Internet DRAFT - draft-sriram-opsec-urpf-improvements
draft-sriram-opsec-urpf-improvements
OPSEC Working Group K. Sriram
Internet-Draft D. Montgomery
Intended status: Best Current Practice USA NIST
Expires: September 6, 2018 J. Haas
Juniper Networks, Inc.
March 5, 2018
Enhanced Feasible-Path Unicast Reverse Path Filtering
draft-sriram-opsec-urpf-improvements-03
Abstract
This document identifies a need for improvement of the unicast
Reverse Path Filtering techniques (uRPF) [BCP84] for source address
validation (SAV) [BCP38]. The strict uRPF is inflexible about
directionality, the loose uRPF is oblivious to directionality, and
the current feasible-path uRPF attempts to strike a balance between
the two [BCP84]. However, as shown in this draft, the existing
feasible-path uRPF still has short comings. This document describes
an enhanced feasible-path uRPF technique, which aims to be more
flexible (in a meaningful way) about directionality than the
feasible-path uRPF. It can potentially alleviate ISPs' concerns
about the possibility of disrupting service for their customers, and
encourage greater deployment of uRPF techniques.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on September 6, 2018.
Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Review of Existing Source Address Validation Techniques . . . 3
2.1. SAV using Access Control List . . . . . . . . . . . . . . 4
2.2. SAV using Strict Unicast Reverse Path Filtering . . . . . 4
2.3. SAV using Feasible-Path Unicast Reverse Path Filtering . 5
2.4. SAV using Loose Unicast Reverse Path Filtering . . . . . 6
3. SAV using Enhanced Feasible-Path uRPF . . . . . . . . . . . . 7
3.1. Description of the Method . . . . . . . . . . . . . . . . 7
3.1.1. Algorithm A: Enhanced Feasible-Path uRPF . . . . . . 8
3.2. Operational Recommendations . . . . . . . . . . . . . . . 9
3.3. A Challenging Scenario . . . . . . . . . . . . . . . . . 9
3.4. Algorithm B: Enhanced Feasible-Path uRPF with Additional
Flexibility Across Customer Cone . . . . . . . . . . . . 10
3.5. Implementation Considerations . . . . . . . . . . . . . . 11
3.5.1. Impact on FIB Memory Size Requirement . . . . . . . . 11
3.6. Summary of Recommendations . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 13
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
7. Informative References . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
This internet draft identifies a need for improvement of the unicast
Reverse Path Filtering (uRPF) techniques [RFC2827] for source address
validation (SAV) [RFC3704]. The strict uRPF is inflexible about
directionality, the loose uRPF is oblivious to directionality, and
the current feasible-path uRPF attempts to strike a balance between
the two [RFC3704]. However, as shown in this draft, the existing
feasible-path uRPF still has short comings. Even with the feasible-
path uRPF, ISPs are often apprehensive that they may be dropping
customers' data packets with legitimate source addresses.
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This document describes an enhanced feasible-path uRPF technique,
which aims to be more flexible (in a meaningful way) about
directionality than the feasible-path uRPF. It is based on the
principle that if BGP updates for multiple prefixes with the same
origin AS were received on different interfaces (at border routers),
then incoming data packets with source addresses in any of those
prefixes should be accepted on any of those interfaces (presented in
Section 3). For some challenging ISP-customer scenarios (see
Section 3.3), this document also describes a more relaxed version of
the enhanced feasible-path uRPF technique (presented in Section 3.4).
Implementation considerations are discussed in Section 3.5.
Note: Definition of Reverse Path Filtering (RPF) list: The list of
permissible source address prefixes for incoming data packets on a
given interface.
Note: Throughout this document, the routes in consideration are
assumed to have been vetted based on prefix filtering [RFC7454] and
possibly (in the future) origin validation [RFC6811].
The enhanced feasible-path uRPF methods described here are expected
to add greater operational robustness and efficacy to uRPF, while
minimizing ISPs' concerns about accidental service disruption for
their customers. It is expected that this will encourage more
deployment of uRPF to help realize its DDoS prevention benefits
network wide.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Review of Existing Source Address Validation Techniques
There are various existing techniques for mitigation against DDoS
attacks with spoofed addresses [RFC2827] [RFC3704]. There are also
some techniques used for mitigating reflection attacks [RRL]
[TA14-017A], which are used to amplify the impact in DDoS attacks.
Employing a combination of these preventive techniques (as
applicable) in enterprise and ISP border routers, broadband and
wireless access network, data centers, and DNS servers provides
reasonably effective protection against DDoS attacks.
Source address validation (SAV) is performed in network edge devices
such as border routers, Cable Modem Termination Systems (CMTS),
Digital Subscriber Line Access Multiplexers (DSLAM), and Packet Data
Network (PDN) gateways in mobile networks. Ingress Access Control
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List (ACL) and unicast Reverse Path Filtering (uRPF) are techniques
employed for implementing SAV [RFC2827] [RFC3704] [ISOC].
2.1. SAV using Access Control List
Ingress/egress Access Control Lists (ACLs) are maintained which list
acceptable (or alternatively, unacceptable) prefixes for the source
addresses in the incoming Internet Protocol (IP) packets. Any packet
with a source address that does not match the filter is dropped. The
ACLs for the ingress/egress filters need to be maintained to keep
them up to date. Updating the ACLs is an operator driven manual
process, and hence operationally difficult or infeasible.
Typically, the egress ACLs in access aggregation devices (e.g. CMTS,
DSLAM) permit source addresses only from the address spaces
(prefixes) that are associated with the interface on which the
customer network is connected. Ingress ACLs are typically deployed
on border routers, and drop ingress packets when the source address
is spoofed (i.e. belongs to obviously disallowed prefix blocks, RFC
1918 prefixes, or provider's own prefixes).
2.2. SAV using Strict Unicast Reverse Path Filtering
In the strict unicast Reverse Path Filtering (uRPF) method, an
ingress packet at border router is accepted only if the Forwarding
Information Base (FIB) contains a prefix that encompasses the source
address, and forwarding information for that prefix points back to
the interface over which the packet was received. In other words,
the reverse path for routing to the source address (if it were used
as a destination address) should use the same interface over which
the packet was received. It is well known that this method has
limitations when networks are multi-homed and there is asymmetric
routing of packets. Asymmetric routing occurs (see Figure 1) when a
customer AS announces one prefix (P1) to one transit provider (ISP-a)
and a different prefix (P2) to another transit provider (ISP-b), but
routes data packets with source addresses in the second prefix (P2)
to the first transit provider (ISP-a) or vice versa.
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+------------+ ---- P1[AS2 AS1] ---> +------------+
| AS2(ISP-a) | <----P2[AS3 AS1] ---- | AS3(ISP-b)|
+------------+ +------------+
/\ /\
\ /
\ /
\ /
P1[AS1]\ /P2[AS1]
\ /
+-----------------------+
| AS1(customer) |
+-----------------------+
P1, P2 (prefixes originated)
Consider data packets received at AS2
(1) from AS1 with source address in P2, or
(2) from AS3 that originated from AS1
with source address in P1:
* Strict uRPF fails
* Feasible-path uRPF fails
* Loose uRPF works (but ineffective in IPv4)
* Enhanced Feasible-path uRPF works best
Figure 1: Scenario 1 for illustration of efficacy of uRPF schemes.
2.3. SAV using Feasible-Path Unicast Reverse Path Filtering
The feasible-path uRPF helps partially overcome the problem
identified with the strict uRPF in the multi-homing case. The
feasible-path uRPF is similar to the strict uRPF, but in addition to
inserting the best-path prefix, additional prefixes from alternative
announced routes are also included in the RPF table. This method
relies on announcements for the same prefixes (albeit some may be
prepended to effect lower preference) propagating to all routers
performing feasible-path uRPF checks. Therefore, in the multi-homing
scenario, if the customer AS announces routes for both prefixes (P1,
P2) to both transit providers (with suitable prepends if needed for
traffic engineering), then the feasible-path uRPF method works (see
Figure 2). It should be mentioned that the feasible-path uRPF works
in this scenario only if customer routes are preferred at AS2 and AS3
over a shorter non-customer route.
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+------------+ routes for P1, P2 +-----------+
| AS2(ISP-a) |<-------------------->| AS3(ISP-b)|
+------------+ (p2p) +-----------+
/\ /\
\ /
P1[AS1]\ /P2[AS1]
\ /
P2[AS1 AS1 AS1]\ /P1[AS1 AS1 AS1]
\ /
+-----------------------+
| AS1(customer) |
+-----------------------+
P1, P2 (prefixes originated)
Consider data packets received at AS2 via AS3
that originated from AS1 and have source address in P1:
* Feasible-path uRPF works (if customer route to P1
is preferred at AS3 over shorter path)
* Feasible-path uRPF fails (if shorter path to P1
is preferred at AS3 over customer route)
* Loose uRPF works (but ineffective in IPv4)
* Enhanced Feasible-path uRPF works best
Figure 2: Scenario 2 for illustration of efficacy of uRPF schemes.
However, the feasible-path uRPF method has limitations as well. One
form of limitation naturally occurs when the recommendation of
propagating the same prefixes to all routers is not followed.
Another form of limitation can be described as follows. In Scenario
2 (described above, illustrated in Figure 2), it is possible that the
second transit provider (ISP-b or AS3) does not propagate the
prepended route for prefix P1 to the first transit provider (ISP-a or
AS2). This is because AS3's decision policy permits giving priority
to a shorter route to prefix P1 via a peer (AS2) over a longer route
learned directly from the customer (AS1). In such a scenario, AS3
would not send any route announcement for prefix P1 to AS2. Then a
data packet with source address in prefix P1 that originates from AS1
and traverses via AS3 to AS2 will get dropped at AS2.
2.4. SAV using Loose Unicast Reverse Path Filtering
In the loose unicast Reverse Path Filtering (uRPF) method, an ingress
packet at the border router is accepted only if the FIB has one or
more prefixes that encompass the source address. That is, a packet
is dropped if no route exists in the FIB for the source address.
Loose uRPF sacrifices directionality. This method is not effective
for prevention of address spoofing since there is little unrouted
address space in IPv4. It only drops packets if the spoofed address
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is unreachable in the current FIB (e.g. RFC 1918, unallocated,
allocated but currently not routed).
3. SAV using Enhanced Feasible-Path uRPF
3.1. Description of the Method
Enhanced feasible-path uRPF adds greater operational robustness and
efficacy to existing uRPF methods discussed in Section 2. The
technique is based on the principle that if BGP updates for multiple
prefixes with the same origin AS were received on different
interfaces (at border routers), then incoming data packets with
source addresses in any of those prefixes should be accepted on any
of those interfaces. It can be best explained with an example as
follows:
Let us say, a border router of ISP-A has in its Adj-RIB-Ins
[RFC4271]. the set of prefixes {Q1, Q2, Q3} each of which has AS-x
as its origin and AS-x is in ISP-A's customer cone. Further, the
border router received a route for prefix Q1 over a customer facing
interface, while it learned routes for prefixes Q2 and Q3 from a
lateral peer and an upstream transit provider, respectively. In this
example scenario, the enhanced feasible-path uRPF method requires Q1,
Q2, and Q3 be included in the RPF list for the customer interface in
consideration. Loose uRPF (see Section 2.4) is recommended to be
applied to the peer and provider interfaces in consideration.
Thus, enhanced feasible-path uRPF defines feasible paths for customer
interfaces in a more generalized but precise way (as compared to
feasible-path uRPF).
Looking back at Scenarios 1 and 2 (Figure 1 and Figure 2), the
enhanced feasible-path uRPF provides comparable or better performance
than the other uRPF methods. Scenario 3 (Figure 3) further
illustrates the enhanced feasible-path uRPF method with a more
concrete example. In this scenario, the focus is on operation of the
feasible-path uRPF at ISP4 (AS4). ISP4 learns a route for prefix P1
via a customer-to-provider (C2P) interface from customer ISP2 (AS2).
This route for P1 has origin AS1. ISP4 also learns a route for P2
via another C2P interface from customer ISP3 (AS3). Additionally,
AS4 learns a route for P3 via a peer-to-peer (p2p) interface from
ISP5 (AS5). Routes for all three prefixes have the same origin AS
(i.e. AS1). Using the enhanced feasible-path uRPF scheme, given the
commonality of the origin AS across the routes for P1, P2 and P3, AS4
includes all of these prefixes to the RPF list for the customer
interfaces (from AS2 and AS3).
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+----------+ P3[AS5 AS1] +------------+
| AS4(ISP4)|<---------------| AS5(ISP5) |
+----------+ (p2p) +------------+
/\ /\ /\
/ \ /
P1[AS2 AS1]/ \P2[AS3 AS1] /
(C2P)/ \(C2P) /
/ \ /
+----------+ +----------+ /
| AS2(ISP2)| | AS3(ISP3)| /
+----------+ +----------+ /
/\ /\ /
\ / /
P1[AS1]\ /P2[AS1] /P3[AS1]
(C2P)\ /(C2P) /(C2P)
\ / /
+----------------+ /
| AS1(customer) |/
+----------------+
P1, P2, P3 (prefixes originated)
Consider that data packets (sourced from AS1)
may be received at AS4 with source address
in P1, P2 or P3 via any of the neighbors (AS2, AS3, AS5):
* Feasible-path uRPF fails
* Loose uRPF works (but not desirable)
* Enhanced Feasible-path uRPF works best
Figure 3: Scenario 3 for illustration of efficacy of uRPF schemes.
3.1.1. Algorithm A: Enhanced Feasible-Path uRPF
The underlying algorithm in the solution method described above can
be specified as follows (to be implemented in a transit AS):
1. Create the list of unique origin ASes considering only the routes
in the Adj-RIB-Ins of customer interfaces. Call it Set A = {AS1,
AS2, ..., ASn}.
2. Considering all routes in Adj-RIB-Ins for all interfaces
(customer, lateral peer, and provider), form the set of unique
prefixes that have a common origin AS1. Call it Set X1.
3. Include set X1 in Reverse Path Filter (RPF) list on all customer
interfaces on which one or more of the prefixes in set X1 were
received.
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4. Repeat Steps 2 and 3 for each of the remaining ASes in Set A
(i.e., for ASi, where i = 2, ..., n).
3.2. Operational Recommendations
The following operational recommendations will make the operation of
the enhanced feasible-path uRPF robust:
For multi-homed stub AS:
o A multi-homed stub AS SHOULD announce at least one of the prefixes
it originates to each of its transit provider ASes.
For non-stub AS:
o A non-stub AS SHOULD also announce at least one of the prefixes it
originates to each of its transit provider ASes.
o Additionally, from the routes it has learned from customers, a
non-stub AS SHOULD announce at least one route per origin AS to
each of its transit provider ASes.
(Note: It is worth noting that in the above recommendations if "at
least one" is replaced with "all", then even traditional feasible-
path uRPF will work as effectively.)
3.3. A Challenging Scenario
It should be observed that in the absence of ASes adhering the above
recommendations, the following example scenario may be constructed
which poses a challenge for the enhanced feasible-path uRPF (as well
as for traditional feasible-path uRPF). In the scenario illustrated
in Figure 4, since routes for neither P1 nor P2 are propagated on the
AS2-AS4 interface, the enhanced feasible-path uRPF at AS4 will reject
data packets received on that interface with source addresses in P1
or P2.
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+----------+
| AS4(ISP4)|
+----------+
/\ /\
/ \ P1[AS3 AS1]
P1 and P2 not / \ P2[AS3 AS1]
propagated / \ (C2P)
(C2P) / \
+----------+ +----------+
| AS2(ISP2)| | AS3(ISP3)|
+----------+ +----------+
/\ /\
\ / P1[AS1]
P1[AS1] NO_EXPORT \ / P2[AS1]
P2[AS1] NO_EXPORT \ / (C2P)
(C2P) \ /
+----------------+
| AS1(customer) |
+----------------+
P1, P2 (prefixes originated)
Figure 4: Illustration of a challenging scenario.
3.4. Algorithm B: Enhanced Feasible-Path uRPF with Additional
Flexibility Across Customer Cone
Adding further flexibility to the enhanced feasible-path uRPF method
can help address the potential limitation identified above using the
scenario in Figure 4 (Section 3.3). In the following, "route" refers
to a route currently existing in the Adj-RIB-in. Including the
additional degree of flexibility, the modified algorithm (implemented
in a transit AS) can be described as follows (we call this Algorithm
B):
1. Create the set of all directly-connected customer interfaces.
Call it Set I = {I1, I2, ..., Ik}.
2. Create the set of all unique prefixes for which routes exist in
Adj-RIB-Ins for the interfaces in Set I. Call it Set P = {P1,
P2, ..., Pm}.
3. Create the set of all unique origin ASes seen in the routes that
exist in Adj-RIB-Ins for the interfaces in Set I. Call it Set A
= {AS1, AS2, ..., ASn}.
4. Create the set of all unique prefixes for which routes exist in
Adj-RIB-Ins of all lateral peer and provider interfaces such that
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each of the routes has its origin AS belonging in Set A. Call it
Set Q = {Q1, Q2, ..., Qj}.
5. Then, Set Z = Union(P,Q) represents the RPF list for every
customer interface in Set I.
6. Apply loose uRPF method for SAV on all peer and provider
interfaces.
When Algorithm B (which is more flexible than Algorithm A) is
employed, the type of limitation identified in Figure 4 (Section 3.3)
goes away.
3.5. Implementation Considerations
The existing RPF checks in edge routers take advantage of existing
line card implementations to perform the RPF functions. For
implementation of the enhanced feasible-path uRPF, the general
necessary feature would be to extend the line cards to take arbitrary
RPF lists that are not necessarily the same as the existing FIB
contents. In the algorithms (Section 3.1.1 and Section 3.4)
described here, the RPF lists are constructed by applying a set of
rules to all received BGP routes (not just those selected as best
path and installed in FIB).
3.5.1. Impact on FIB Memory Size Requirement
The techniques described here require that there should be FIB memory
(i.e., TCAM) available to store the RPF lists in line cards. For an
ISP's AS, the RPF list size for each line card will roughly and
conservatively equal the total number of prefixes in its customer
cone (assuming the algorithm in Section 3.4 is used). (Note: Most
ISP customer cone scenarios would not require the algorithm in
Section 3.4, but instead be served best by the algorithm in
Section 3.1.1, which requires much less FIB memory.) The following
table shows the measured customer cone sizes for various types of
ISPs [sriram-ripe63]:
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+---------------------------------+---------------------------------+
| Type of ISP | Measured Customer Cone Size in |
| | # Prefixes (in turn this is an |
| | estimate for RPF list size on |
| | line card) |
+---------------------------------+---------------------------------+
| Very Large Global ISP | 32392 |
| ------------------------------- | ------------------------------- |
| Very Large Global ISP | 29528 |
| ------------------------------- | ------------------------------- |
| Large Global ISP | 20038 |
| ------------------------------- | ------------------------------- |
| Mid-size Global ISP | 8661 |
| ------------------------------- | ------------------------------- |
| Regional ISP (in Asia) | 1101 |
+---------------------------------+---------------------------------+
Table 1: Customer cone sizes (# prefixes) for various types of ISPs.
For some super large global ISPs that are at the core of the
Internet, the customer cone size (# prefixes) can be as high as a few
hundred thousand [CAIDA]. But uRPF is most effective when deployed
at ASes at the edges of the Internet where the customer cone sizes
are smaller as shown in Table 1.
A very large global ISP's router line card is likely to have a FIB
size large enough to accommodate 2 to 6 million routes [cisco1].
Similarly, the line cards in routers corresponding to a large global
ISP, a mid-size global ISP, and a regional ISP are likely to have FIB
sizes large enough to accommodate about 1 million, 0.5 million, and
100K routes, respectively [cisco2]. Comparing these FIB size numbers
with the corresponding RPF list size numbers in Table 1, it can be
surmised that the conservatively estimated RPF list size is only a
small fraction of the anticipated FIB memory size under relevant ISP
scenarios.
3.6. Summary of Recommendations
Depending on the scenario, an ISP or enterprise AS operator should
follow one of the following recommendations concerning uRPF/SAV:
1. For directly connected networks, i.e., subnets directly connected
to the AS and not multi-homed, the AS in consideration SHOULD
perform ACL-based SAV.
2. For a directly connected single-homed stub AS (customer), the AS
in consideration SHOULD perform SAV based on the strict uRPF
method.
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3. For all other scenarios:
* If the scenario does not involve complexity such as NO_EXPORT
of routes (see Section 3.3, Figure 4), then the enhanced
feasible-path uRPF method in Algorithm A (see Section 3.1.1)
SHOULD be applied.
* Else, if the scenario involves the aforementioned complexity,
then the enhanced feasible-path uRPF method in Algorithm B
(see Section 3.4) SHOULD be applied.
4. Security Considerations
The security considerations in BCP 38 [RFC2827] and BCP 84 [RFC3704]
apply for this document as well. In addition, AS operator should
apply the uRPF method that performs best (i.e., with zero or
insignificant possibility of dropping legitimate data packets) for
the type of peer (customer, provider, etc.) and the nature of
customer cone scenario that apply (see Section 3.1.1 and
Section 3.4).
5. IANA Considerations
This document does not request new capabilities or attributes. It
does not create any new IANA registries.
6. Acknowledgements
The authors would like to thank Job Snijders, Marco Marzetti, Marco
d'Itri, Nick Hilliard, Gert Doering, Igor Gashinsky, Barry Greene,
and Joel Jaeggli for comments and suggestions.
7. Informative References
[CAIDA] "Information for AS 174 (COGENT-174)", CAIDA Spoofer
Project , <https://spoofer.caida.org/as.php?asn=174>.
[cisco1] "Internet Routing Table Growth Causes ROUTING-FIB-
4-RSRC_LOW Message on Trident-Based Line Cards", Cisco
Trouble-shooting Tech-notes , January 2014,
<https://www.cisco.com/c/en/us/support/docs/routers/asr-
9000-series-aggregation-services-routers/116999-problem-
line-card-00.html>.
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[cisco2] "Cisco Nexus 7000 Series NX-OS Unicast Routing
Configuration Guide, Release 5.x (Chapter: Managing the
Unicast RIB and FIB)", Cisco Configuration Guides , June
2018, <https://www.cisco.com/c/en/us/td/docs/switches/data
center/sw/5_x/nx-
os/unicast/configuration/guide/l3_cli_nxos/
l3_manage-routes.html#22859>.
[ISOC] Vixie (Ed.), P., "Addressing the challenge of IP
spoofing", ISOC report , September 2015,
<https://www.us-cert.gov/ncas/alerts/TA14-017A>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <https://www.rfc-editor.org/info/rfc3704>.
[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>.
[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>.
[RFC7454] Durand, J., Pepelnjak, I., and G. Doering, "BGP Operations
and Security", BCP 194, RFC 7454, DOI 10.17487/RFC7454,
February 2015, <https://www.rfc-editor.org/info/rfc7454>.
[RRL] "Response Rate Limiting in the Domain Name System",
Redbarn blog , <http://www.redbarn.org/dns/ratelimits>.
Sriram, et al. Expires September 6, 2018 [Page 14]
Internet-Draft Enhanced FP-uRPF March 2018
[sriram-ripe63]
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>.
[TA14-017A]
"UDP-Based Amplification Attacks", US-CERT alert
TA14-017A , January 2014,
<https://www.us-cert.gov/ncas/alerts/TA14-017A>.
Authors' Addresses
Kotikalapudi Sriram
USA National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg MD 20899
USA
Email: ksriram@nist.gov
Doug Montgomery
USA National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg MD 20899
USA
Email: dougm@nist.gov
Jeffrey Haas
Juniper Networks, Inc.
1133 Innovation Way
Sunnyvale CA 94089
USA
Email: jhaas@juniper.net
Sriram, et al. Expires September 6, 2018 [Page 15]
