Internet DRAFT - draft-ietf-bier-isis-extensions
draft-ietf-bier-isis-extensions
Internet Engineering Task Force L. Ginsberg, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track A. Przygienda
Expires: October 1, 2018 Juniper Networks
S. Aldrin
Google
J. Zhang
Juniper Networks, Inc.
March 30, 2018
BIER support via ISIS
draft-ietf-bier-isis-extensions-11
Abstract
This document defines ISIS extensions to support multicast forwarding
using the Bit Index Explicit Replication (BIER) architecture.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on October 1, 2018.
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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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4.1. BIER Domains and Sub-Domains . . . . . . . . . . . . . . 5
4.2. Advertising BIER Information . . . . . . . . . . . . . . 5
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Multi Topology and Sub-Domain . . . . . . . . . . . . . . 5
5.2. BFR-id Advertisements . . . . . . . . . . . . . . . . . . 6
5.3. Logging Misconfiguration . . . . . . . . . . . . . . . . 6
5.4. Flooding Reduction . . . . . . . . . . . . . . . . . . . 6
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. BIER Info sub-TLV . . . . . . . . . . . . . . . . . . . . 7
6.2. BIER MPLS Encapsulation sub-sub-TLV . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Bit Index Explicit Replication (BIER) [RFC8279] defines an
architecture where all intended multicast receivers are encoded as
bitmask in the Multicast packet header within different
encapsulations such as [RFC8296]. A router that receives such a
packet will forward the packet based on the Bit Position in the
packet header towards the receiver(s), following a precomputed tree
for each of the bits in the packet. Each receiver is represented by
a unique bit in the bitmask.
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This document presents necessary extensions to the currently deployed
ISIS for IP [RFC1195] protocol to support distribution of information
necessary for operation of BIER domains and sub-domains. This
document defines a new TLV to be advertised by every router
participating in BIER signaling.
This document defines support for MPLS encapsulation as specified in
[RFC8296]. Support for other encapsulation types is outside the
scope of this document. The use of multiple encapsulation types is
outside the scope of this document.
2. Terminology
Some of the terminology specified in [RFC8279] is replicated here and
extended by necessary definitions:
BIER: Bit Index Explicit Replication (The overall architecture of
forwarding multicast using a Bit Position).
BIER-OL: BIER Overlay Signaling. (The method for the BFIR to learn
about BFER's).
BFR: Bit Forwarding Router (A router that participates in Bit Index
Multipoint Forwarding). A BFR is identified by a unique BFR-
prefix in a BIER domain.
BFIR: Bit Forwarding Ingress Router (The ingress border router that
inserts the BM into the packet). Each BFIR must have a valid BFR-
id assigned.
BFER: Bit Forwarding Egress Router. A router that participates in
Bit Index Forwarding as leaf. Each BFER must be a BFR. Each BFER
must have a valid BFR-id assigned.
BFT: Bit Forwarding Tree used to reach all BFERs in a domain.
BIER sub-domain: A further distinction within a BIER domain
identified by its unique sub-domain identifier. A BIER sub-domain
can support multiple BitString Lengths.
BFR-id: An optional, unique identifier for a BFR within a BIER sub-
domain.
Invalid BFR-id: Unassigned BFR-id. The special value 0 is reserved
for this purpose.
BAR BIER Algorithm. Used to calculate underlay next hops.
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IPA IGP Algorithm. May be used to modify, enhance or replace the
calculation of underlay paths as defined by the BAR value
SPF Shortest Path First routing calculation based on IGP link metric
3. IANA Considerations
This document adds the following new sub-TLV to the registry of Sub-
TLVs for TLVs 135, 235, 236, and 237.
Value: 32 (suggested - to be assigned by IANA)
Name: BIER Info
This document also introduces a new registry for sub-sub-TLVs for the
BIER Info sub-TLV added above. The registration policy is Expert
Review as defined in [RFC8126]. This registry is part of the "IS-IS
TLV Codepoints" registry. The name of the registry is "sub-sub-TLVs
for BIER Info sub-TLV". The defined values are:
Type Name
---- ----
1 BIER MPLS Encapsulation
IANA is requested to set up a registry called "BIER Algorithm
Registry" under category "Bit Index Explicit Replication". The
registration policies [RFC8126] for this registry are:
"Standards Action" for values 0-127
"Specification Required" for values 128-240
"Experimental Use" for values 240-254"
The initial values in the BIER Algorithm Registry are:
0: No BIER specific algorithm is used
1-254: Unassigned
255: Reserved
4. Concepts
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4.1. BIER Domains and Sub-Domains
An ISIS signalled BIER domain is aligned with the scope of
distribution of BFR-prefixes that identify the BFRs within ISIS.
ISIS acts in such a case as the supporting BIER underlay.
Within such a domain, the extensions defined in this document
advertise BIER information for one or more BIER sub-domains. Each
sub-domain is uniquely identified by a subdomain-id (SD). Each
subdomain is associated with a single ISIS topology (MT) [RFC5120],
which may be any of the topologies supported by ISIS. Local
configuration controls which <MT,SD> pairs are supported by a router.
The mapping of sub-domains to topologies MUST be consistent within
the IS-IS flooding domain used to advertise BIER information.
Each BIER sub-domain has as its unique attributes the encapsulation
used and the type of tree it is using to forward BIER frames
(currently always SPF). Additionally, per supported bitstring length
in the sub-domain, each router will advertise the necessary label
ranges to support it.
4.2. Advertising BIER Information
BIER information advertisements are associated with a new sub-TLV in
the extended reachability TLVs. BIER information is always
associated with a host prefix which MUST be a node address for the
advertising node. If this is not the case the advertisement MUST be
ignored. Therefore the following restrictions apply:
o Prefix length MUST be 32 for an IPv4 prefix or 128 for an IPv6
prefix
o When the Prefix Attributes Flags sub-TLV is present N flag MUST be
set and R flag MUST NOT be set. [RFC7794]
o BIER sub-TLVs MUST be included when a prefix reachability
advertisement is leaked between levels.
5. Procedures
5.1. Multi Topology and Sub-Domain
A given sub-domain is supported within one and only one topology.
All routers in the flooding scope of the BIER sub-TLVs MUST advertise
the same sub-domain within the same multi-topology. A router
receiving an <MT,SD> advertisement which does not match the locally
configured pair MUST report a misconfiguration of the received
<MT,SD> pair. All received BIER advertisements associated with the
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conflicting <MT,SD> pair MUST be ignored. Note that in the presence
of such a misconfiguration this will lead to partitioning of the sub-
domian.
Example:
The following combination of advertisements are valid: <0,0> <0,1>
<2,2>.
The following combination of advertisements are invalid: <0,0> <0,1>
<2,0>. Advertisements associated with <0,0> and <2,0> must be
ignored.
5.2. BFR-id Advertisements
If a BFER/BFIR is configured with a BFR-id then it advertises this
value in its BIER advertisements. If no BFR-id is configured then
the value "Invalid BFR-id" is advertised. A valid BFR-id MUST be
unique within the flooding scope of the BIER advertisements. All
BFERs/BFIRs MUST detect advertisement of duplicate valid BFR-IDs for
a given <MT, SD>. When such duplication is detected all of the
routers advertising duplicates MUST be treated as if they did not
advertise a valid BFR-id. This implies they cannot act as BFER or
BFIR in that <MT,SD>.
5.3. Logging Misconfiguration
Whenever an advertisement is received which violates any of the
constraints defined in this document the receiving router MUST
support logging this occurrence. Logging SHOULD be dampened to avoid
excessive output.
5.4. Flooding Reduction
It is expected that changes in BIER domain information which is
advertised by IS-IS occur infrequently. If this expectation is not
met for an extended period of time (more than a few seconds of
burstiness) changes will increase the number of Link State PDU (LSP)
updates and negatively impact performance in the network.
Implementations SHOULD protect against this possibility e.g., by
dampening updates if they occur over an extended period of time.
6. Packet Formats
All ISIS BIER information is carried within the TLVs 235, 237
[RFC5120] or TLVs 135 [RFC5305], or TLV 236 [RFC5308].
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6.1. BIER Info sub-TLV
This sub-TLV carries the information for the BIER sub-domains that
the router participates in as BFR. This sub-TLV MAY appear multiple
times in a given prefix-reachability TLV - once for each sub-domain
supported in the associated topology.
The sub-TLV advertises a single <MT,SD> combination followed by
optional sub-sub-TLVs as described in the following sections.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BAR | IPA | subdomain-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| sub-sub-TLVs (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: as indicated in IANA section.
Length: variable
BAR BIER Algorithm. Specifies a BIER specific algorithm used to
calculate underlay paths to reach BFERs. Values are allocated
from the BIER Algorithm Registry. 1 octet
IPA IGP algorithm. Specifies an IGP Algorithm to either modify,
enhance or replace the calculation of underlay paths to reach
BFERs as defined by the BAR value. Values are from the IGP
Algorithm registry. 1 octet
subdomain-id: Unique value identifying the BIER sub-domain. 1 octet
BFR-id: A 2 octet field encoding the BFR-id, as documented in
[RFC8279]. If no BFR-id has been assigned the value of this field
is set to "Invalid BFR-id", which is defined as illegal in
[RFC8279] .
The use of non-zero values in either the BAR field or the IPA field
is outside the scope of this document. If an implementation does not
support the use of non-zero values in these fields, but receives a
BIER Info sub-TLV containing non-zero values in these fields, it
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SHOULD treat the advertising router as incapable of supporting BIER
(one way of handling incapable routers is documented in section 6.9
of [RFC8279] and additional methods may be defined in the future).
6.2. BIER MPLS Encapsulation sub-sub-TLV
This sub-sub-TLV carries the information for the BIER MPLS
encapsulation including the label range for a specific bitstring
length for a certain <MT,SD>. It is advertised within the BIER Info
sub-TLV (Section 6.1) . This sub-sub-TLV MAY appear multiple times
within a single BIER info sub-TLV.
If the same Bitstring length is repeated in multiple sub-sub-TLVs
inside the same BIER Info Sub-TLV, the BIER Info sub-TLV MUST be
ignored.
Label ranges within all BIER MPLS Encapsulation sub-sub-TLVs across
all BIER Info sub-TLVs advertised by the same BFR MUST NOT overlap.
If overlap is detected, the advertising router MUST be treated as if
it did not advertise any BIER sub-TLVs.
Label values MUST NOT match any of the reserved values defined in
[RFC3032]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Max SI |BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: value of 1 indicating MPLS encapsulation.
Length: 4
Max SI Maximum Set Identifier (section 1 of [RFC8279]) used in the
encapsulation for this BIER sub-domain for this bitstring length,
1 octet. Each SI maps to a single label in the label range. The
first label is for SI=0, the second label is for SI=1, etc. If
the label associated with the Maximum Set Identifier exceeds the
20 bit range the sub-sub-TLV MUST be ignored.
Local BitString Length (BS Len): Encoded bitstring length as per
[RFC8296]. 4 bits.
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Label: First label of the range, 20 bits. The labels are as defined
in [RFC8296].
7. Security Considerations
Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
The Security Considerations section of [RFC8279] discusses the
possibility of performing a Denial of Service (DoS) attack by setting
too many bits in the BitString of a BIER-encapsulated packet.
However, this sort of DoS attack cannot be initiated by modifying the
ISIS BIER advertisements specified in this document. A BFIR decides
which systems are to receive a BIER-encapsulated packet. In making
this decision, it is not influenced by the ISIS control messages.
When creating the encapsulation, the BFIR sets one bit in the
encapsulation for each destination system. The information in the
ISIS BIER advertisements is used to construct the forwarding tables
that map each bit in the encapsulation into a set of next hops for
the host that is identified by that bit, but is not used by the BFIR
to decide which bits to set. Hence an attack on the ISIS control
plane cannot be used to cause this sort of DoS attack.
While a BIER-encapsulated packet is traversing the network, a BFR
that receives a BIER-encapsulated packet with n bits set in its
BitString may have to replicate the packet and forward multiple
copies. However, a given bit will only be set in one copy of the
packet. That means that each transmitted replica of a received
packet has fewer bits set (i.e., is targeted to fewer destinations)
than the received packet. This is an essential property of the BIER
forwarding process as defined in [RFC8279]. While a failure of this
process might cause a DoS attack (as discussed in the Security
Considerations of [RFC8279]), such a failure cannot be caused by an
attack on the ISIS control plane.
Further discussion of BIER specific security considerations can be
found in [RFC8279].
8. Acknowledgements
The RFC is aligned with the [I-D.ietf-bier-ospf-bier-extensions]
draft as far as the protocol mechanisms overlap.
Many thanks for comments from (in no particular order) Hannes
Gredler, Ijsbrand Wijnands, Peter Psenak and Chris Bowers.
Special thanks to Eric Rosen.
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9. References
9.1. Normative References
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
[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>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120,
DOI 10.17487/RFC5120, February 2008,
<https://www.rfc-editor.org/info/rfc5120>.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, DOI 10.17487/RFC5304, October
2008, <https://www.rfc-editor.org/info/rfc5304>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, DOI 10.17487/RFC5310, February
2009, <https://www.rfc-editor.org/info/rfc5310>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
9.2. Informative References
[I-D.ietf-bier-ospf-bier-extensions]
Psenak, P., Kumar, N., Wijnands, I., Dolganow, A.,
Przygienda, T., Zhang, Z., and S. Aldrin, "OSPFv2
Extensions for BIER", draft-ietf-bier-ospf-bier-
extensions-16 (work in progress), March 2018.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
Authors' Addresses
Les Ginsberg (editor)
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
Tony Przygienda
Juniper Networks
Email: prz@juniper.net
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Sam Aldrin
Google
1600 Amphitheatre Parkway
Mountain View, CA
USA
Email: aldrin.ietf@gmail.com
Jeffrey (Zhaohui) Zhang
Juniper Networks, Inc.
10 Technology Park Drive
Westford, MA 01886
USA
Email: zzhang@juniper.net
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