Internet Engineering Task Force T. Li
Internet-Draft S. Chen
Intended status: Standards Track V. Ilangovan
Expires: December 25, 2020 Arista Networks
G. Mishra
Verizon Inc.
June 23, 2020
Area Proxy for IS-IS
draft-li-lsr-isis-area-proxy-07
Abstract
Link state routing protocols have hierarchical abstraction already
built into them. However, when lower levels are used for transit,
they must expose their internal topologies to each other, leading to
scale issues.
To avoid this, this document discusses extensions to the IS-IS
routing protocol that would allow level 1 areas to provide transit,
yet only inject an abstraction of the level 1 topology into level 2.
Each level 1 area is represented as a single level 2 node, thereby
enabling greater scale.
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 December 25, 2020.
Copyright Notice
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Area Proxy . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Segment Routing . . . . . . . . . . . . . . . . . . . . . 5
3. Inside Router Functions . . . . . . . . . . . . . . . . . . . 6
3.1. The Area Proxy Router Capability . . . . . . . . . . . . 6
3.2. Level 2 SPF Computation . . . . . . . . . . . . . . . . . 6
3.3. The Inside Node TLV . . . . . . . . . . . . . . . . . . . 7
4. Area Leader Functions . . . . . . . . . . . . . . . . . . . . 7
4.1. Area Leader Election . . . . . . . . . . . . . . . . . . 7
4.2. Redundancy . . . . . . . . . . . . . . . . . . . . . . . 8
4.3. The Area Proxy TLV . . . . . . . . . . . . . . . . . . . 8
4.3.1. The Area Proxy System Id Sub-TLV . . . . . . . . . . 8
4.3.2. The Area Segment SID Sub-TLV . . . . . . . . . . . . 9
4.4. Area Proxy LSP Generation . . . . . . . . . . . . . . . . 10
4.4.1. The Protocols Supported TLV . . . . . . . . . . . . . 10
4.4.2. The Area Address TLV . . . . . . . . . . . . . . . . 10
4.4.3. The Dynamic Hostname TLV . . . . . . . . . . . . . . 10
4.4.4. The IS Neighbors TLV . . . . . . . . . . . . . . . . 10
4.4.5. The Extended IS Neighbors TLV . . . . . . . . . . . . 11
4.4.6. The MT Intermediate Systems TLV . . . . . . . . . . . 11
4.4.7. Reachability TLVs . . . . . . . . . . . . . . . . . . 11
4.4.8. The Router Capability TLV . . . . . . . . . . . . . . 12
4.4.9. The Multi-Topology TLV . . . . . . . . . . . . . . . 12
4.4.10. The SID/Label Binding and The Multi-Topology
SID/Label Binding SID TLV . . . . . . . . . . . . . . 13
4.4.11. The Area Segment SID TLV . . . . . . . . . . . . . . 13
4.4.11.1. Flags . . . . . . . . . . . . . . . . . . . . . 14
4.4.12. The SRv6 Locator TLV . . . . . . . . . . . . . . . . 14
4.4.13. Traffic Engineering Information . . . . . . . . . . . 14
5. Inside Edge Router Functions . . . . . . . . . . . . . . . . 14
5.1. Generating L2 IIHs to Outside Routers . . . . . . . . . . 15
5.2. Filtering LSP information . . . . . . . . . . . . . . . . 15
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
8. Security Considerations . . . . . . . . . . . . . . . . . . . 16
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9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
9.3. URIs . . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
The IS-IS routing protocol IS-IS [ISO10589] currently supports a two-
level hierarchy of abstraction. The fundamental unit of abstraction
is the 'area', which is a (hopefully) connected set of systems
running IS-IS at the same level. Level 1, the lowest level, is
abstracted by routers that participate in both Level 1 and Level 2,
and they inject area information into Level 2. Level 2 systems
seeking to access Level 1, use this abstraction to compute the
shortest path to the Level 1 area. The full topology database of
Level 1 is not injected into Level 2, only a summary of the address
space contained within the area, so the scalability of the Level 2
Link State Database (LSDB) is protected.
This works well if the Level 1 area is tangential to the Level 2
area. This also works well if there are several routers in both
Level 1 and Level 2 and they are adjacent, so Level 2 traffic will
never need to transit Level 1 only routers. Level 1 will not contain
any Level 2 topology, and Level 2 will only contain area abstractions
for Level 1.
Unfortunately, this scheme does not work so well if the Level 1 only
area needs to provide transit for Level 2 traffic. For Level 2
shortest path first (SPF) computations to work correctly, the transit
topology must also appear in the Level 2 LSDB. This implies that all
routers that could provide transit, plus any links that might also
provide Level 2 transit must also become part of the Level 2
topology. If this is a relatively tiny portion of the Level 1 area,
this is not overly painful.
However, with today's data center topologies, this is problematic. A
common application is to use a Layer 3 Leaf-Spine (L3LS) topology,
which is a folded 3-stage Clos [Clos] fabric. It can also be thought
of as a complete bipartite graph. In such a topology, the desire is
to use Level 1 to contain the routing dynamics of the entire L3LS
topology and then to use Level 2 for the remainder of the network.
Leaves in the L3LS topology are appropriate for connection outside of
the data center itself, so they would provide connectivity for Level
2. If there are multiple connections to Level 2 for redundancy, or
other areas, these too would also be made to the leaves in the
topology. This creates a difficulty because there are now multiple
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Level 2 leaves in the topology, with connectivity between the leaves
provided by the spines.
Following the current rules of IS-IS, all spine routers would
necessarily be part of the Level 2 topology, plus all links between a
Level 2 leaf and the spines. In the limit, where all leaves need to
support Level 2, it implies that the entire L3LS topology becomes
part of Level 2. This is seriously problematic as it more than
doubles the LSDB held in the L3LS topology and eliminates any
benefits of the hierarchy.
This document discusses the handling of IP traffic. Supporting MPLS
based traffic is a subject for future work.
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 BCP 14 [1] [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
2. Area Proxy
To address this, we propose to completely abstract away the details
of the Level 1 area topology within Level 2, making the entire area
look like a single proxy system directly connected to all of the
area's Level 2 neighbors. By only providing an abstraction of the
topology, Level 2's requirement for connectivity can be satisfied
without the full overhead of the area's internal topology. It then
becomes the responsibility of the Level 1 area to ensure the
forwarding connectivity that's advertised.
For this discussion, we'll consider a single Level 1 IS-IS area to be
the Inside Area, and the remainder of the Level 2 area is the Outside
Area. All routers within the Inside Area speak Level 1 and Level 2
IS-IS on all of the links within the topology. We propose to
implement Area Proxy by having a Level 2 Proxy Link State Protocol
Data Unit (PDU, LSP) that represents the entire Inside Area. This is
the only LSP from the area that will be flooded into the overall
Level 2 LSDB.
There are four classes of routers that we need to be concerned with
in this discussion:
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
existence of its LSP in the Level 1 LSDB.
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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
Level 2 LSDB. There may be multiple candidates for Area Leader,
but only one is elected at a given time.
Inside Edge Router An Inside Edge Router is an Inside Area Router
that has at least one Level 2 interface outside of the Inside
Area. An interface on an Inside Edge Router that is connected to
an Outside Edge Router is an Area Proxy Boundary.
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
Edge Router.
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
2 IS-IS Hello PDUs (IIHs) on all Outside interfaces. Outside Edge
Routers should then advertise an adjacency to the Area Proxy System
Identifier. This allows all Outside Routers to use the Proxy LSP in
their SPF computations without seeing the full topology of the Inside
Area.
Area Proxy functionality assumes that all circuits on Inside Routers
are either Level 1-2 circuits within the Inside Area, or Level 2
circuits between Outside Edge Routers and Inside Edge Routers.
Area Proxy Boundary multi-access circuits (i.e. Ethernets in LAN
mode) with multiple Inside Edge Routers on them are not supported.
The Inside Edge Router on any boundary LAN MUST NOT flood Inside
Router LSPs on this link. Boundary LANs SHOULD NOT be enabled for
Level 1. An Inside Edge Router may be elected the DIS for a Boundary
LAN. In this case using the Area Proxy System Id as the basis for
the LAN pseudonode identifier could create a collision, so the
Insider Edge Router SHOULD compose the pseudonode identifier using
its native system identifier.
2.1. Segment Routing
If the Inside Area supports Segment Routing [RFC8402], then all
Inside Nodes MUST advertise an SR Global Block (SRGB). The first
value of the SRGB advertised by all Inside Nodes MUST start at the
same value. The range advertised for the area will be the minimum of
all Inside Nodes.
To support Segment Routing, the Area Leader will take the global SID
information found in the L1 LSDB and convey that to L2 through the
Proxy LSP. Prefixes with SID assignments will be copied to the Proxy
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LSP. Adjacency SIDs for Outside Edge Nodes will be copied to the
Proxy LSP.
To further extend Segment Routing, it would be helpful to have a SID
that refers to the entire Inside Area. This allows a path to refer
to an area and have any node within that area accept and forward the
packet. In effect, this becomes an anycast SID that is accepted by
all Inside Edge Nodes. The information about this SID is distributed
in the Area Segment SID Sub-TLV, as part of the Area Leader's 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
Area Segment SID TLV in the Area Proxy LSP so that the remainder of
L2 can use it for path construction (Section 4.4.11). These two TLVs
are similar in structure, so care must be taken not to confuse them.
3. Inside Router Functions
All Inside Routers run Level 1-2 IS-IS and must be explicitly
instructed to enable the Area Proxy functionality. To signal their
readiness to participate in Area Proxy functionality, they will
advertise the Area Proxy Router Capability as part of its Level 1
Router Capability TLV.
3.1. The Area Proxy Router Capability
The Area Proxy Router Capability is a sub-TLV of the Router
Capability TLV [RFC7981] and has the following format:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: LLL
TLV Length: 0
A router advertising this TLV indicates that it is running Level 1-2
and is prepared to perform Area Proxy functions.
3.2. Level 2 SPF Computation
When Outside Routers perform a Level 2 SPF computation, they will use
the Area Proxy LSP for computing a path transiting the Inside Area.
Because the topology has been abstracted away, the cost for
transiting the Inside Area will be zero.
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When Inside Routers perform a Level 2 SPF computation, they MUST
ignore the Area Proxy LSP. Further, because these systems do see the
Inside Area topology, the link metrics internal to the area are
visible. This could lead to different and possibly inconsistent SPF
results, potentially leading to forwarding loops.
To prevent this, the Inside Routers MUST consider the metrics of
links outside of the Inside Area (inter-area metrics) separately from
the metrics of the Inside Area links (intra-area metrics). Intra-
area metrics MUST be treated as less than any inter-area metric.
Thus, if two paths have different total inter-area metrics, the path
with the lower inter-area metric would be preferred, regardless of
any intra-area metrics involved. However, if two paths have equal
inter-area metrics, then the intra-area metrics would be used to
compare the paths.
Point-to-Point links between two Inside Routers are considered to be
Inside Area links. LAN links which have a pseudonode LSP in the
Level 1 LSDB are considered to be Inside Area links.
3.3. The Inside Node TLV
To simplify determining which nodes belong to the Inside Area, all
Inside Nodes MUST insert the Inside Node TLV into their LSP and into
any Inside Area pseudonode LSPs. The format of the Inside Node TLV
is:
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: ZZZ
Length: Zero (0)
4. Area Leader Functions
The Area Leader has several responsibilities. First, it MUST inject
the Area Proxy System Identifier into the Level 1 LSDB. Second, the
Area Leader MUST generate the Proxy LSP for the Inside Area.
4.1. Area Leader Election
The Area Leader is selected using the election mechanisms and TLVs
described in Dynamic Flooding for IS-IS
[I-D.ietf-lsr-dynamic-flooding].
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4.2. Redundancy
If the Area Leader fails, another candidate may become Area Leader
and MUST regenerate the Area Proxy LSP. The failure of the Area
Leader is not visible outside of the area and appears to simply be an
update of the Area Proxy LSP.
For consistency, all Area Leader candidates SHOULD be configured with
the same Proxy System Id, Proxy Hostname, and any other information
that may be inserted into the Proxy LSP.
4.3. The Area Proxy TLV
The Area Proxy TLV is a container for sub-TLVs with Area Proxy
Information. This TLV is injected into the Area Leader's Level 1
LSP.
The format of the Area Proxy TLV is:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Type | TLV Length | Sub-TLVs ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
TLV Type: YYY
TLV Length: length of the sub-TLVs
4.3.1. The Area Proxy System Id Sub-TLV
The Area Proxy System Id Sub-TLV MUST be used by the Area Leader to
distribute the Area Proxy System Id. This is an additional system
identifier that is used by Inside Nodes. The format of this sub-TLV
is:
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 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Proxy System ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Proxy System Identifier continued |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type: AAA
Length: length of a system ID (6)
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Proxy System Identifier: the Area Proxy System Identifier.
The Area Leader SHOULD advertise the Area Proxy System Identifier
Sub-TLV when it observes that all Inside Routers are advertising the
Area Proxy Router Capability. Their advertisements indicate that
they are individually ready to perform Area Proxy functionality. The
Area Leader then advertises the Area Proxy System Identifier TLV to
indicate that the Inside Area SHOULD enable Area Proxy functionality.
Other candidates for Area Leader MAY also advertise the Area Proxy
System Identifier when they observe that all Inside Routers are
advertising the Area Proxy Router Capability. All candidates
advertising the Area Proxy System Identifier TLV MUST be advertising
the same system identifier. Multiple proxy system identifiers in a
single area is a misconfiguration and each unique occurrence SHOULD
be logged.
The Area Leader and other candidates for Area Leader MAY withdraw the
Area Proxy System Identifier when one or more Inside Routers are not
advertising the Area Proxy Router Capability. This will disable Area
Proxy functionality. However, before withdrawing the Area Proxy
System Identifier, an implementation SHOULD protect against
unnecessary churn from transients by delaying the withdrawal. The
amount of delay is implementation-dependent.
4.3.2. The Area Segment SID Sub-TLV
The Area Segment SID Sub-TLV allows the Area Leader to advertise a
SID that represents the entirety of the Inside Area to the Outside
Area. This sub-TLV is learned by all of the Inside Edge Nodes who
should consume this SID at forwarding time. The Area Segment SID
Sub-TLV has the format:
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 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: BBB
Length: variable (1 + SID length)
Flags: 1 octet, see Section 4.4.11.1
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SID/Index/Label: as defined in [RFC8667] Section 2.1.1.1
4.4. Area Proxy LSP Generation
Each Inside Router generates a Level 2 LSP, and the Level 2 LSPs for
the Inside Edge Routers will include adjacencies to Outside Edge
Routers. Unlike normal Level 2 operations, these LSPs are not
advertised outside of the Inside Area and MUST be filtered by all
Inside Edge Routers to not be flooded to Outside Routers. Only the
Area Proxy LSP is injected into the overall Level 2 LSDB.
The Area Leader uses the Level 2 LSPs generated by the Inside Edge
Routers to generate the Area Proxy LSP. This LSP is originated using
the Area Proxy System Identifier. The Area Leader MAY also insert
the following additional TLVs into the Area Proxy LSP for additional
information for the Outside Area. LSPs generated by unreachable
nodes MUST NOT be considered.
4.4.1. The Protocols Supported TLV
The Area Leader SHOULD insert a Protocols Supported TLV (129)
[RFC1195] into the Area Proxy LSP. The values included in the TLV
SHOULD be the protocols supported by the Inside Area.
4.4.2. The Area Address TLV
The Area Leader SHOULD insert an Area Addresses TLV (1) [ISO10589]
into the Area Proxy LSP.
4.4.3. The Dynamic Hostname TLV
It is RECOMMENDED that the Area Leader insert the Dynamic Hostname
TLV (137) [RFC5301] into the Area Proxy LSP. The contents of the
hostname may be specified by configuration. The presence of the
hostname helps to simplify debugging the network.
4.4.4. The IS Neighbors TLV
The Area Leader MAY insert the IS Neighbors TLV (2) [ISO10589] into
the Area Proxy LSP for Outside Edge Routers. The Area Leader learns
of the Outside Edge Routers by examining the LSPs generated by the
Inside Edge Routers copying any IS Neighbors TLVs referring to
Outside Edge Routers into the Proxy LSP. Since the Outside Edge
Routers advertise an adjacency to the Area Proxy System Identifier,
this will result in a bi-directional adjacency.
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An entry for a neighbor in both the IS Neighbors TLV and the Extended
IS Neighbors would be functionally redundant, so the Area Leader
SHOULD NOT do this.
4.4.5. The Extended IS Neighbors TLV
The Area Leader MAY insert the Extended IS Reachability TLV (22)
[RFC5305] into the Area Proxy LSP. The Area Leader SHOULD copy each
Extended IS Reachability TLV advertised by an Inside Edge Router
about an Outside Edge Router into the Proxy LSP.
If the Inside Area supports Segment Routing and Segment Routing
selects a SID where the L-Flag is unset, then the Area Lead SHOULD
include an Adjacency Segment Identifier sub-TLV (31) [RFC8667] using
the selected SID.
If the inside area supports SRv6, the Area Leader SHOULD copy the
"SRv6 End.X SID" and "SRv6 LAN End.X SID" sub-TLVs of the extended IS
reachability TLVs advertised by Inside Edge Routers about Outside
Edge Routers.
If the inside area supports Traffic Engineering (TE), the Area Leader
SHOULD copy TE related sub-TLVs [RFC5305] Section 3 to each Extended
IS Reachability TLV in the Proxy LSP.
4.4.6. The MT Intermediate Systems TLV
If the Inside Area supports Multi-Topology, then the Area Leader
SHOULD copy each Outside Edge Router advertisement that is advertised
by an Inside Edge Router in a MT Intermediate Systems TLV into the
Proxy LSP.
4.4.7. Reachability TLVs
The Area Leader SHOULD insert additional TLVs describing any routing
prefixes that should be advertised on behalf of the area. These
prefixes may be learned from the Level 1 LSDB, Level 2 LSDB, or
redistributed from another routing protocol. This applies to all of
various types of TLVs used for prefix advertisement:
IP Internal Reachability Information TLV (128) [RFC1195]
IP External Reachability Information TLV (130) [RFC1195]
Extended IP Reachability TLV (135) [RFC5305]
IPv6 Reachability TLV (236) [RFC5308]
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Multi-Topology Reachable IPv4 Prefixes TLV (235) [RFC5120]
Multi-Topology Reachable IPv6 Prefixes TLV (237) [RFC5120]
For TLVs in the Level 1 LSDB, for a given TLV type and prefix, the
Area Leader SHOULD select the TLV with the lowest metric and copy
that TLV into the Area Proxy LSP.
When examining the Level 2 LSDB for this function, the Area Leader
SHOULD only consider TLVs advertised by Inside Routers. Further, for
prefixes that represent Boundary links, the Area Leader SHOULD copy
all TLVs that have unique sub-TLV contents.
If the Inside Area supports Segment Routing and the selected TLV
includes a Prefix Segment Identifier sub-TLV (3) [RFC8667], then the
sub-TLV SHOULD be copied as well. The P-Flag SHOULD be set in the
copy of the sub-TLV to indicate that penultimate hop popping SHOULD
NOT be performed for this prefix. The E-Flag SHOULD be reset in the
copy of the sub-TLV to indicate that an explicit NULL is not
required. The R-Flag SHOULD simply be copied.
4.4.8. The Router Capability TLV
The Area Leader MAY insert the Router Capability TLV (242) [RFC7981]
into the Area Proxy LSP. If Segment Routing is supported by the
inside area, as indicated by the presence of an SRGB being advertised
by all Inside Nodes, then the Area Leader SHOULD advertise an SR-
Capabilities sub-TLV (2) [RFC8667] with an SRGB. The first value of
the SRGB is the same value as the first value advertised by all
Inside Nodes. The range advertised for the area will be the minimum
of all ranges advertised by Inside Nodes. The Area Leader SHOULD use
its own Router Id in the Router Capability TLV.
If SRv6 Capability sub-TLV [RFC7981] is advertised by all Inside
Routers, the Area Leader should insert an SRv6 Capability sub-TLV in
the Router Capability TLV. Each flag in the SRv6 Capability sub-TLV
should be set if the flag is set by all Inside Routers.
If the Node Maximum SID Depth (MSD) sub-TLV [RFC8491] is advertised
by all Inside Routers, the Area Leader should advertise common MSD
types and the smallest supported MSD values for each type.
4.4.9. The Multi-Topology TLV
If the Inside Area supports multi-topology, then the Area Leader
SHOULD insert the Multi-Topology TLV (229) [RFC5120], including the
topologies supported by the Inside Nodes.
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If any Inside Node is advertising the 'O' (Overload) bit for a given
topology, then the Area Leader MUST advertise the 'O' bit for that
topology. If any Inside Node is advertising the 'A' (Attach) bit for
a given topology, then the Area Leader MUST advertise the 'A' bit for
that topology.
4.4.10. The SID/Label Binding and The Multi-Topology SID/Label Binding
SID TLV
If an Inside Node advertises the SID/Label Binding or Multi-Topology
SID/Label Binding SID TLV [RFC8667], then the Area Leader MAY copy
the TLV to the Area Proxy LSP.
4.4.11. The Area Segment SID TLV
If the Area Leader is advertising an Area Segment SID in the Area
Segment SID sub-TLV of the Area Proxy TLV, then the Area Leader
SHOULD advertise the Area Segment SID TLV in the Proxy LSP. The
advertisement in the Proxy LSP informs the remainder of the network
that packets directed to the SID will be forwarded by one of the
Inside Edge Nodes and the Area Segment SID will be consumed.
This TLV is not specific to Area Proxy and MAY be used by Edge
Routers in conventional areas. The Area Segment SID TLV has the
format:
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 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SID/Index/Label (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
where:
Type: XXX
Length: variable (1 + SID length)
Flags: 1 octet, see below
SID/Index/Label: as defined in [RFC8667] Section 2.1.1.1
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4.4.11.1. Flags
The Flags octet is defined as follows:
0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+
|F|V|L| |
+-+-+-+-+-+-+-+-+
where:
F: Address-Family Flag. If unset, then this proxy SID is used
when forwarding IPv4-encapsulated traffic. If set, then this
proxy SID is used when forwarding IPv6-encapsulated traffic.
V: Value Flag. If set, then the proxy SID carries a value.
L: Local Flag. If set, then the value/index carried by the proxy
SID has local significance.
Other bits: MUST be zero when originated and ignored when
received.
4.4.12. The SRv6 Locator TLV
If the inside area supports SRv6, the Area Leader SHOULD copy all
SRv6 locator TLVs [I-D.ietf-lsr-isis-srv6-extensions] advertised by
Inside Routers to the Proxy LSP.
4.4.13. Traffic Engineering Information
If the inside area supports TE, the Area Leader SHOULD advertise a TE
Router ID TLV (134) [RFC5305] in the Proxy LSP. It SHOULD copy the
Shared Risk Link Group (SRLS) TLVs (138) [RFC5307] advertised by
Inside Edge Routers about links to Outside Edge Routers.
If the inside area supports IPv6 TE, the Area Leader SHOULD advertise
an IPv6 TE Router ID TLV (140) [RFC6119] in the Proxy LSP. It SHOULD
also copy the IPv6 SRLG TLVs (139) [RFC6119] advertised by Inside
Edge Routers about links to Outside Edge Routers.
5. Inside Edge Router Functions
The Inside Edge Router has two additional and important functions.
First, it MUST generate IIHs that appear to have come from the Area
Proxy System Identifier. Second, it MUST filter the L2 LSPs, Partial
Sequence Number PDUs (PSNPs), and Complete Sequence Number PDUs
(CSNPs) that are being advertised to Outside Routers.
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5.1. Generating L2 IIHs to Outside Routers
The Inside Edge Router has one or more Level 2 interfaces to Outside
Routers. These may be identified by explicit configuration or by the
fact that they are not also Level 1 circuits. On these Level 2
interfaces, the Inside Edge Router MUST NOT send an IIH until it has
learned the Area Proxy System Id from the Area Leader. Then, once it
has learned the Area Proxy System Id, it MUST generate its IIHs on
the circuit using the Proxy System Id as the source of the IIH.
Using the Proxy System Id causes the Outside Router to advertise an
adjacency to the Proxy System Id, not to the Inside Edge Router,
which supports the proxy function. The normal system id of the
Inside Edge Router MUST NOT be used as it will cause unnecessary
adjacencies to form and subsequently flap.
5.2. Filtering LSP information
For the proxy abstraction to be effective the L2 LSPs generated by
the Inside Routers MUST be restricted to the Inside Area. The Inside
Routers know which system ids are members of the Inside Area based on
the Level 1 LSDB. To prevent unwanted LSP information from escaping
the Inside Area, the Inside Edge Router MUST perform filtering of LSP
flooding, CSNPs, and PSNPs. Specifically:
A Level 2 LSP with a source system identifier that is found in the
Level 1 LSDB MUST never be flooded to an Outside Router.
A Level 2 CSNP sent to an Outside Router MUST NOT contain any
information about an LSP with a system identifier found in the
Level 1 LSDB. If an Inside Edge Router filters a CSNP and there
is no remaining content, then the CSNP MUST NOT be sent. The
source address of the CSNP MUST be the Area Proxy System Id.
A Level 2 PSNP sent to an Outside Router MUST NOT contain any
information about an LSP with a system identifier found in the
Level 1 LSDB. If an Inside Edge Router filters a PSNP and there
is no remaining content, then the PSNP MUST NOT be sent. The
source address of the PSNP MUST be the Area Proxy System Id.
6. Acknowledgments
The authors would like to thank Bruno Decraene, Vivek Ilangovan, and
Gunter Van De Velde for their many helpful comments. The authors
would also like to thank a small group that wishes to remain
anonymous for their valuable contributions.
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7. IANA Considerations
This memo requests that IANA allocate and assign one code point from
the IS-IS TLV Codepoints registry for the Area Segment SID TLV (XXX),
one code point for the Area Proxy TLV (YYY), and one code point for
the Inside Node TLV (ZZZ). The registry fields for all three should
be: IIH:n, LSP:y, SNP:n, Purge:n.
In association with this, this memo requests that IANA create a
registry for code points for the sub-TLVs of the Area Proxy TLV.
Name of the registry: Sub-TLVs for TLV YYY (Area Proxy TLV)
Required information for registrations: Temporary registrations
may be made under the Early IANA Allocation of Standards Track
Code Points policy. [RFC7120] Permanent registrations require the
publication of an RFC describing the usage of the code point.
Applicable registration policy: RFC Required and Expert Review.
We propose the initial experts be Chris Hopps, Tony Li, and Sarah
Chen.
Size, format, and syntax of registry entries: Value (0-255), Name,
and Reference
Initial assignments and reservations: IANA is requested to assign
the following code points:
+-------+------------------------------+---------------+
| Value | Name | Reference |
+-------+------------------------------+---------------+
| AAA | Area Proxy System Identifier | This document |
| BBB | Area Segment SID | This document |
+-------+------------------------------+---------------+
IANA is also requested to allocate and assign one code point from the
IS-IS Router Capability TLV sub-TLV registry for the Area Proxy
Capability (LLL).
8. Security Considerations
This document introduces no new security issues. Security of routing
within a domain is already addressed as part of the routing protocols
themselves. This document proposes no changes to those security
architectures.
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9. References
9.1. Normative References
[I-D.ietf-lsr-dynamic-flooding]
Li, T., Psenak, P., Ginsberg, L., Chen, H., Przygienda,
T., Cooper, D., Jalil, L., Dontula, S., and G. Mishra,
"Dynamic Flooding on Dense Graphs", draft-ietf-lsr-
dynamic-flooding-07 (work in progress), June 2020.
[I-D.ietf-lsr-isis-srv6-extensions]
Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
Z. Hu, "IS-IS Extension to Support Segment Routing over
IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-08
(work in progress), April 2020.
[ISO10589]
International Organization for Standardization,
"Intermediate System to Intermediate System Intra-Domain
Routing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network
Service (ISO 8473)", ISO/IEC 10589:2002, Nov. 2002.
[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>.
[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>.
[RFC5301] McPherson, D. and N. Shen, "Dynamic Hostname Exchange
Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301,
October 2008, <https://www.rfc-editor.org/info/rfc5301>.
[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>.
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[RFC5307] Kompella, K., Ed. and Y. Rekhter, Ed., "IS-IS Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 5307, DOI 10.17487/RFC5307, October 2008,
<https://www.rfc-editor.org/info/rfc5307>.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
DOI 10.17487/RFC5308, October 2008,
<https://www.rfc-editor.org/info/rfc5308>.
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
February 2011, <https://www.rfc-editor.org/info/rfc6119>.
[RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions
for Advertising Router Information", RFC 7981,
DOI 10.17487/RFC7981, October 2016,
<https://www.rfc-editor.org/info/rfc7981>.
[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>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
[RFC8491] Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
"Signaling Maximum SID Depth (MSD) Using IS-IS", RFC 8491,
DOI 10.17487/RFC8491, November 2018,
<https://www.rfc-editor.org/info/rfc8491>.
[RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C.,
Bashandy, A., Gredler, H., and B. Decraene, "IS-IS
Extensions for Segment Routing", RFC 8667,
DOI 10.17487/RFC8667, December 2019,
<https://www.rfc-editor.org/info/rfc8667>.
9.2. Informative References
[Clos] Clos, C., "A Study of Non-Blocking Switching Networks",
The Bell System Technical Journal Vol. 32(2), DOI
10.1002/j.1538-7305.1953.tb01433.x, March 1953,
<http://dx.doi.org/10.1002/j.1538-7305.1953.tb01433.x>.
[RFC7120] Cotton, M., "Early IANA Allocation of Standards Track Code
Points", BCP 100, RFC 7120, DOI 10.17487/RFC7120, January
2014, <https://www.rfc-editor.org/info/rfc7120>.
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9.3. URIs
[1] https://tools.ietf.org/html/bcp14
Authors' Addresses
Tony Li
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
USA
Email: tony.li@tony.li
Sarah Chen
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
USA
Email: sarahchen@arista.com
Vivek Ilangovan
Arista Networks
5453 Great America Parkway
Santa Clara, California 95054
USA
Email: ilangovan@arista.com
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Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring
,
MD 20904
United States of America
Phone:
301 502-1347
Email:
gyan.s.mishra@verizon.com
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