed update there must be a
signature corresponding each AS in the AS path.
6.4.2. Discussion
Partial path signing (as described above) implies that the AS path is
not rigorously protected. Rigorous AS path protection is a key
requirement of BGPsec [RFC7353]. Partial path signing clearly re-
introduces the following attack vulnerability: If a BGPsec speaker is
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allowed to sign an unsigned update, and if signed (i.e., partially or
fully signed) updates would be preferred to unsigned updates, then a
faulty, misconfigured or subverted BGPsec speaker can manufacture any
unsigned update it wants (with insertion of a valid origin AS) and
add a signature to it to increase the chance that its update will be
preferred.
6.5. Consideration of Stub ASes with Resource Constraints: Encouraging
Early Adoption
6.5.1. Decision
The protocol permits each pair of BGPsec-capable ASes to negotiate
BGPsec use asymmetrically. Thus, a stub AS (or downstream customer
AS) can agree to perform BGPsec only in the transmit direction and
speak traditional BGP in the receive direction. In this arrangement,
the ISP's (upstream) AS will not send signed updates to this stub or
customer AS. Thus, the stub AS can avoid the need to hardware
upgrade its route processor and RIB memory to support BGPsec update
validation.
6.5.2. Discussion
Various other options were also considered for accommodating a
resource-constrained stub AS as discussed below:
1. An arrangement that can be effected outside of BGPsec
specification is as follows. Through a private arrangement
(invisible to other ASes), an ISP's AS (upstream AS) can truncate
the stub AS (or downstream AS) from the path and sign the update
as if the prefix is originating from ISP's AS (even though the
update originated unsigned from the customer AS). This way the
path will appear fully signed to the rest of the network. This
alternative will require the owner of the prefix at the stub AS
to issue a ROA for the upstream AS, so that the upstream AS is
authorized to originate routes for the prefix.
2. Another type of arrangement that can also be effected outside of
the BGPsec specification is as follows. Stub AS does not sign
updates but obtains an RPKI (CA) certificate, issues a router
certificate under that CA certificate. It passes on the private
key for the router certificate to its upstream provider. That
ISP (i.e., the second hop AS) would insert a signature on behalf
the stub AS using the private key obtained from the stub AS.
This arrangement is called proxy signing (see Section 6.6).
3. An extended ROA is created that includes the stub AS as the
originator of the prefix and the upstream provider as the second
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hop AS, and partial signatures would be allowed (i.e., stub AS
need not sign the updates). It is recognized that this approach
is also authoritative and not trust based. It was observed that
the extended ROA is not much different from what is done with ROA
(in its current form) when a PI address is originated from a
provider's AS. This approach was rejected due to possible
complications with creation and use of a new RPKI object, namely,
the extended ROA. Also, the validating BGPsec router has to
perform a level of indirection with approach, i.e., it must
detect if an update is not fully signed and then look for the
extended ROA to validate.
4. Another method based on a different form of indirection would be
as follows: Customer (stub) AS registers something like a Proxy
Signer Authorization, which authorizes the second hop (i.e.,
provider) AS to sign on behalf of the customer AS using the
provider's own key [Dynamics]. This method allows for fully
signed updates (unlike the Extended ROA based approach). But
this approach also requires the creation of a new RPKI object,
namely, the Proxy Signer Authorization. In this approach, the
second hop AS and validating ASes have to perform a level of
indirection. This approach was also rejected.
The various inputs regarding ISP preferences were taken into
consideration, and eventually the decision in favor of asymmetric
BGPsec was reached (Section 6.5.1). A stub AS that does asymmetric
BGPsec has the advantage that it needs to minimally upgrade to BGPsec
so it can sign updates to its upstream while it receives only
unsigned updates. Thus,it can avoid the cost of increased processing
and memory needed to perform update validations and to store signed
updates in the RIBs, respectively.
6.6. Proxy Signing
6.6.1. Decision
An ISP's AS (or upstream AS) can proxy sign BGP announcements for a
customer (downstream) AS provided that the customer AS obtains an
RPKI (CA) certificate, issues a router certificate under that CA
certificate, and it passes on the private key for that certificate to
its upstream provider. That ISP (i.e., the second hop AS) would
insert a signature on behalf the customer AS using the private key
provided by the customer AS. This is a private arrangement between
the two ASes, and is invisible to other ASes. Thus, this arrangement
is not part of the BGPsec protocol specification.
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BGPsec will not make any special provisions for an ISP to use its own
private key to proxy sign updates for a customer's AS. This type of
proxy signing is considered a bad idea.
6.6.2. Discussion
Consider a scenario when a customer's AS (say, AS8) is multi-homed to
two ISPs, i.e., AS8 peers with AS1 and AS2 of ISP-1 and ISP-2,
respectively. In this case AS8 would have an RPKI (CA) certificate;
it issues two separate router certificates (corresponding to AS1 and
AS2) under that CA certificate; and it passes on the respective
private keys for those two certificates to its upstream providers AS1
and AS2. Thus,AS8 has proxy signing service from both its upstream
ASes. In the future, if the customer AS8 disconnects from ISP-2,
then it would revoke the router certificate corresponding to AS2.
6.7. Multiple Peering Sessions Between ASes
6.7.1. Decision
No problems are anticipated when BGPsec capable ASes have multiple
peering sessions between them (between distinct routers).
6.7.2. Discussion
In traditional BGP, multiple peering sessions, between different
pairs of routers (between two neighboring ASes) may be simultaneously
used for load sharing. Similarly, BGPsec capable ASes can also have
multiple peering sessions between them. Because routers in an AS can
have distinct private keys, the same update when propagated over
these multiple peering sessions will result in multiple updates that
may differ in their signatures. The peer (upstream) AS will apply
its normal procedures for selecting a best path from those multiple
updates (and updates from other peers).
This decision regarding load balancing (vs. using one peering as
primary for carrying data and another as backup) is entirely local
and is up to the two neighboring ASes.
7. Interaction of BGPsec with Common BGP Features
7.1. Peer Groups
In the traditional BGP, the idea of peer groups is used in BGP
routers to save on processing when generating and sending updates.
Multiple peers for whom the same policies apply can be organized into
peer groups. A peer group can typically have tens (maybe as high as
300) of ASes in it.
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7.1.1. Decision
It was decided that BGPsec updates are generated to target unique AS
peers, so there is no support for peer groups in BGPsec.
7.1.2. Discussion
BGPsec router processing can make use of peer groups preceding the
signing of updates to peers. Some of the update processing prior to
forwarding to members of a peer group can be done only once per
update as is done in traditional BGP. Prior to forwarding the
update, a BGPsec speaker adds the peer's ASN to the data that needs
to be signed and signs the update for each peer AS in the group
individually.
If updates were to be signed per peer group, that would require
divulging information about the forward AS-set that constitutes a
peer group (since the ASN of each peer would have to be included in
the update). Some ISPs do not like to share this kind of information
globally.
7.2. Communities
The need to provide protection in BGPsec for the community attribute
was discussed.
7.2.1. Decision
Community attribute(s) will not be included in what is signed in
BGPsec.
7.2.2. Discussion
The community attribute - in its current definition - may be
inherently defective, from a security standpoint. A substantial
amount of work is needed on semantics of the community attribute, and
additional work on its security aspects also needs to be done. The
community attribute is not necessarily transitive; it is often used
only between neighbors. In those contexts, transport security
mechanisms suffice to provide integrity and authentication. (There
is no need to sign data when it is passed only between peers.) It
was suggested that one could include only the transitive community
attributes in what is signed and propagated (across the AS path). It
was noted that there is a flag available (i.e., unused) in the
community attribute, and it might be used by BGPsec (in some
fashion). However, little information is available at this point
about the use and function of this flag. It was speculated that
potentially this flag could be used to indicate to BGPsec if the
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community attribute needs protection. For now, community attributes
will not be secured by BGPsec path signatures.
7.3. Consideration of iBGP Speakers and Confederations
7.3.1. Decision
An iBGP speaker that is also an eBGP speaker, and that executes
BGPsec, will necessarily carry BGPsec data and perform eBGPsec
functions. Confederations are eBGP clouds for administrative
purposes and contain multiple Member-ASes. A Member-AS is not
required to sign updates sent to another Member-AS within the same
confederation. However, if BGPsec signing is applied in eBGP within
a confederation, i.e., each Member-AS signs to the next Member-AS in
the path within the confederation, then upon egress from the
confederation, the Member-AS at the boundary must remove any and all
signatures applied within the confederation. The Member-AS at the
boundary of the confederation will sign the update to an external
eBGPsec peer using the public AS number of the confederation and its
private key. The BGPsec specification will not specify how to
perform this process.
Note: In RFC 8205, signing a BGPsec update between Member-ASes within
a confederation is required if the update were to propagate with
signatures within the confederation. A Confed_Segment flag exists in
each Secure_Path segment, and when set, it indicates that the
corresponding signature belongs to a Member-AS. At the confederation
boundary, all signatures with Confed_Segment flags set are removed
from the update. RFC 8205 specifies in detail how all of this done.
Please see Section 3.1 (Figure 5) and Section 4.3 in [RFC8205] for
the details.
7.3.2. Discussion
This topic may need to be revisited to flesh out the details
carefully.
7.4. Consideration of Route Servers in IXPs
7.4.1. Decision
BGPsec (individual draft-00) makes no special provisions to
accommodate route servers in Internet Exchange Points (IXPs) .
Note: The above decision changed subsequently. RFC 8205 allows
accommodation for IXPs, especially for the case of transparent route
servers. The pCount (AS prepend count) field is set to 0 for
transparent route servers (see Section 4.2 of [RFC8205]). The
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operational guidance for preventing misuse of pCount=0 is given in
Section 7.2 of RFC 8205. Also, see Section 8.4 for a discussion of
security considerations concerning pCount=0.
7.4.2. Discussion
There are basically three methods that an IXP may use to propagate
routes: (A) Direct bilateral peering through the IXP, (B) BGP peering
between clients via a peering with a route server at the IXP (without
IXP inserting its ASN in the path), and (C) BGP peering with an IXP
route server, where the IXP inserts its ASN in the path. (Note:
IXP's route server does not change the NEXT_HOP attribute even if it
inserts its ASN in the path.) It is very rare for an IXP to use
Method C because it is less attractive for the clients if their AS
path length increases by one due to the IXP. A measure of the extent
of use of Method A vs. Method B is given in terms of the
corresponding IP traffic load percentages. As an example, at a major
European IXP, these percentages are about 80% and 20% for Methods A
and B, respectively (this data is based on private communication with
IXPs circa 2011). However, as the IXP grows (in terms of number of
clients), it tends to migrate more towards Method B, because of the
difficulties of managing up to n x (n-1)/2 direct inter-connections
between n peers in Method A.
To the extent an IXP is providing direct bilateral peering between
clients (Method A), that model works naturally with BGPsec. Also, if
the route server in the IXP plays the role of a regular BGPsec
speaker (minus the routing part for payload) and inserts its own ASN
in the path (Method C), then that model would also work well in the
BGPsec Internet and this case is trivially supported in BGPsec.
7.5. Proxy Aggregation (a.k.a. AS_SETs)
7.5.1. Decision
Proxy aggregation (i.e., use of AS_SETs in the AS path) will not be
supported in BGPsec. There is no provision in BGPsec to sign an
update when an AS_SET is part of an AS path. If a BGPsec capable
router receives an update that contains an AS_SET and also finds that
the update is signed, then the router will consider the update
malformed (i.e., protocol error).
Note: In Section 5.2 of RFC 8205, it is specified that a receiving
BGPsec router MUST handle any syntactical or protocol errors in the
BGPsec_PATH attribute by using the "treat-as-withdraw" approach as
defined in RFC 7606 [RFC7606].
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7.5.2. Discussion
Proxy aggregation does occur in the Internet today, but is it very
rare. Only a very small fraction (about 0.1%) of observed updates
contain AS_SETs in the AS path [ASset]. Since traditional BGP
currently allows for proxy aggregation with inclusion of AS_SETs in
the AS path, it is necessary that BGPsec specify what action a
receiving router must take in case such an update is received with
attestation. BCP 172 [RFC6472] recommends against the use of AS_SETs
in updates, so it is anticipated that the use of AS_SETs will
diminish over time.
7.6. 4-Byte AS Numbers
Not all (currently deployed) BGP speakers are capable of dealing with
4-byte ASNs [RFC4893]. The standard mechanism used to accommodate
such speakers requires a peer AS to translate each 4-byte ASN in the
AS path to a reserved 2-byte ASN (23456) before forwarding the
update. This mechanism is incompatible with use of BGPsec, since the
ASN translation is equivalent to a route modification attack and will
cause signatures corresponding to the translated 4-byte ASNs to fail
validation.
7.6.1. Decision
BGP speakers that are BGPsec-capable are required to process 4-byte
ASNs.
7.6.2. Discussion
It is reasonable to assume that upgrades for 4-byte ASN support will
be in place prior to deployment of BGPsec.
8. BGPsec Validation
8.1. Sequence of BGPsec Validation Processing in a Receiver
It is natural to ask in what sequence a receiver must perform BGPsec
update validation so that if a failure were to occur (i.e., update
was determined to be invalid) the processor would have spent the
least amount of processing or other resources.
8.1.1. Decision
There was agreement that the following sequence of receiver
operations is quite meaningful, and are included in the individual
draft-00 BGPsec specification [I-D.lepinski-bgpsec-protocol].
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However, the ordering of validation processing steps is not a
normative part of the BGPsec specification.
1. Verify that the signed update is syntactically correct. For
example, check if the number of signatures match with the number
of ASes in the AS path (after duly accounting for AS prepending).
2. Verify that the origin AS is authorized to advertise the prefix
in question. This verification is based on data from ROAs, and
does not require any crypto operations.
3. Verify that the advertisement has not yet expired.
4. Verify that the target ASN in the signature data matches the ASN
of the router that is processing the advertisement. Note that
the target ASN check is also a non-crypto operation and is fast.
5. Validate the signature data starting from the most recent AS to
the origin.
6. Locate the public key for the router from which the advertisement
was received, using the SKI from the signature data.
7. Hash the data covered by the signature algorithm. Invoke the
signature validation algorithm on the following three inputs: the
locally computed hash, the received signature, and the public
key. There will be one output: valid or invalid.
8. Repeat steps 5 and 6 for each preceding signature in the
Signature-List Block, until the signature data for the origin AS
is encountered and processed, or until either of these steps
fails.
Note: Significant refinements to the above list occurred in the
progress towards RFC 8205. The detailed syntactic error checklist is
presented and explained in Section 5.2 of [RFC8205]. Also, a logical
sequence of steps to be followed in the validation of
Signature_Blocks is described in Section 5.2 of [RFC8205].
8.1.2. Discussion
The suggested sequence of receiver operations described above were
discussed and are viewed as appropriate, if the goal is to minimize
computational costs associated with cryptographic operations. One
additional interesting suggestion was that when there are two
Signature-List Blocks in an update, the validating router can first
verify whichever of the two algorithms is cheaper to save on
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processing. If that Signature-List Block verifies, then the router
can skip validating the other Signature-List Block.
8.2. Signing and Forwarding Updates when Signatures Failed Validation
8.2.1. Decision
A BGPsec router should sign and forward a signed update to upstream
peers if it selected the update as the best path, regardless of
whether the update passed or failed validation (at this router).
8.2.2. Discussion
The availability of RPKI data at different routers (in the same or
different ASes) may differ, depending on the sources used to acquire
RPKI data. Hence an update may fail validation in one AS and the
same update may pass validation in another AS. Also, an update may
fail validation at one router in an AS and the same update may pass
validation at another router in the same AS.
A BCP may be published later in which some conditions of update
failure are identified which may be unambiguous cases for rejecting
the update, in which case the router must not select the AS path in
the update. These cases are TBD.
8.3. Enumeration of Error Conditions
Enumeration of error conditions and the recommendations for reactions
to them are still under discussion.
8.3.1. Decision
TBD. Also, please see Section 8.5 for the decision and discussion
specifically related to syntactic errors in signatures.
Note: Section 5.2 of RFC 8205 describes detection of syntactic and
protocol errors in BGPsec updates as well as how the updates with
such errors are to be handled.
8.3.2. Discussion
The list here is a first cut at some possible error conditions and
recommended receiver reactions in response to detection of those
errors. Refinements will follow after further discussions.
E1 Abnormalities that a peer (i.e., preceding AS) should definitely
not have propagated to a receiving eBGPsec router. Examples: (A)
The number of signatures does not match the number of ASes in the
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AS path (after accounting for AS prepending); (B) There is an
AS_SET in the received update and the update has signatures; (C)
Other syntactic errors with signatures.
Reaction: See Section 8.5.
E2 Situations where a receiving eBGPsec router cannot find the cert
for an AS in the AS_PATH.
Reaction: Mark the update as "Invalid". It is acceptable to
consider the update in best path selection. If it is chosen, then
the router should sign and propagate the update.
E3 Situations where a receiving eBGPsec router cannot find a ROA for
the {prefix, origin} pair in the update.
Reaction: Same as in (E2) above.
E4 The receiving eBGPsec router verifies signatures and finds that
the update is Invalid (even though its peer might not have known,
e.g., due to RPKI skew).
Reaction: Same as in (E2) above.
In some networks, best path selection policy may specify choosing
an unsigned update over one with invalid signature(s). Hence, the
signatures must not be stripped even if the update is "Invalid".
No evil bit is set in the update (when it is Invalid) because an
upstream peer may not get that same answer when it tries to
validate.
8.4. Procedure for Processing Unsigned Updates
An update may come in unsigned from an eBGP peer or internally (e.g.,
as an iBGP update). In the latter case, the route is being
originated from within the AS in consideration.
8.4.1. Decision
If an unsigned route is received from an eBGP peer, and if it is
selected, then the route will be forwarded unsigned to other eBGP
peers, even BGPsec-capable peers. If the route originated in this AS
(IGP or iBGP) and is unsigned, then it should be signed and announced
to external BGPsec-capable peers.
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8.4.2. Discussion
There is also a possibility that an update received in IGP (or iBGP)
may have private AS numbers in the AS path. These private AS numbers
would normally appear in the right most portion of the AS path. It
was noted that in this case, the private AS numbers to the right
would be removed (as done in traditional BGP), and then the update
will be signed by the originating AS and announced to BGPsec-capable
eBGP peers.
Note: See Section 7.5 [RFC8205] for operational considerations for
BGPsec in the context of private AS numbers.
8.5. Response to Syntactic Errors in Signatures and Recommendation for
Reaction
Note: The contents in this subsection (i.e., Section 8.5) differ
substantially from the syntactic and protocol error handling
recommendations for BGPsec in RFC 8205. Hence, the reader may skip
reading this subsection and instead read Section 5.2 of [RFC8205].
This section (Section 8.5) is kept here for the sake of archival
value concerning design discussions.
Different types of error conditions were discussed in Section 8.3.
Here the focus is only on syntactic error conditions in signatures.
8.5.1. Decision
If there are syntactic error conditions such as (a) AS_SET and
Signature-List Block (or Signature_Block per RFC 8205) both appear in
an update, or (b) the number of signatures does not match the number
of ASes (after accounting for any AS prepending), or (c) a parsing
issue occurs with the BGPsec_Path_Signatures attribute, then the
update (with the signatures stripped) will still be considered in the
best path selection algorithm (**Note: This is not true in RFC
8205**). If the update is selected as the best path, then the update
will be propagated unsigned. The error condition will be logged
locally.
A BGPsec router will follow whatever the current IETF (IDR WG)
recommendations are for notifying a peer that it is sending malformed
messages.
In the case when there are two Signature-List Blocks in an update,
and one or more syntactic errors are found to occur within one of
them but the other one is free of any syntactic errors, then the
update will still be considered in the best path selection algorithm
after the syntactically bad Signature-List Block has been removed
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(**Note: This is not true in RFC 8205**). If the update is selected
as the best path, then the update will be propagated with only one
(i.e., the error-free) Signature-List Block. The error condition
will be logged locally.
8.5.2. Discussion
As stated above, a BGPsec router will follow whatever the current
IETF (IDR WG) recommendations are for notifying a peer that it is
sending malformed messages. Question: If the error is persistent,
and there is a full BGP table dump occurring, then would there be
500K such errors resulting in 500K notify messages sent to the erring
peer? The answer was that rate limiting would be applied to the
notify messages which should prevent any overload due to these
messages.
8.6. Enumeration of Validation States
Various validation conditions are possible which can be mapped to
validation states for possible input to BGPsec decision process.
These conditions can be related to whether an update is signed,
Expire Time checked, route origin validation checked against a ROA,
signatures verification passed, etc.
8.6.1. Decision
It was decided that BGPsec validation outcomes will be mapped to one
of only two validation states: (1) Valid - passed all validation
checks (i.e., Expire Time check, route origin and Signature-List
Block validation), and (2) Invalid - all other possibilities.
"Invalid" would include situations such as (1) did not perform
validation due to lack of or insufficient RPKI data, (2) signature
Expire Time check failed, (3) route origin validation failed, and (4)
signature checks were performed and one or more of them failed.
Note: Expire Time is obsolete (see the notes in Section 2.2.1 and
Section 2.2.2). RFC 8205 uses the states 'Valid' and 'Not Valid',
but only with respect to AS path validation (i.e., not including the
result of origin validation); see Section 5.1 of [RFC8205]). 'Not
Valid' includes all conditions in which path validation was attempted
but a 'Valid' result could not be reached (note: path validation is
not attempted in case of syntactic or protocol errors in a BGPsec
update; see Section 5.2 of [RFC8205]). Each Relying Party (RP) is
expected to devise its own policy to suitably factor in the results
from origin validation [RFC6811] and path validation [RFC8205] in its
path selection decision.
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8.6.2. Discussion
It may be noted that the result of update validation is just an
additional input for the BGP decision process. The router's local
policy ultimately has control over what action (regarding BGP path
selection) is taken.
Initially, four validation states were considered: (1) Update is not
signed; (2) Update is signed but router does not have corresponding
RPKI data to perform validation check; (3) Invalid (validation check
performed and failed); (4) Valid (validation check performed and
passed). Later, it was decided that BGPsec validation outcomes will
be mapped to one of only two validation states as stated above. It
was observed that an update can be invalid for many different
reasons. To begin to differentiate these numerous reasons and to try
to enumerate different flavors of the Invalid state is not likely to
be constructive in route selection decision, and may even introduce
to new vulnerability in the system. However, some questions remain
such as the following.
Question: Is there a need to define a separate validation state for
the case when update is not signed but {prefix, origin} pair matched
with ROA information? This question was discussed, and a tentative
conclusion was that this is in principle similar to validation based
on partial path signatures and that was ruled out earlier (see
Section 6.4). So there is no need to add another validation state
for this case; treat it as "Unverified" (i.e., "Invalid") considering
that it is unsigned. Questions still remain, e.g., would the relying
party want to give the update in consideration a higher preference
over another unsigned update that failed origin validation or over a
signed update that failed both signature and ROA validation?
8.7. Mechanism for Transporting Validation State through iBGP
8.7.1. Decision
BGPsec validation need be performed only at eBGP edges. The
validation status of a BGP signed/unsigned update may be conveyed via
iBGP from an ingress edge router to an egress edge router. Local
policy in the AS will determine how the validation status is conveyed
internally, using various pre-existing mechanisms, e.g., setting a
BGP community, or modifying a metric value such as Local_Pref or MED.
A signed update that cannot be validated (except those with syntax
errors) should be forwarded with signatures from the ingress to the
egress router, where it is signed when propagated towards other
eBGPsec speakers in neighboring ASes. Based entirely on local policy
settings, an egress router may trust the validation status conveyed
by an ingress router or it may perform its own validation. The
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latter approach may be used at an operator's discretion, under
circumstances when RPKI skew is known to happen at different routers
within an AS.
Note: An extended community for carrying origin validation state in
iBGP has been specified in RFC 8097 [RFC8097]).
8.7.2. Discussion
The attribute used to represent the validation state can be carried
between ASes if desired. ISPs may like to carry it over their eBGP
links between their own ASes (e.g., sibling ASes). A peer (or
customer) may receive it over an eBGP link from a provider, and may
want to use it to shortcut their own validation check. However, the
peer (or customer) should be aware that this validation-state
attribute is just a preview of a neighbor's validation and must
perform their own validation check to be sure of the actual state of
update's validation. Question: Should validation state propagation
be protected by attestation in case it has utility for diagnostics
purposes? It was decided not to protect the validation state
information using signatures.
The following are intended only as suggestions to be considered by AS
operators.
The following Validation states may be needed for propagation via
iBGP between edge routers in an AS:
o Validation states communicated in iBGP for an unsigned update
(route origin validation result): (1) Valid, (2) Invalid, (3) 'Not
Found' (see [RFC6811]), (4) Validation Deferred.
* An update could be unsigned for two reasons but they need not
be distinguished: (a) Because it had no signatures (came in
unsigned from an eBGP peer), or (b) Signatures were present but
stripped.
o Validation states communicated in iBGP for a Signed update: (1)
Valid, (2) Invalid, (3) Validation Deferred.
The reason for conveying the additional "Validation Deferred" state
may be stated as follows. An ingress edge Router A receiving an
update from an eBGPsec peer may not attempt to validate signatures
(e.g., in a processor overload situation), and in that case Router A
should convey "Validation Deferred" state for that signed update (if
selected for best path) in iBGP to other edge routers. Then an
egress edge Router B upon receiving the update from ingress Router A
would be able to perform its own validation (origin validation for
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unsigned update or origin/signature validation for signed update).
As stated before, the egress Router B may always choose to perform
its own validation when it receives an update from iBGP (independent
of the validation status conveyed in iBGP) to account for the
possibility of RPKI data skew at different routers. These various
choices are local and entirely up to operator discretion.
9. Operational Considerations
Note: Significant thought has been devoted to operations and
management considerations post publication of individual draft-00 of
BGPsec specification. For this, the reader is referred to [RFC8207]
and Section 7 of [RFC8205].
9.1. Interworking with BGP Graceful Restart
BGP Graceful Restart (BGP-GR) [RFC4724] is a mechanism currently used
to facilitate non-stop packet forwarding when the control plane is
recovering from a fault (i.e., BGP session is restarted), but the
data plane is functioning. A question was asked regarding if there
are any special concerns about how BGP-GR works while BGPsec is
operational? Also, what happens if the BGP router operation
transitions from traditional BGP operation to BGP-GR to BGPsec, in
that order?
9.1.1. Decision
No decision was made relative to this issue (at the time of
publication of individual draft-00 of BGPsec specification).
Note: See Section 7.7 of [RFC8205] for comments concerning the
operation of Graceful Restart with BGPsec. They are consistent with
the discussion below.
9.1.2. Discussion
BGP-GR can be implemented with BGPsec just as it is currently
implemented with traditional BGP. The Restart State bit, Forwarding
State bit, End-of-RIB marker, Staleness marker (in RIB-in), and
Selection_Deferral_Timer are key parameters associated with BGP-GR
[RFC4724]. These parameters would apply to BGPsec just as they do
with traditional BGP.
Regarding what happens if the BGP router transitions from traditional
BGP to BGP-GR to BGPsec, the answer would simply be as follows. If
there is software upgrade to BGPsec during BGP-GR (assuming upgrade
is being done on a live BGP speaker), then the BGP-GR session should
be terminated before a BGPsec session is initiated. Once the eBGPsec
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peering session is established, then the receiving eBGPsec speaker
will see signed updates from the sending (newly upgraded) eBGPsec
speaker. There is no apparent harm (it may, in fact, be desirable)
if the receiving speaker continues to use previously-learned unsigned
BGP routes from the sending speaker until they are replaced by new
BGPsec routes. However, if the Forwarding State bit is set to zero
by the sending speaker (i.e., the newly upgraded speaker) during
BGPsec session negotiation, then the receiving speaker would mark all
previously-learned unsigned BGP routes from that sending speaker as
"Stale" in its RIB-in. Then, as BGPsec updates are received
(possibly interspersed with unsigned BGP updates), the "Stale" routes
will be replaced or refreshed.
9.2. BCP Recommendations for Minimizing Churn: Certificate Expiry/
Revocation and Signature Expire Time
9.2.1. Decision
This is still work in progress.
9.2.2. Discussion
BCP recommendations for minimizing churn in BGPsec have been
discussed. There are potentially various strategies on how routers
should react to events such as certificate expiry/revocation,
signature Expire Time exhaustion, etc. [Dynamics]. The details will
be documented in the near future after additional work is completed.
9.3. Outsourcing Update Validation
9.3.1. Decision
Update signature validation and signing can be outsourced to an off-
board server or processor.
9.3.2. Discussion
Possibly an off-router box (one or more per AS) can be used that
performs path validation. For example, these capabilities might be
incorporated into a route reflector. At an ingress router, one needs
the RIB-in entries validated; not the RIB-out entries. So the off-
router box is probably unlike the traditional route reflector; it
sits at the network edge and validates all incoming BGPsec updates.
Thus,it appears that each router passes each BGPsec update it
receives to the off-router box and receives a validation result
before it stores the route in the RIB-in. Question: What about
failure modes here? They would be dependent on (1) How much of the
control plane is outsourced; (2) Reliability of the off-router box
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(or, equivalently communication to and from it); and (3) How
centralized vs. distributed is this arrangement? When any kind of
outsourcing is done, the user needs to be watchful and ensure that
the outsourcing does not cross trust/security boundaries.
9.4. New Hardware Capability
9.4.1. Decision
It is assumed that BGPsec routers (PE routers and route reflectors)
will require significantly upgraded hardware - much more memory for
RIBs and hardware crypto assistance. However, stub ASes would not
need to make such upgrades because they can negotiate asymmetric
BGPsec capability with their upstream ASes, i.e., they sign updates
to the upstream AS but receive only unsigned BGP updates (see
Section 6.5).
9.4.2. Discussion
It is accepted that it might take several years to go beyond test
deployment of BGPsec, because of the need for additional route
processor CPU and memory. However, because BGPsec deployment will be
incremental, and because signed updates are not sent outside of a set
of contiguous BGPsec-enabled ASes, it is not clear how much
additional (RIB) memory will be required during initial deployment.
See (see [RIB_size]) for preliminary results on modeling and
estimation of BGPsec RIB size and its projected growth. Hardware
cryptographic support reduces the computation burden on the route
processor, and offers good security for router private keys.
However, given the incremental deployment model, it also is not clear
how substantial a cryptographic processing load will be incurred,
initially.
Note: There are recent detailed studies that considered software
optimizations for BGPsec. In [Mehmet1] and [Mehmet2], computational
optimizations for cryptographic processing (i.e., ECDSA speedup) are
considered for BGPsec implementations on general purpose CPUs. In
[V_Sriram], software optimizations at the level of update processing
and path selection are proposed and quantified for BGPsec
implementations.
9.5. Signed Peering Registrations
9.5.1. Decision
The idea of signed BGP peering registrations (for the purpose of path
validation) was rejected.
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9.5.2. Discussion
The idea of using a secure map of AS relationships to "validate"
updates was discussed and rejected. The reason for not pursuing such
solutions was that they cannot provide strong guarantees about the
validity of updates. Using these techniques, one can say only that
an update is 'plausible', but cannot say it is 'definitely' valid
(based on signed peering relations alone).
10. Security Considerations
This document requires no security considerations. See [RFC8205] for
security considerations for the BGPsec protocol.
11. IANA Considerations
This document includes no request to IANA.
12. Informative References
[ASset] Sriram, K. and D. Montgomery, "Measurement Data on AS_SET
and AGGREGATOR: Implications for {Prefix, Origin}
Validation Algorithms", IETF SIDR WG presentation, IETF
78, July 2010, <http://www.nist.gov/itl/antd/upload/
AS_SET_Aggregator_Stats.pdf>.
[Borchert]
Borchert, O. and M. Baer, "Subject: Modification request:
draft-ietf-sidr-bgpsec-protocol-14", message to the IETF
SIDR WG Mailing List, 10 February 2016,
<https://www.ietf.org/mail-archive/web/sidr/current/
msg07509.html>.
[CiscoIOS]
"Cisco IOS RFD implementation",
<http://www.cisco.com/en/US/docs/ios/12_2/ip/
configuration/guide/1cfbgp.html#wp1002395>.
[CPUworkload]
Sriram, K. and R. Bush, "Estimating CPU Cost of BGPSEC on
a Router", Presented at RIPE-63; also at IETF-83 SIDR WG
Meeting, March 2012,
<http://www.ietf.org/proceedings/83/slides/
slides-83-sidr-7.pdf>.
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[Dynamics]
Sriram, K. and et al., "Potential Impact of BGPSEC
Mechanisms on Global BGP Dynamics", December 2009, <Work
in progress, Presentation slides available on request>.
[Gueron] Gueron, S. and V. Krasnov, "Fast and side channel
protected implementation of the NIST P-256 Elliptic Curve
for x86-64 platforms", OpenSSL patch ID 3149, October
2013, <https://rt.openssl.org/>.
[I-D.draft-clynn-s-bgp]
Lynn, C., Mukkelson, J., and K. Seo, "Secure BGP (S-BGP)",
June 2003, <http://tools.ietf.org/html/
draft-clynn-s-bgp-protocol-01>.
[I-D.ietf-idr-bgp-extended-messages]
Bush, R., Patel, K., and D. Ward, "Extended Message
support for BGP", draft-ietf-idr-bgp-extended-messages-24
(work in progress), November 2017.
[I-D.ietf-sidrops-bgpsec-rollover]
Weis, B., Gagliano, R., and K. Patel, "BGPsec Router
Certificate Rollover", draft-ietf-sidrops-bgpsec-
rollover-04 (work in progress), December 2017.
[I-D.lepinski-bgpsec-protocol]
Lepinski, M., "BGPSEC Protocol Specification", draft-
lepinski-bgpsec-protocol-00 (work in progress), March
2011.
[I-D.sriram-replay-protection-design-discussion]
Sriram, K. and D. Montgomery, "Design Discussion and
Comparison of Protection Mechanisms for Replay Attack and
Withdrawal Suppression in BGPsec", draft-sriram-replay-
protection-design-discussion-09 (work in progress),
October 2017.
[JunOS] "Juniper JunOS RFD implementation",
<http://www.juniper.net/techpubs/en_US/junos10.4/topics/
usage-guidelines/policy-using-routing-policies-to-damp-
bgp-route-flapping.html>.
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[Mandelberg1]
Mandelberg, D., "Subject: wglc for draft-ietf-sidr-bgpsec-
protocol-11 (Specific topic: Include Address Family
Identifier in the data protected under signature -- to
alleviate security concern)", message to the IETF SIDR WG
Mailing List, 10 February 2015, <https://www.ietf.org/
mail-archive/web/sidr/current/msg06930.html>.
[Mandelberg2]
Mandelberg, D., "Subject: draft-ietf-sidr-bgpsec-protocol-
13's security guarantees (Specific topic: Sign all of the
preceding signed data (rather than just the immediate,
previous signature) -- to alleviate security concern)",
message to the IETF SIDR WG Mailing List, 26 August 2015,
<https://www.ietf.org/mail-archive/web/sidr/current/
msg07241.html>.
[Mao02] Mao, Z. and et al., "Route-flap Damping Exacerbates
Internet Routing Convergence", August 2002,
<http://www.eecs.umich.edu/~zmao/Papers/sig02.pdf>.
[Mehmet1] Adalier, M., "Efficient and Secure Elliptic Curve
Cryptography Implementation of Curve P-256", NIST Workshop
on ECC Standards , June 2015,
<http://csrc.nist.gov/groups/ST/ecc-workshop-2015/papers/
session6-adalier-Mehmet.pdf>.
[Mehmet2] Adalier, M., Sriram, K., Borchert, O., Lee, K., and D.
Montgomery, "High Performance BGP Security: Algorithms and
Architectures", North American Network Operator Group
Meeting NANOG-69, February 2017,
<https://www.nanog.org/meetings/abstract?id=3043>.
[MsgSize] Sriram, K., "Decoupling BGPsec Documents and Extended
Messages draft", Presented in the IETF SIDROPS WG
Meeting, IETF-98, March 2017,
<https://www.ietf.org/proceedings/98/slides/slides-98-
sidrops-decoupling-bgpsec-documents-and-extended-messages-
draft-00.pdf>.
[RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November
1998, <https://www.rfc-editor.org/info/rfc2439>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.
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[RFC4055] Schaad, J., Kaliski, B., and R. Housley, "Additional
Algorithms and Identifiers for RSA Cryptography for use in
the Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile", RFC 4055,
DOI 10.17487/RFC4055, June 2005,
<https://www.rfc-editor.org/info/rfc4055>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
[RFC4724] Sangli, S., Chen, E., Fernando, R., Scudder, J., and Y.
Rekhter, "Graceful Restart Mechanism for BGP", RFC 4724,
DOI 10.17487/RFC4724, January 2007,
<https://www.rfc-editor.org/info/rfc4724>.
[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC4893] Vohra, Q. and E. Chen, "BGP Support for Four-octet AS
Number Space", RFC 4893, DOI 10.17487/RFC4893, May 2007,
<https://www.rfc-editor.org/info/rfc4893>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[RFC5396] Huston, G. and G. Michaelson, "Textual Representation of
Autonomous System (AS) Numbers", RFC 5396,
DOI 10.17487/RFC5396, December 2008,
<https://www.rfc-editor.org/info/rfc5396>.
[RFC5652] Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
RFC 5652, DOI 10.17487/RFC5652, September 2009,
<https://www.rfc-editor.org/info/rfc5652>.
[RFC6090] McGrew, D., Igoe, K., and M. Salter, "Fundamental Elliptic
Curve Cryptography Algorithms", RFC 6090,
DOI 10.17487/RFC6090, February 2011,
<https://www.rfc-editor.org/info/rfc6090>.
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[RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using
AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
DOI 10.17487/RFC6472, December 2011,
<https://www.rfc-editor.org/info/rfc6472>.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/info/rfc6480>.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482,
DOI 10.17487/RFC6482, February 2012,
<https://www.rfc-editor.org/info/rfc6482>.
[RFC6483] Huston, G. and G. Michaelson, "Validation of Route
Origination Using the Resource Certificate Public Key
Infrastructure (PKI) and Route Origin Authorizations
(ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012,
<https://www.rfc-editor.org/info/rfc6483>.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487,
DOI 10.17487/RFC6487, February 2012,
<https://www.rfc-editor.org/info/rfc6487>.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.
[RFC6891] Damas, J., Graff, M., and P. Vixie, "Extension Mechanisms
for DNS (EDNS(0))", STD 75, RFC 6891,
DOI 10.17487/RFC6891, April 2013,
<https://www.rfc-editor.org/info/rfc6891>.
[RFC7132] Kent, S. and A. Chi, "Threat Model for BGP Path Security",
RFC 7132, DOI 10.17487/RFC7132, February 2014,
<https://www.rfc-editor.org/info/rfc7132>.
[RFC7353] Bellovin, S., Bush, R., and D. Ward, "Security
Requirements for BGP Path Validation", RFC 7353,
DOI 10.17487/RFC7353, August 2014,
<https://www.rfc-editor.org/info/rfc7353>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
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[RFC8097] Mohapatra, P., Patel, K., Scudder, J., Ward, D., and R.
Bush, "BGP Prefix Origin Validation State Extended
Community", RFC 8097, DOI 10.17487/RFC8097, March 2017,
<https://www.rfc-editor.org/info/rfc8097>.
[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.
[RFC8207] Bush, R., "BGPsec Operational Considerations", BCP 211,
RFC 8207, DOI 10.17487/RFC8207, September 2017,
<https://www.rfc-editor.org/info/rfc8207>.
[RFC8208] Turner, S. and O. Borchert, "BGPsec Algorithms, Key
Formats, and Signature Formats", RFC 8208,
DOI 10.17487/RFC8208, September 2017,
<https://www.rfc-editor.org/info/rfc8208>.
[RIB_size]
Sriram, K. and et al., "RIB Size Estimation for BGPSEC",
June 2011, <http://www.nist.gov/itl/antd/upload/
BGPSEC_RIB_Estimation.pdf>.
[RIPE580] Bush, R. and et al., "RIPE-580: RIPE Routing Working Group
Recommendations on Route-flap Damping", January 2013,
<http://www.ripe.net/ripe/docs/ripe-580>.
[V_Sriram]
Sriram, V. and D. Montgomery, "Design and analysis of
optimization algorithms to minimize cryptographic
processing in BGP security protocols", Computer
Communications, Vol. 106, pp. 75-85, July 2017,
<http://www.sciencedirect.com/science/article/pii/
S0140366417303365>.
Acknowledgements
The authors would like to thank Jeff Haas and Wes George for serving
as reviewers for this document for the Independent Submissions
stream. The authors are grateful to Nevil Brownlee for shepherding
this document through the Independent Submissions review process.
Many thanks are also due to Michael Baer, Oliver Borchert, David
Mandelberg, Sean Turner, Alvaro Retana, Matthias Waehlisch, Tim Polk,
Russ Mundy, Wes Hardaker, Sharon Goldberg, Ed Kern, Chris Hall, Shane
Amante, Luke Berndt, Doug Maughan, Pradosh Mohapatra, Mark Reynolds,
Heather Schiller, Jason Schiller, Ruediger Volk, and David Ward for
their review, comments, and suggestions during the course of this
work.
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Contributors
The following people have made significant contributions to this
document and should be considered co-authors:
Rob Austein
Dragon Research Labs
Email: sra@hactrn.net
Steven Bellovin
Columbia University
Email: smb@cs.columbia.edu
Randy Bush
Internet Initiative Japan, Inc.
Email: randy@psg.com
Russ Housley
Vigil Security, LLC
Email: housley@vigilsec.com
Stephen Kent
BBN Technologies
Email: kent@alum.mit.edu
Warren Kumari
Google
Email: warren@kumari.net
Matt Lepinski
New College of Florida
mlepinski@ncf.edu
Doug Montgomery
USA National Institute of Standards and Technology
Email: dougm@nist.gov
Chris Morrow
Google, Inc.
Email: morrowc@google.com
Sandy Murphy
SPARTA, Inc., a Parsons Company
Email: sandy@tislabs.com
Keyur Patel
Arrcus
Email: keyur@arrcus.com
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John Scudder
Juniper Networks
Email: jgs@juniper.net
Samuel Weiler
W3C/MIT
Email: weiler@csail.mit.edu
Author's Address
Kotikalapudi Sriram (editor)
USA NIST
100 Bureau Drive
Gaithersburg, MD 20899
USA
Email: ksriram@nist.gov
Sriram Expires July 23, 2018 [Page 48]
