Internet Engineering Task Force L. Ginsberg, Ed.
Internet-Draft Cisco Systems
Intended status: Standards Track A. Przygienda
Expires: September 20, 2016 Ericsson
S. Aldrin
Google
J. Zhang
Juniper Networks, Inc.
March 19, 2016
BIER support via ISIS
draft-ietf-bier-isis-extensions-02
Abstract
Specification of an ISIS extension to support BIER domains and sub-
domains.
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] .
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-
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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 September 20, 2016.
Copyright Notice
Copyright (c) 2016 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 . . . . . . . . . . . . . . 4
4.2. Advertising BIER Information . . . . . . . . . . . . . . 5
5. Procedures . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Enabling a BIER Sub-Domain . . . . . . . . . . . . . . . 5
5.2. Multi Topology and Sub-Domain . . . . . . . . . . . . . . 5
5.3. Encapsulation . . . . . . . . . . . . . . . . . . . . . . 6
5.4. Tree Type . . . . . . . . . . . . . . . . . . . . . . . . 6
5.5. Label advertisements for MPLS Encapsulation . . . . . . . 6
5.6. BFR-id Advertisements . . . . . . . . . . . . . . . . . . 6
5.7. Reporting Misconfiguration . . . . . . . . . . . . . . . 6
5.8. Flooding Reduction . . . . . . . . . . . . . . . . . . . 7
6. Packet Formats . . . . . . . . . . . . . . . . . . . . . . . 7
6.1. BIER Info sub-TLV . . . . . . . . . . . . . . . . . . . . 7
6.2. BIER MPLS Encapsulation sub-sub-TLV . . . . . . . . . . . 8
6.3. Optional BIER sub-domain Tree Type sub-sub-TLV . . . . . 9
6.4. Optional BIER sub-domain BSL conversion sub-sub-TLV . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
9. Normative References . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Bit Index Explicit Replication (BIER)
[I-D.draft-ietf-bier-architecture-03] defines an architecture where
all intended multicast receivers are encoded as bitmask in the
Multicast packet header within different encapsulations such as
[I-D.draft-ietf-bier-mpls-encapsulation-03]. 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.
2. Terminology
Some of the terminology specified in
[I-D.draft-ietf-bier-architecture-03] 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.
BIFT: Bit Index Forwarding Table.
BMS: Bit Mask Set. Set containing bit positions of all BFER
participating in a set.
BMP: Bit Mask Position, a given bit in a BMS.
Invalid BMP: Unassigned Bit Mask Position, consisting of all 0s.
IGP signalled BIER domain: A BIER underlay where the BIER
synchronization information is carried in IGP. Observe that a
multi-topology is NOT a separate BIER domain in IGP.
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.
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BFR-id: An optional, unique identifier for a BFR within a BIER sub-
domain.
Invalid BFR-id: Unassigned BFR-id, consisting of all 0s.
3. IANA Considerations
This document adds the following new sub-TLV to the registry of sub-
TLVs for TLVs 235, 237 [RFC5120] and TLVs 135,236
[RFC5305],[RFC5308].
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 [RFC5226]. 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
2 BIER sub-domain Tree Type
3 BIER sub-domain BSL conversion
4. Concepts
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. Each subdomain
is associated with a single ISIS topology [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 a BIER flooding
domain.
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
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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. 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 X and R flags MUST NOT be set. [RFC7794]
o BIER sub-TLVs MUST NOT be included when a prefix reachability
advertisement is leaked between levels.
5. Procedures
5.1. Enabling a BIER Sub-Domain
A given sub-domain with identifier SD with supported bitstring
lengths MLs in a multi-topology MT [RFC5120] is denoted further as
<MT,SD,MLs> and does not have to be advertised by default by BFRs to
preserve the scaling of the protocol (i.e. ISIS carries no TLVs
containing any of the elements related to <MT,SD>). The
advertisement may be triggered e.g. by a first BIER sub-TLV
(Section 6.1) containing <MT,SD> advertised into the area. The
specific trigger itself is outside the scope of this RFC but can be
for example a VPN desiring to initiate a BIER sub-domain as MI-PMSI
[RFC6513] tree or a pre-configured BFER (since BFERs will always
advertise the BIER sub-TLV to make sure they can be reached). It is
outside the scope of this document to describe what trigger for a
router capable of participating in <MT,SD> is used to start the
origination of the necessary information to join into it.
5.2. 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
conflicting <MT, SD> pair MUST be ignored.
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5.3. Encapsulation
All routers in the flooding scope of the BIER TLVs MUST advertise the
same encapsulation for a given <MT,SD>. A router discovering
encapsulation advertised that is different from its own MUST report a
misconfiguration of a specific <MT,SD>. All received BIER
advertisements associated with the conflicting <MT, SD> pair MUST be
ignored.
5.4. Tree Type
All routers in the flooding scope of the BIER TLVs MAY advertise a
supported tree type for a given <MT,SD>. Tree type indicates the
algorithm used when calculating the optimal path. Currently only the
default algorithm "SPF" is defined - which has a tree type of 0. If
no tree type is advertised tree type 0 is assumed. The supported
tree type MUST be consistent for all routers supporting a given
<MT,SD>.
5.5. Label advertisements for MPLS Encapsulation
A router that desires to participate in <MT,SD> MUST advertise for
each bitstring length it supports in <MT,SD> a label range size that
guarantees to cover the maximum BFR-id injected into <MT,SD> (which
implies a certain maximum set id per bitstring length as described in
[I-D.draft-ietf-bier-architecture-03]). Any router that violates
this condition MUST be excluded from BIER BFTs for <MT,SD>.
5.6. BFR-id Advertisements
Each BFER/BFIR MAY advertise with its TLV<MT,SD> the BFR-id that it
has administratively chosen. A valid BFR-id MUST be unique within
the flooding scope of the BIER advertisments. 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>.
5.7. Reporting Misconfiguration
Whenever an advertisement is received which violates any of the
constraints defined in this document the receiving router MUST report
the misconfiguration.
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5.8. Flooding Reduction
BIER domain information SHOULD change infrequently. Frequent changes
will increase the number of Link State PDU (LSP) updates and
negatively impact performance in the network.
6. Packet Formats
All ISIS BIER information is carried within the TLVs 235, 237
[RFC5120] or TLVs 135 [RFC5305], or TLV 236 [RFC5308].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | subdomain-id | BFR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: as indicated in IANA section.
Length: 1 octet.
Reserved: MUST be 0 on transmission, ignored on reception. May be
used in future versions. 8 bits
subdomain-id: Unique value identifying the BIER sub-domain. 1 octet
BFR-id: A 2 octet field encoding the BFR-id, as documented in
[I-D.draft-ietf-bier-architecture-03]. If no BFR-id has been
assigned this field is set to the invalid BFR-id.
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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.
On violation of any of the following conditions, the receiving router
MUST ignore the encapsulating BIER Info sub-TLV.
o Label ranges in multiple sub-sub-TLV MUST NOT overlap.
o Bitstring lengths in multiple sub-sub-TLVs MUST NOT be identical.
o The sub-sub-TLV MUST include the required bitstring lengths
encoded in precisely the same way as in
[I-D.draft-ietf-bier-mpls-encapsulation-03].
o The label range size MUST be greater than 0.
o All labels in the range MUST represent valid label values
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Lbl Range Size|BS Len | Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: value of 1 indicating MPLS encapsulation.
Length: 1 octet.
Local BitString Length (BS Len): Encoded bitstring length as per [I-
D.draft-ietf-bier-mpls-encapsulation-03]. 4 bits.
Label Range Size: Number of labels in the range used on
encapsulation for this BIER sub-domain for this bitstring length,
1 octet.
Label: First label of the range, 20 bits. The labels are as defined
in [I-D.draft-ietf-bier-mpls-encapsulation-03].
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6.3. Optional BIER sub-domain Tree Type sub-sub-TLV
This sub-sub-TLV carries the information associated with the
supported BIER tree type for a <MT,SD> combination. It is carried
within the BIER Info sub-TLV (Section 6.1) that the router
participates in as BFR. This sub-sub-TLV is optional and its absence
has the same semantics as its presence with Tree Type value 0 (SPF).
When Tree Type 0 is used it is recommended that this sub-sub-TLV be
omitted in order to reduce the space consumed in the parent TLV.
This sub-sub-TLV MUST NOT occur more than once in a BIER Info sub-
TLV. If multiple occurences of this sub-sub-TLV are present in a
single BIER Info sub-TLV the encapsulating BIER Info sub-TLV MUST be
ignored.
If the tree type (implied or explicitly advertised) does not match
the locally configured tree type associated with the matching <MT,
SD> pair the encapsulating sub-TLV MUST be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tree Type |
+-+-+-+-+-+-+-+-+
Type: value of 1 indicating BIER Tree Type.
Length: 1 octet.
Tree Type: 1 octet
6.4. Optional BIER sub-domain BSL conversion sub-sub-TLV
This sub-sub-TLV indicates whether the BFR is capable of imposing a
different Bit String Length (BSL) than the one it received in a BIER
encapsulated packet. Such a capability may allow future, advanced
tree types which ensure simple migration procedures from one BSL to
another in a given <MT,SD> or prevent stable blackholes in scenarios
where not all routers support the same set of BSLs in a given
<MT,SD>. It is carried within the BIER Info sub-TLV (Section 6.1).
This sub-sub-TLV is optional and its absence indicates that the
router is NOT capable of imposing different BSLs but will always
forward the packet with the BSL unchanged. This sub-sub-TLV MAY
occur at most once in a given BIER info sub-TLV. If multiple
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occurences of this sub-sub-TLV are received in a given BIER info sub-
TLV the encapsulating sub-TLV MUST be ignored.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7. Security Considerations
Implementations must assure that malformed TLV and Sub-TLV
permutations do not result in errors which cause hard protocol
failures.
8. Acknowledgements
The RFC is aligned with the
[I-D.draft-ietf-bier-ospf-bier-extensions-01] 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.
9. Normative References
[I-D.draft-ietf-bier-architecture-03]
Wijnands et al., IJ., "Stateless Multicast using Bit Index
Explicit Replication Architecture", internet-draft draft-
ietf-bier-architecture-03.txt, Jan 2016.
[I-D.draft-ietf-bier-mpls-encapsulation-03]
Wijnands et al., IJ., "Bit Index Explicit Replication
using MPLS encapsulation", internet-draft draft-ietf-bier-
mpls-encapsulation-03.txt, Feb 2016.
[I-D.draft-ietf-bier-ospf-bier-extensions-01]
Psenak et al., P., "OSPF Extension for Bit Index Explicit
Replication", internet-draft draft-ietf-bier-ospf-bier-
extensions-01.txt, October 2015.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <http://www.rfc-editor.org/info/rfc1195>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[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,
<http://www.rfc-editor.org/info/rfc5120>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <http://www.rfc-editor.org/info/rfc5305>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<http://www.rfc-editor.org/info/rfc5308>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <http://www.rfc-editor.org/info/rfc6513>.
[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, <http://www.rfc-editor.org/info/rfc7794>.
Authors' Addresses
Les Ginsberg (editor)
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
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Tony Przygienda
Ericsson
300 Holger Way
San Jose, CA 95134
USA
Email: antoni.przygienda@ericsson.com
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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