draft-ietf-lsr-isis-extended-hierarchy-00.txt   draft-ietf-lsr-isis-extended-hierarchy-01.txt 
Internet Engineering Task Force T. Li Internet Engineering Task Force T. Li
Internet-Draft Arista Networks Internet-Draft Arista Networks
Intended status: Standards Track L. Ginsberg Intended status: Standards Track L. Ginsberg
Expires: May 2, 2020 P. Wells Expires: July 11, 2020 P. Wells
Cisco Systems Cisco Systems
October 30, 2019 January 8, 2020
IS-IS Extended Hierarchy IS-IS Extended Hierarchy
draft-ietf-lsr-isis-extended-hierarchy-00 draft-ietf-lsr-isis-extended-hierarchy-01
Abstract Abstract
The IS-IS routing protocol was originally defined with a two level The IS-IS routing protocol was originally defined with a two level
hierarchical structure. This was adequate for the networks at the hierarchical structure. This was adequate for the networks at the
time. As we continue to expand the scale of our networks, it is time. As we continue to expand the scale of our networks, it is
apparent that additional hierarchy would be a welcome degree of apparent that additional hierarchy would be a welcome degree of
flexibility in network design. flexibility in network design.
This document defines IS-IS Levels 3 through 8. This document defines IS-IS Levels 3 through 8.
skipping to change at page 1, line 38 skipping to change at page 1, line 38
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 May 2, 2020. This Internet-Draft will expire on July 11, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 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.
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. PDU changes . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. PDU changes . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Circuit Type . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Circuit Type . . . . . . . . . . . . . . . . . . . . . . 4
2.2. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 4 2.2. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Additional PDUs . . . . . . . . . . . . . . . . . . . . . . . 4 3. Additional PDUs . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Level n LAN IS to IS hello PDU (Ln-LAN-HELLO-PDU) . . . . 4 3.1. Level n LAN IS to IS hello PDU (Ln-LAN-HELLO-PDU) . . . . 5
3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO- 3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO-
PDU) . . . . . . . . . . . . . . . . . . . . . . . . . . 5 PDU) . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Level Specific Area Identifiers . . . . . . . . . . . . . . . 5 4. Level Specific Area Identifiers . . . . . . . . . . . . . . . 5
4.1. IS-IS Area Identifier TLV . . . . . . . . . . . . . . . . 5 4.1. IS-IS Area Hierarchy TLV . . . . . . . . . . . . . . . . 6
4.2. Adjacency Formation Rules . . . . . . . . . . . . . . . . 6 4.2. Adjacency Formation Rules . . . . . . . . . . . . . . . . 8
4.2.1. Level 3-8 Adjacency Formation Rules . . . . . . . . . 7 4.2.1. Level 3-8 Adjacency Formation Rules . . . . . . . . . 8
4.2.2. Special Level-2 Adjacency Formation Rules . . . . . . 7 4.2.2. Special Level-1 and Level-2 Adjacency Formation Rules 9
5. New Flooding Scopes . . . . . . . . . . . . . . . . . . . . . 7 4.2.2.1. Actions on a Point-to-Point Circuit . . . . . . . 9
6. MAC Addresses . . . . . . . . . . . . . . . . . . . . . . . . 8 4.2.2.2. Actions on a LAN Circuit . . . . . . . . . . . . 9
7. Inheritance of TLVs . . . . . . . . . . . . . . . . . . . . . 9 4.2.2.3. Reporting of Mismatched Area Hierarchies . . . . 9
8. Behavior of Level n . . . . . . . . . . . . . . . . . . . . . 9 5. New Flooding Scopes . . . . . . . . . . . . . . . . . . . . . 10
9. Relationship between levels . . . . . . . . . . . . . . . . . 9 6. MAC Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9 7. Inheritance of TLVs . . . . . . . . . . . . . . . . . . . . . 13
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9 8. Behavior of Level n . . . . . . . . . . . . . . . . . . . . . 13
11.1. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 9 9. Relationship between levels . . . . . . . . . . . . . . . . . 13
11.2. New PDUs . . . . . . . . . . . . . . . . . . . . . . . . 10 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13
11.3. New TLVs . . . . . . . . . . . . . . . . . . . . . . . . 10 11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
11.4. New Flooding Scopes . . . . . . . . . . . . . . . . . . 10 11.1. PDU Type . . . . . . . . . . . . . . . . . . . . . . . . 13
11.5. New MAC Addresses . . . . . . . . . . . . . . . . . . . 11 11.2. New PDUs . . . . . . . . . . . . . . . . . . . . . . . . 13
12. Security Considerations . . . . . . . . . . . . . . . . . . . 12 11.3. New TLVs . . . . . . . . . . . . . . . . . . . . . . . . 14
13. Normative References . . . . . . . . . . . . . . . . . . . . 12 11.4. New Flooding Scopes . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12 11.5. New MAC Addresses . . . . . . . . . . . . . . . . . . . 15
12. Security Considerations . . . . . . . . . . . . . . . . . . . 16
13. Normative References . . . . . . . . . . . . . . . . . . . . 16
Appendix A. Preventing Cross Branching in the Hierarchy . . . . 16
Appendix B. Guidelines for Introducing a new level . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18
1. Introduction 1. Introduction
The IS-IS routing protocol IS-IS [ISO10589] currently supports a two The IS-IS routing protocol IS-IS [ISO10589] currently supports a two
level hierarchy of abstraction. The fundamental unit of abstraction level hierarchy of abstraction. The fundamental unit of abstraction
is the 'area', which is a (hopefully) connected set of systems is the 'area', which is a (hopefully) connected set of systems
running IS-IS at the same level. Level 1, the lowest level, is 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. abstracted by routers that participate in both Level 1 and Level 2.
Practical considerations, such as the size of an area's link state Practical considerations, such as the size of an area's link state
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makes sense to expand the design for the future. makes sense to expand the design for the future.
The modifications described herein are designed to be fully backward The modifications described herein are designed to be fully backward
compatible and have no effect on existing networks. The compatible and have no effect on existing networks. The
modifications are also designed to have no effect whatsoever on modifications are also designed to have no effect whatsoever on
networks that only use Level 1 and/or Level 2. networks that only use Level 1 and/or Level 2.
Section references in this document are references to sections of IS- Section references in this document are references to sections of IS-
IS [ISO10589]. IS [ISO10589].
Note that [ISO10589] uses a bit encoding convention where bit numbers
are 1 based and Bit 1 is the Least Significant Bit (LSB) of the
datatype. Traditionally IETF documents have used a bit encoding
convention where bit numbers are 0 based and Bit 0 is the Most
Significant Bit (MSB) of the datatype. This document uses [ISO10589]
conventions throughout.
1.1. Requirements Language 1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
document are to be interpreted as described in RFC 2119 [RFC2119]. "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.
2. PDU changes 2. PDU changes
In this section, we enumerate all of the redefinitions of protocol In this section, we enumerate all of the redefinitions of protocol
header fields necessary to add additional levels. header fields necessary to add additional levels.
2.1. Circuit Type 2.1. Circuit Type
In the fixed header of some IS-IS PDUs, a field is named 'Reserved/ In the fixed header of some IS-IS PDUs, a field is named 'Reserved/
Circuit Type' (Section 9.5). The high order six bits are reserved, Circuit Type' (Section 9.5). The high order six bits are reserved,
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IANA) IANA)
Level 5 (L5-LAN-HELLO-PDU): 35 (Suggested - to be assigned by Level 5 (L5-LAN-HELLO-PDU): 35 (Suggested - to be assigned by
IANA) IANA)
Level 6 (L6-LAN-HELLO-PDU): 36 (Suggested - to be assigned by Level 6 (L6-LAN-HELLO-PDU): 36 (Suggested - to be assigned by
IANA) IANA)
Level 7 (L7-LAN-HELLO-PDU): 37 (Suggested - to be assigned by Level 7 (L7-LAN-HELLO-PDU): 37 (Suggested - to be assigned by
IANA) IANA)
Level 8 (L8-LAN-HELLO-PDU): 38 (Suggested - to be assigned by Level 8 (L8-LAN-HELLO-PDU): 38 (Suggested - to be assigned by
IANA) IANA)
The Circuit Type field MUST be set to indicate all levels supported The Circuit Type field MUST be set to indicate all levels supported
on that circuit. on that circuit - not just the level associated with the containing
PDU type.
3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO-PDU) 3.2. Level n Point-to-point IS to IS hello PDU (Ln-P2P-HELLO-PDU)
The 'Point-to-point IS to IS hello PDU' (Section 9.7) is used on The 'Point-to-point IS to IS hello PDU' (Section 9.7) is used on
Level 1 and Level 2 circuits. Legacy systems will not expect the Level 1 and Level 2 circuits. Legacy systems will not expect the
circuit type field to indicate other levels, so a new PDU is used if circuit type field to indicate other levels, so a new PDU is used if
the circuit supports other levels. The additional PDU is the 'Level the circuit supports other levels. The additional PDU is the 'Level
n Point-to-point IS to IS hello PDU' (Ln-P2P-HELLO-PDU) and has PDU n Point-to-point IS to IS hello PDU' (Ln-P2P-HELLO-PDU) and has PDU
Type 39 (Suggested - to be assigned by IANA). The format of this PDU Type 39 (Suggested - to be assigned by IANA). The format of this PDU
is identical to the existing Point-to-Point IS to IS hello PDU. Both is identical to the existing Point-to-Point IS to IS hello PDU. Both
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[ISO10589] defines an Area Address to uniquely identify a Level-1 [ISO10589] defines an Area Address to uniquely identify a Level-1
area. A given area may have multiple synonymous area addresses - area. A given area may have multiple synonymous area addresses -
which is useful in support of hitless merging or splitting of areas. which is useful in support of hitless merging or splitting of areas.
Area address matching is part of the adjacency formation rules Area address matching is part of the adjacency formation rules
defined in Section 8 which determine whether a given adjacency defined in Section 8 which determine whether a given adjacency
supports Level-1, Level-2, or both. Area addresses are advertised in supports Level-1, Level-2, or both. Area addresses are advertised in
IIHs and LSPs using the Area Address TLV. IIHs and LSPs using the Area Address TLV.
With the extensions defined in this document, there is a need to With the extensions defined in this document, there is a need to
define an equivalent identifier for Levels 2-8. This identifier is a define an equivalent identifier for Levels 2-8. The Level Specific
32 bit value and is advertised using the new Area Identifier TLV Area Identifier (LSAI) is a 16 bit value and is advertised using the
defined in the following section. There is no relationship between new Area Hierarchy TLV defined in Section 4.1. There is no
the Level-1 Area Addresses and the new Level Specific Area relationship between a Level-1 Area Address and an LSAI.
Identifier.
Just as with Area Addresses, multiple synonomous Area Identifiers may Just as with Area Addresses, multiple synonomous LSAIs may be
be assigned to a given level. This supports hitless merging or assigned to a given level. This supports hitless merging or
splitting of the level specific area. Although it is legal to do so, splitting of the level specific area. Although it is legal to do so,
it is generally not useful to define more than two Area Identifiers it is generally not useful to define more than two Area Identifiers
for a given level. for a given level.
4.1. IS-IS Area Identifier TLV A node MAY support any set of contiguous levels. Support for non-
contiguous levels is undefined.
The Area Identifier TLV is added to IS-IS to allow nodes to indicate 4.1. IS-IS Area Hierarchy TLV
which areas they participate in for Levels 2-8. Area Identifiers are
locally administered 32 bit numbers. Each level may have multiple
Area Identifiers. The format of the TLV is:
0 1 2 3 The Area Hierarchy TLV specifies the set of LSAIs which comprise the
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 branch of the network hierarchy to which the advertising node is
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ connected. The TLV MUST include at least one LSAI for Levels 2-N,
| TLV Type | TLV Length | Level | Count | where N is >= 2 and N represents the highest level supported in the
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IS-IS domain. It is RECOMMENDED that N == 8 even when not all 8
| Area Identifier | levels are currently in use, but in cases where a network does not
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ support higher levels a number less than 8 MAY be used.
TLV Type: ZZZ Note that the levels advertised MAY include levels which are not
supported by the advertising node.
TLV Length: ( 2 * number of Levels) + ( 4 * each Count field ) The Area Hierarchy TLV has the following format:
Level: The level number of the area. (1 octet) Legal values are 8 7 6 5 4 3 2 1
2-8 +-+-+-+-+-+-+-+-+
| TLV Type |
+-+-+-+-+-+-+-+-+
| TLV Length |
+-+-+-+-+-+-+-+-+
| Supp-Levels |
+-+-+-+-+-+-+-+-+
Count: The number of Area Identifier fields (1 octet) Followed by one or more Level Specific Area ID Sets:
Area Identifier: One or more identifiers associated with the area. 1 0
(4 * count octets) 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Level | # of LSAIs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Level Specific Area Id(s) |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Level/Count/Area Identifier tuple MAY be repeated as necessary. TLV Type: ZZZ (1 octet)
The Area Identifier TLV MAY appear in all types of IIHs except for TLV Length: Variable (1 octet)
Level 1 LAN IS to IS hellos.
The Area Identifier TLV MAY appear in LSP #0 of non-pseudo-node Level Supp-Levels: A contiguous bitmask representing the set of levels
3-8 Flooding Scoped LSPs defined in Section 5. It MUST NOT be supported by the advertising node (1 octet)
present in any LSP with non-zero LSP number. If present in an LSP Bit #8 of this field is set if Level 8 is supported.
with non-zero LSP number it MUST be ignored on receipt. Bit #7 of this field is set if Level 7 is supported.
Bit #6 of this field is set if Level 6 is supported.
Bit #5 of this field is set if Level 5 is supported.
Bit #4 of this field is set if Level 4 is supported.
Bit #3 of this field is set if Level 3 is supported.
Bit #2 of this field is set if Level 2 is supported.
Bit #1 of this field is set if Level 1 is supported
A system may participate in more than one level. At a given level, If the Supp-level bit mask is non-contiguous all advertised LSAIs
an area may have a number of synonymous identifiers. A system MUST are ignored.
advertise all of the levels it supports and the associated Area
Identifiers. Each Level Specific Area ID Set consists of:
Level: 2-8 (1 octet)
# of LSAI: >=1 (1 octet)
LSAIs: The set of synonomous LSAIs associated with this level
(2 * # of LSAIs octets)
The Area Hierarchy TLV MUST appear in all new IIH PDUs defined in
Section 3. It MAY appear in P2P-HELLO-PDUs, L1-LAN-HELLO-PDUs, or
L2-LAN-HELLO-PDUs.
The Area Hierarchy TLV MUST appear in LSP #0 of non-pseudo-node Level
3-8 Flooding Scoped LSPs defined in Section 5. It MAY appear in L1
or L2 LSP #0. It MUST NOT be present in any LSP with non-zero LSP
number. If present in an LSP with non-zero LSP number it MUST be
ignored on receipt.
Multiple Area Hierarchy TLVs MUST NOT be sent. In the event multiple
Area Hierarchy TLVs are received, the first such TLV in the PDU is
used. Subsequent TLVs in the same PDU MUST be ignored.
4.2. Adjacency Formation Rules 4.2. Adjacency Formation Rules
Adjacency formation rules for Levels 1 and 2 are defined in Adjacency formation rules for Levels 1 and 2 are defined in
[ISO10589] and are not altered by these extensions except where noted [ISO10589] and are not altered by these extensions except where noted
below. below.
Adjacency Formation rules for Levels 3 and above are defined to Adjacency Formation rules for Levels 3 and above are defined to
insure that adjacency support for a given level is only enabled when insure that adjacency support for a given level is only enabled when
there is a matching Area Identifier. Adjacency formation rules also there is a matching Area Identifier. Adjacency formation rules also
are defined so as to prevent interconnection of neighbors which will are defined so as to prevent interconnection of neighbors which will
connect to different areas at levels above any supported level. connect to different areas at levels above any supported level.
4.2.1. Level 3-8 Adjacency Formation Rules The checks discussed below need to be performed on receipt of an IIH.
When the Area Identifier TLV appears in a Level N Point-to-point IS 4.2.1. Level 3-8 Adjacency Formation Rules
to IS hello PDU or a Level N LAN IS to IS Hello PDU, the Circuit Type
field is inspected. For all levels with their corresponding bit set
in the Circuit Type in the range 3-8 the following checks are
performed:
o Check for a matching Area Identifier at the same level The Area Hierarchy TLV MUST be present in a Level N Point-to-point IS
to IS hello PDU or a Level N LAN IS to IS Hello PDU and the TLV
content MUST adhere to the definition in Section 4.1. Beginning with
the lowest level supported by the receiving node on this circuit and
including all higher levels for which the receiver has an assigned
LSAI regardless as to whether the higher levels are supported on this
circuit, the set of LSAIs defined on the receiving node is compared
against the set of LSAIs advertised in the received TLV. A matching
LSAI MUST be found for each level.
o Check for a matching Area Identifier at all supported levels If all of the checks pass then a new adjacency is formed or an
greater than the level being checked existing adjacency is maintained.
If both checks pass, then an adjacency can be formed supporting the NOTE: The absence of the advertisement of an LSAI for a given level
level. If any of the checks fail, then that level MUST NOT be is considered as a failure to find a matching LSAI.
supported by an adjacency formed on that circuit.
On a Point-to-Point circuit, a single adjacency is formed which On a Point-to-Point circuit, a single adjacency is formed which
supports all of the levels which pass the above checks. supports all of the levels supported by both nodes on this circuit.
On a LAN circuit, an adjacency is formed only for the level specified On a LAN circuit, an adjacency is formed supporting only the level
by the PDU type. Nevertheless, the checks for all levels with the specified by the PDU type.
corresponding bit set in the Circuit Type MUST be performed.
Note that (as previously specified) the set of levels supported MUST Note that (as previously specified) the set of levels advertised MUST
be contiguous. be contiguous.
4.2.2. Special Level-2 Adjacency Formation Rules 4.2.2. Special Level-1 and Level-2 Adjacency Formation Rules
The Area Identifier TLV MAY appear in a Point-to-point IS to IS hello The Area Hierarchy TLV MAY appear in a Point-to-point IS to IS hello
PDU or Level 2 LAN IS to IS Hello PDU (both specified in [ISO10589]). PDU, Level 1 LAN IS to IS Hello PDU, or Level 2 LAN IS to IS Hello
In such a case, the neighbor may or may not support the Area PDU (PDUs specified in [ISO10589]). In such a case, the neighbor may
Identifier TLV. If the Area Identifier TLV is present and Level 2 is or may not support the Area Hierarchy TLV. The following sub-
indicated as being supported in the Circuit Type field, then in sections define modified adjacency formation rules for point-to-point
addition to the checks specified in [ISO10589] the checks specified and LAN circuits.
in the previous section SHOULD be performed for Level 2.
4.2.2.1. Actions on a Point-to-Point Circuit
If the Area Hierarchy TLV is present, then in addition to the checks
specified in [ISO10589] the checks specified in Section 4.2.1 MUST be
performed for all levels for which the receiver has an assigned LSAI
beginning with Level 2. If those checks fail an adjacency MUST NOT
be formed and any existing matching adjacency MUST transition to DOWN
state.
4.2.2.2. Actions on a LAN Circuit
Adjacency formation MUST follow the rules defined in [ISO10589]. If
the Area Hierarchy TLV is present in the Level 1 or Level 2 LAN IS to
IS Hello PDU then the checks specified in Section 4.2.1 SHOULD be
performed for all levels for which the receiver has an assigned LSAI
beginning with Level 2. If those checks fail an error SHOULD be
reported, but the level specific adjacency is still allowed. This
prevents violation of the assumption of transitivity on the LAN in
the presence of systems which do not support the extensions defined
in this document.
4.2.2.3. Reporting of Mismatched Area Hierarchies
When forming adjacencies at Level-1 and/or Level-2, it is possible to
have a mixture of legacy nodes (which do NOT support the extensions
defined in this document) and new nodes which do support the
extensions.
In Point-to-Point mode, legacy nodes will not advertise the new Area
Hierarchy TLV and will not have an assigned LSAI for Level-2. It
then becomes possible for new nodes with mismatched Area Hierarchies
to form adjacencies with legacy nodes and form an L1 or L2 area where
not all new nodes have a matching Area Hierarchy. This cannot be
detected when forming adjacencies if the new nodes are not directly
connected - but it can be detected after the adjacencies have been
formed by inspecting the set of Area Hierarchy TLVs in the level
specific LSPs of all routers in the area.
Similarly in LAN mode, the transitivity requirement means that new
nodes MUST form adjacencies with all nodes connected to the LAN even
when the Area Hierarchy TLV mismatch check fails (see
Section 4.2.2.2). This can occur both at Level-1 and Level-2.
New nodes MUST report these inconsistencies.
5. New Flooding Scopes 5. New Flooding Scopes
For levels 3-8, all link state information, PSNPs, and CSNPs are For levels 3-8, all link state information, PSNPs, and CSNPs are
relayed in conformance with RFC 7356 [RFC7356]. Additional flooding relayed in conformance with [RFC7356]. Additional flooding scopes
scopes are defined for each new level, for both circuit flooding are defined for each new level, for both circuit flooding scope and
scope and level flooding scope. Level flooding scopes are defined level flooding scope. Level flooding scopes are defined for both
for both Standard and Extended TLV formats. The list of additional Standard and Extended TLV formats. The list of additional flooding
flooding scopes is: scopes is:
FS LSP ID Format/ FS LSP ID Format/
Value Description TLV Format Value Description TLV Format
----- ------------------------------ ----------------- ----- ------------------------------ -----------------
6 Level 3 Circuit Flooding Scope Extended/Standard 6 Level 3 Circuit Flooding Scope Extended/Standard
7 Level 4 Circuit Flooding Scope Extended/Standard 7 Level 4 Circuit Flooding Scope Extended/Standard
8 Level 5 Circuit Flooding Scope Extended/Standard 8 Level 5 Circuit Flooding Scope Extended/Standard
9 Level 6 Circuit Flooding Scope Extended/Standard 9 Level 6 Circuit Flooding Scope Extended/Standard
10 Level 7 Circuit Flooding Scope Extended/Standard 10 Level 7 Circuit Flooding Scope Extended/Standard
11 Level 8 Circuit Flooding Scope Extended/Standard 11 Level 8 Circuit Flooding Scope Extended/Standard
skipping to change at page 8, line 39 skipping to change at page 11, line 39
73 Level 6 Circuit Flooding Scope Extended/Extended 73 Level 6 Circuit Flooding Scope Extended/Extended
74 Level 7 Circuit Flooding Scope Extended/Extended 74 Level 7 Circuit Flooding Scope Extended/Extended
75 Level 8 Circuit Flooding Scope Extended/Extended 75 Level 8 Circuit Flooding Scope Extended/Extended
76 Level 3 Flooding Scope Extended/Extended 76 Level 3 Flooding Scope Extended/Extended
77 Level 4 Flooding Scope Extended/Extended 77 Level 4 Flooding Scope Extended/Extended
78 Level 5 Flooding Scope Extended/Extended 78 Level 5 Flooding Scope Extended/Extended
79 Level 6 Flooding Scope Extended/Extended 79 Level 6 Flooding Scope Extended/Extended
80 Level 7 Flooding Scope Extended/Extended 80 Level 7 Flooding Scope Extended/Extended
81 Level 8 Flooding Scope Extended/Extended 81 Level 8 Flooding Scope Extended/Extended
The final octet of the header of a Flooding Scoped LSP as defined in
[RFC7356] contains Reserved/LSPDBOL/IS Type information. This field
is redefined for the new flooding scopes defined in this document as
follows:
Reserved/ATT/LSPDBOL
Bits 8-5 Reserved
Transmitted as 0 and ignored on receipt
Bit 4 ATT
If set to 1 indicates that the sending IS is attached to
routers in other Level N areas via Level N+1
Bit 3 LSDBOL
As defined in RFC7356
Bits 2-1
Transmitted as 0 and ignored on receipt.
Note that the levels supported (analogous to the IS-type information
in L1 and L2 LSPs) can be obtained from the Area Hierarchy TLV
advertised in the associated LSP #0.
Note that the definition of the ATT bit specified above also applies
to L2 LSPs. Previously this bit would have no meaning as [ISO10589]
does not define support for Level 3.
6. MAC Addresses 6. MAC Addresses
On a broadcast network, PDUs are currently sent to the AllL1Iss or On a broadcast network, PDUs are currently sent to the AllL1Iss or
AllL2Iss MAC addresses. We will need additional MAC addresses for AllL2Iss MAC addresses. We will need additional MAC addresses for
Levels 3-8. Levels 3-8.
AllL3ISs: MAC3 AllL3ISs: MAC3
AllL4ISs: MAC4 AllL4ISs: MAC4
skipping to change at page 9, line 37 skipping to change at page 13, line 29
9. Relationship between levels 9. Relationship between levels
The relationship between Level n and Level n-1 is analogous to the The relationship between Level n and Level n-1 is analogous to the
relationship between Level 2 and Level 1. relationship between Level 2 and Level 1.
An area at Level n has at most one parent at Level n+1. An area at Level n has at most one parent at Level n+1.
10. Acknowledgements 10. Acknowledgements
The authors would like to thank Dinesh Dutt for inspiring this The authors would like to thank Dinesh Dutt for inspiring this
document and Huaimo Chen for his comments. document and Huaimo Chen for his comments. The authors would also
like to thank Tony Pryzienda for his careful review and excellent
suggestions.
11. IANA Considerations 11. IANA Considerations
This document makes many requests to IANA, as follows: This document makes many requests to IANA, as follows:
11.1. PDU Type 11.1. PDU Type
The existing IS-IS PDU registry currently supports values 0-31. This The existing IS-IS PDU registry currently supports values 0-31. This
should be expanded to support the values 0-255. The existing value should be expanded to support the values 0-255. The existing value
assignments should be retained. Value 255 should be reserved. assignments should be retained. Value 255 should be reserved.
skipping to change at page 10, line 29 skipping to change at page 14, line 17
L8-LAN-HELLO-PDU: 38 (Suggested - to be assigned by IANA) L8-LAN-HELLO-PDU: 38 (Suggested - to be assigned by IANA)
Ln-P2P-HELLO-PDU: 39 (Suggested - to be assigned by IANA) Ln-P2P-HELLO-PDU: 39 (Suggested - to be assigned by IANA)
11.3. New TLVs 11.3. New TLVs
IANA is requested to allocate values from the IS-IS TLV registry for IANA is requested to allocate values from the IS-IS TLV registry for
the following: the following:
Area Identifier: ZZZ Area Hierarchy: ZZZ
11.4. New Flooding Scopes 11.4. New Flooding Scopes
IANA is requested to allocate the following values from the IS-IS IANA is requested to allocate the following values from the IS-IS
Flooding Scope Identifier Registry. Flooding Scope Identifier Registry.
FS LSP ID Format/ IIH Announce FS LSP ID Format/ IIH Announce
Value Description TLV Format Lx-P2P Lx-LAN Value Description TLV Format Lx-P2P Lx-LAN
----- ------------------------------ ----------------- ------ ------ ----- ------------------------------ ----------------- ------ ------
6 Level 3 Circuit Flooding Scope Extended/Standard Y Y 6 Level 3 Circuit Flooding Scope Extended/Standard Y Y
skipping to change at page 12, line 37 skipping to change at page 16, line 37
[RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation [RFC5309] Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation
over LAN in Link State Routing Protocols", RFC 5309, over LAN in Link State Routing Protocols", RFC 5309,
DOI 10.17487/RFC5309, October 2008, DOI 10.17487/RFC5309, October 2008,
<https://www.rfc-editor.org/info/rfc5309>. <https://www.rfc-editor.org/info/rfc5309>.
[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding [RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356, Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014, DOI 10.17487/RFC7356, September 2014,
<https://www.rfc-editor.org/info/rfc7356>. <https://www.rfc-editor.org/info/rfc7356>.
[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>.
Appendix A. Preventing Cross Branching in the Hierarchy
The use of additional levels requires careful interconnection of
routers which support multiple levels. Consistent association of
LSAIs is required not only for validating the connections between
routers in a level specific area but also for all levels above a
given level to which any of the routers may be connected (directly or
indirectly). Failure to do so can result in interconnecting
different branches of a tree leading to interarea loops. This leads
to the requirement that all routers advertise an LSAI for all levels
regardless of whether a given router is configured to participate in
a given level or not.
At first glance it may seem that it would be sufficient for each
router to advertise LSAIs only for the levels that the router is
configured to support. However, the following simple example
illustrates why this is problematic.
+------------+ +------------+ +------------+
| Rtr A | | Rtr B | | Rtr C |
| L3 Area 30 |---| L3 Area 30 |---| L3 Area 30 |
| L4 Area 40 | | | | L4 Area 44 |
+------------+ +------------+ +------------+
Since Router B does not support Level 4, it chose not to advertise
any Area for Level 4. This means that neither Router A nor Router C
can tell by inspecting hellos that not all routers in Level 3 area 30
have been configured to support the same Level 4 area. It is
possible for Rtr A and Rtr C to discover the LSAIs advertised by all
routers by inspecting the Level 3 LSPs - however this requires that
Level 3 adjacencies be formed and maintained even when routing cannot
be safely performed via all adjacencies in a given area. It then
needs to be decided how routing over existing adjacencies should be
limited. A number of possibilities exist:
Treat the area as if it were two partitions. In the example
Router A would be in one partition and Router C would be in
another partition. But Router B could belong to either partition.
Select a winning Level 4 Area among the set of Level 4 areas
advertised in L3 LSPs and only allow leaking of routes to/from
that level
But either of these options introduce the possibility that a
previously fully connected hierarchy becomes partially disconnected
as a result of a single configuration change on a single router and/
or the bringup of a new router.
The choice made was then to require all routers suppporting the
extensions in this document to advertise an LSAI for all levels
regardless of what specific levels an individual router is configured
to support. This guarantees that any inconsistency between the
intended connectivity of a router at all levels - direct and indirect
- can be detected during exchange of hellos and therefore adjacency
bringup can always be blocked when necessary.
Appendix B. Guidelines for Introducing a new level
It is desirable to be able to introduce support for a new level
without disruption. This section discusses ways to do this.
Initial deployment may require only the support of one additional
level (Level 3). However, in the future increased network scale may
make introduction of an additional level (Level 4) desirable. It is
suggested that all routers be configured to advertise a single
candidate LSAI for Level 4 - for the purposes of the example let's
use LSAI 44. When ready to deploy Level 4, it is then only necessary
to enable Level 4 on those routers who will be participating in the
additional level.
However, perhaps at the time of deploying Level 3 the administrator
has no idea what LSAI will be used for Level 4 in the future. In
such a case a "dummy" LSAI should be configured for Level 4 on all
routers - let's use "0" in this example. In this case, what needs to
be done when ready to enable Level 4 is to go to every router
(regardless of whether it will actively participate in the new level)
and configure the intended LSAI for Level 4. If LSAI 45 is the
intended Level 4 area, then LSAI 45 is configured on each router.
Each router is then advertising two LSAIs for Level 4: (0, 45). Once
this is completed, go to every router and remove the "dummy" Level 4
LSAI (0) and the network is now ready to have this Level 4 area
enabled.
In the event that support for a new level needs to be introduced and
no LSAI was ever advertised for that level, the introduction of LSAI
for the new level will cause temporary adjacency flaps as the
advertisement of the LSAI for the new level is introduced. To avoid
this, implementations would need to introduce support for temporary
disablement of the LSAI check for the new level until the
configuration of the new LSAI is complete on all nodes. Support for
this transition mode is outside the scope of this document. The need
for a transition mode can be avoided if an LSAI is configured for
levels 2-8 from day one.
Authors' Addresses Authors' Addresses
Tony Li Tony Li
Arista Networks Arista Networks
5453 Great America Parkway 5453 Great America Parkway
Santa Clara, California 95054 Santa Clara, California 95054
United States of America United States of America
Email: tony.li@tony.li Email: tony.li@tony.li
Les Ginsberg Les Ginsberg
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