draft-ietf-lsr-isis-area-proxy-04.txt   draft-ietf-lsr-isis-area-proxy-05.txt 
Internet Engineering Task Force T. Li Internet Engineering Task Force T. Li
Internet-Draft S. Chen Internet-Draft S. Chen
Intended status: Experimental V. Ilangovan Intended status: Experimental V. Ilangovan
Expires: March 6, 2021 Arista Networks Expires: May 22, 2021 Arista Networks
G. Mishra G. Mishra
Verizon Inc. Verizon Inc.
September 2, 2020 November 18, 2020
Area Proxy for IS-IS Area Proxy for IS-IS
draft-ietf-lsr-isis-area-proxy-04 draft-ietf-lsr-isis-area-proxy-05
Abstract Abstract
Link state routing protocols have hierarchical abstraction already Link state routing protocols have hierarchical abstraction already
built into them. However, when lower levels are used for transit, built into them. However, when lower levels are used for transit,
they must expose their internal topologies to each other, leading to they must expose their internal topologies to each other, leading to
scale issues. scale issues.
To avoid this, this document discusses extensions to the IS-IS To avoid this, this document discusses extensions to the IS-IS
routing protocol that would allow level 1 areas to provide transit, routing protocol that would allow level 1 areas to provide transit,
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 6, 2021. This Internet-Draft will expire on May 22, 2021.
Copyright Notice Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
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There are four classes of routers that we need to be concerned with There are four classes of routers that we need to be concerned with
in this discussion: in this discussion:
Inside Router A router within the Inside Area that runs Level 1 and Inside Router A router within the Inside Area that runs Level 1 and
Level 2 IS-IS. A router is recognized as an Inside Router by the Level 2 IS-IS. A router is recognized as an Inside Router by the
existence of its LSP in the Level 1 LSDB. existence of its LSP in the Level 1 LSDB.
Area Leader The Area Leader is an Inside Router that is elected to Area Leader The Area Leader is an Inside Router that is elected to
represent the Level 1 area by injecting the Proxy LSP into the represent the Level 1 area by injecting the Proxy LSP into the
Level 2 LSDB. There may be multiple candidates for Area Leader, Level 2 LSDB. There may be multiple candidates for Area Leader,
but only one is elected at a given time. Any Inisde Router can be but only one is elected at a given time. Any Inside Router can be
Area Leader. Area Leader.
Inside Edge Router An Inside Edge Router is an Inside Area Router Inside Edge Router An Inside Edge Router is an Inside Area Router
that has at least one Level 2 interface outside of the Inside that has at least one Level 2 interface outside of the Inside
Area. An interface on an Inside Edge Router that is connected to Area. An interface on an Inside Edge Router that is connected to
an Outside Edge Router is an Area Proxy Boundary. an Outside Edge Router is an Area Proxy Boundary.
Outside Edge Router An Outside Edge Router is a Level 2 router that Outside Edge Router An Outside Edge Router is a Level 2 router that
is outside of the Inside Area that has an adjacency with an Inside is outside of the Inside Area that has an adjacency with an Inside
Edge Router. Edge Router.
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+--------+ || | Outside | +--------+ || | Outside |
|| | Edge | || | Edge |
|| | Router | || | Router |
|| +---------+ || +---------+
Outside Area Outside Area
An example of router classes An example of router classes
All Inside Edge Routers learn the Area Proxy System Identifier from All Inside Edge Routers learn the Area Proxy System Identifier from
the Level 1 LSDB and use that as the system identifier in their Level the Area Proxy TLV advertised by the Area Leader and use that as the
2 IS-IS Hello PDUs (IIHs) on all Outside interfaces. Outside Edge system identifier in their Level 2 IS-IS Hello PDUs (IIHs) on all
Routers should then advertise an adjacency to the Area Proxy System Outside interfaces. Outside Edge Routers should then advertise an
Identifier. This allows all Outside Routers to use the Proxy LSP in adjacency to the Area Proxy System Identifier. This allows all
their SPF computations without seeing the full topology of the Inside Outside Routers to use the Proxy LSP in their SPF computations
Area. without seeing the full topology of the Inside Area.
Area Proxy functionality assumes that all circuits on Inside Routers Area Proxy functionality assumes that all circuits on Inside Routers
are either Level 1-2 circuits within the Inside Area, or Level 2 are either Level 1-2 circuits within the Inside Area, or Level 2
circuits between Outside Edge Routers and Inside Edge Routers. circuits between Outside Edge Routers and Inside Edge Routers.
Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN
mode) with multiple Inside Edge Routers on them are not supported. mode) with multiple Inside Edge Routers on them are not supported.
The Inside Edge Router on any boundary LAN MUST NOT flood Inside The Inside Edge Router on any boundary LAN MUST NOT flood Inside
Router LSPs on this link. Boundary LANs SHOULD NOT be enabled for Router LSPs on this link. Boundary LANs SHOULD NOT be enabled for
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Area Proxy TLV (Section 4.3.2). The Inside Edge Nodes MUST establish Area Proxy TLV (Section 4.3.2). The Inside Edge Nodes MUST establish
forwarding based on this SID. The Area Leader SHALL also include the forwarding based on this SID. The Area Leader SHALL also include the
Area SID in the Proxy LSP so that the remainder of L2 can use it for Area SID in the Proxy LSP so that the remainder of L2 can use it for
path construction. (Section 4.4.13). path construction. (Section 4.4.13).
3. Inside Router Functions 3. Inside Router Functions
All Inside Routers run Level 1-2 IS-IS and must be explicitly All Inside Routers run Level 1-2 IS-IS and must be explicitly
instructed to enable the Area Proxy functionality. To signal their instructed to enable the Area Proxy functionality. To signal their
readiness to participate in Area Proxy functionality, they will readiness to participate in Area Proxy functionality, they will
advertise the Area Proxy TLV. advertise the Area Proxy TLV in their L2 LSP.
3.1. The Area Proxy TLV 3.1. The Area Proxy TLV
The Area Proxy TLV serves multiple functions: The Area Proxy TLV serves multiple functions:
The presence of the Area Proxy TLV in a node's LSP indicates that The presence of the Area Proxy TLV in a node's LSP indicates that
the node is enabled for Area Proxy. the node is enabled for Area Proxy.
An LSP containing the Area Proxy TLV is also an Inside Node. All An LSP containing the Area Proxy TLV is also an Inside Node. All
Inside Nodes, including pseudonodes, MUST advertise the Area Proxy Inside Nodes, including pseudonodes, MUST advertise the Area Proxy
TLV. TLV.
It is a container for sub-TLVs with Area Proxy information. It is a container for sub-TLVs with Area Proxy information.
A node advertises the Area Proxy TLV in its L2 LSP. The Area Proxy A node advertises the Area Proxy TLV in fragment 0 of its L2 LSP.
Nodes MUST NOT advertise the Area Proxy TLV in a L1 LSP. Nodes MUST
ignore the Area Proxy TLV if it is found in a L1 LSP. The Area Proxy
TLV is not used in the Proxy LSP. The format of the Area Proxy TLV TLV is not used in the Proxy LSP. The format of the Area Proxy TLV
is: is:
0 1 2 0 1 2
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length | Sub-TLVs ... | TLV Type | TLV Length | Sub-TLVs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: 20 TLV Type: 20
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any intra-area metrics involved. However, if two paths have equal any intra-area metrics involved. However, if two paths have equal
inter-area metrics, then the intra-area metrics would be used to inter-area metrics, then the intra-area metrics would be used to
compare the paths. compare the paths.
Point-to-Point links between two Inside Routers are considered to be Point-to-Point links between two Inside Routers are considered to be
Inside Area links. LAN links which have a pseudonode LSP in the Inside Area links. LAN links which have a pseudonode LSP in the
Level 1 LSDB are considered to be Inside Area links. Level 1 LSDB are considered to be Inside Area links.
3.3. Responsibilities with respect to the Proxy LSP 3.3. Responsibilities with respect to the Proxy LSP
The Area Leader will generate a Proxy LSP that must be flooded across The Area Leader will generate a Proxy LSP that will be flooded across
the Inside Area. Inside Routers MUST ignore the contents of the the Inside Area. Inside Routers MUST ignore the contents of the
Proxy LSP other than for flooding. Proxy LSP other than for flooding. The Proxy LSP uses the Area Proxy
System Identifier as its Source ID.
4. Area Leader Functions 4. Area Leader Functions
The Area Leader has several responsibilities. First, it MUST inject The Area Leader has several responsibilities. First, it MUST inject
the Area Proxy System Identifier into the Level 1 LSDB. Second, the the Area Proxy System Identifier into the Level 2 LSDB. Second, the
Area Leader MUST generate the Proxy LSP for the Inside Area. Area Leader MUST generate the Proxy LSP for the Inside Area.
4.1. Area Leader Election 4.1. Area Leader Election
The Area Leader is selected using the election mechanisms and TLVs The Area Leader is selected using the election mechanisms and TLVs
described in Dynamic Flooding for IS-IS described in Dynamic Flooding for IS-IS
[I-D.ietf-lsr-dynamic-flooding]. [I-D.ietf-lsr-dynamic-flooding].
4.2. Redundancy 4.2. Redundancy
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4.4.13. The Area SID 4.4.13. The Area SID
When SR is enabled, it may be useful to advertise an Area SID which When SR is enabled, it may be useful to advertise an Area SID which
will direct traffic to any of the Inside Edge Routers. The will direct traffic to any of the Inside Edge Routers. The
information for the Area SID is distributed to all Inside Edge information for the Area SID is distributed to all Inside Edge
Routers using the Area SID sub-TLV (Section 4.3.2) by the Area Routers using the Area SID sub-TLV (Section 4.3.2) by the Area
Leader. Leader.
The Area Leader SHOULD advertise the Area SID information in the The Area Leader SHOULD advertise the Area SID information in the
Proxy LSP as a Node SID as defined in [RFC8667] Section 2.1. The Proxy LSP as a Node SID as defined in [RFC8667] Section 2.1. The
advertisement in the Proxy LSP informs the remainder of the network advertisement in the Proxy LSP informs the Outside Area that packets
that packets directed to the SID will be forwarded by one of the directed to the SID will be forwarded to one of the Inside Edge Nodes
Inside Edge Nodes and the Area SID will be consumed. and the Area SID will be consumed.
Other uses of the Area SID and area SID prefix are outside the scope Other uses of the Area SID and area SID prefix are outside the scope
of this document. Documents which define other use cases for the of this document. Documents which define other use cases for the
Area SID MUST specify whether the SID value should be the same or Area SID MUST specify whether the SID value should be the same or
different from that used in support of Area Proxy. different from that used in support of Area Proxy.
5. Inside Edge Router Functions 5. Inside Edge Router Functions
The Inside Edge Router has two additional and important functions. The Inside Edge Router has two additional and important functions.
First, it MUST generate IIHs that appear to have come from the Area First, it MUST generate IIHs that appear to have come from the Area
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[I-D.ietf-lsr-dynamic-flooding] [I-D.ietf-lsr-dynamic-flooding]
Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda, Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra, T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra,
"Dynamic Flooding on Dense Graphs", draft-ietf-lsr- "Dynamic Flooding on Dense Graphs", draft-ietf-lsr-
dynamic-flooding-07 (work in progress), June 2020. dynamic-flooding-07 (work in progress), June 2020.
[I-D.ietf-lsr-isis-srv6-extensions] [I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08 IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11
(work in progress), April 2020. (work in progress), October 2020.
[ISO10589] [ISO10589]
International Organization for Standardization, International Organization for Standardization,
"Intermediate System to Intermediate System Intra-Domain "Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol for use in Conjunction with the Routing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network Protocol for Providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002. Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and [RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195, dual environments", RFC 1195, DOI 10.17487/RFC1195,
 End of changes. 13 change blocks. 
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