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IETF RFC 7356
Last modified on Wednesday, September 3rd, 2014
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Internet Engineering Task Force (IETF) L. Ginsberg
Request for Comments: 7356 S. Previdi
Category: Standards Track Y. Yang
ISSN: 2070-1721 Cisco Systems
September 2014
IS-IS Flooding Scope Link State PDUs (LSPs)
 Abstract
Intermediate System to Intermediate System (IS-IS) provides efficient
and reliable flooding of information to its peers; however, the
current flooding scopes are limited to either area scope or domain
scope. There are existing use cases where support of other flooding
scopes is desirable. This document defines new Protocol Data Units
(PDUs) that provide support for new flooding scopes as well as
additional space for advertising information targeted for the
currently supported flooding scopes. This document also defines
extended Type-Length-Values (TLVs) and sub-TLVs that are encoded
using 16-bit fields for Type and Length.
The protocol extensions defined in this document are not backwards
compatible with existing implementations and so must be deployed with
care.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/RFC 7356.
Ginsberg, et al. Standards Track PAGE 1 
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Ginsberg, et al. Standards Track PAGE 2
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 5
2. Extended TLVs . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Use of Extended TLVs and Extended Sub-TLVs . . . . . . . 5
2.2. Use of Standard Code Points in Extended TLVs and Extended
Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Definition of New PDUs . . . . . . . . . . . . . . . . . . . 6
3.1. Flooding Scoped LSP Format . . . . . . . . . . . . . . . 7
3.2. Flooding Scoped CSNP Format . . . . . . . . . . . . . . . 10
3.3. Flooding Scope PSNP Format . . . . . . . . . . . . . . . 12
4. Flooding Scope Update Process Operation . . . . . . . . . . . 13
4.1. Scope Types . . . . . . . . . . . . . . . . . . . . . . . 14
4.2. Operation on Point-to-Point Circuits . . . . . . . . . . 14
4.3. Operation on Broadcast Circuits . . . . . . . . . . . . . 14
4.4. Use of Authentication . . . . . . . . . . . . . . . . . . 15
4.5. Priority Flooding . . . . . . . . . . . . . . . . . . . . 15
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 15
6. Graceful Restart Interactions . . . . . . . . . . . . . . . . 16
7. Multi-instance Interactions . . . . . . . . . . . . . . . . . 16
8. Circuit Scope Flooding . . . . . . . . . . . . . . . . . . . 16
9. Extending LSP Set Capacity . . . . . . . . . . . . . . . . . 17
10. Domain Scope Flooding . . . . . . . . . . . . . . . . . . . . 18
11. Announcing Support for Flooding Scopes . . . . . . . . . . . 19
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
13. Security Considerations . . . . . . . . . . . . . . . . . . . 21
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
15.1. Normative References . . . . . . . . . . . . . . . . . . 21
15.2. Informative References . . . . . . . . . . . . . . . . . 22
1. Introduction
The Update Process, as defined by [IS-IS], provides reliable and
efficient flooding of information to all routers in a given flooding
scope. Currently, the protocol supports two flooding scopes and
associated PDUs. Level 1 (L1) Link State PDUs (LSPs) are flooded to
all routers in an area. Level 2 (L2) LSPs are flooded to all routers
in the Level 2 subdomain. The basic operation of the Update Process
can be applied to any subset of the routers in a given topology so
long as that topology is not partitioned. It is, therefore, possible
to introduce new PDUs in support of other flooding scopes and utilize
the same Update Process machinery to provide the same reliability and
efficiency that the Update Process currently provides for L1 and L2
scopes. This document defines these new PDUs and the modified Update
Process rules that are to be used in supporting new flooding scopes.
Ginsberg, et al. Standards Track PAGE 3
RFC 7356 IS-IS Flooding Scope LSPs September 2014
New deployment cases have introduced the need for reliable and
efficient circuit scope flooding. For example, Appointed Forwarder
information, as defined in [RFC 7176], needs to be flooded reliably
and efficiently to all Routing Bridges (RBridges) on a broadcast
circuit. Currently, only IS-IS Hellos (IIHs) have the matching scope
-- but IIHs are unreliable, i.e., individual IIHs may be lost without
affecting correct operation of the protocol. To provide reliability
in cases where the set of information to be flooded exceeds the
carrying capacity of a single PDU requires sending the information
periodically even when no changes in the content have occurred. When
the information content is large, this is inefficient and still does
not provide a guarantee of reliability. This document defines
circuit scope flooding in order to provide a solution for such cases.
Another existing limitation of [IS-IS] is the carrying capacity of an
LSP set. It has been noted in [RFC 5311] that the set of LSPs that
may be originated by a system at each level is limited to 256 LSPs,
and the maximum size of each LSP is limited by the minimum Maximum
Transmission Unit (MTU) of any link used to flood LSPs. [RFC 5311]
has defined a backwards-compatible protocol extension that can be
used to overcome this limitation if needed. While the [RFC 5311]
solution is viable, in order to be interoperable with routers that do
not support the extension, it imposes some restrictions on what can/
cannot be advertised in the Extended LSPs and requires allocation of
multiple unique system IDs to a given router. A more flexible and
less constraining solution is possible if interoperability with
legacy routers is not a requirement. By definition, the introduction
of new PDUs required to support new flooding scopes is not
interoperable with legacy routers. It is, therefore, possible to
simultaneously introduce an alternative solution to the limited LSP
set carrying capacity of Level 1 and Level 2 LSPs as part of the
extensions defined in this document. This capability is also defined
in this document.
Standard IS-IS TLVs are encoded using an 8-bit type and an 8-bit
length. In cases where the set of information about a single object
exceeds 255 octets, multiple TLVs are required to encode all of the
relevant information. This document introduces extended TLVs and
extended sub-TLVs that use a 16-bit Type field and a 16-bit Length
field.
The PDU Type field in the common header for all IS-IS PDUs is a 5-bit
field. Therefore, possible PDU types supported by the protocol are
limited to a maximum of 32. In order to minimize the need to
introduce additional PDU types in the future, the new PDUs introduced
in this document are defined so as to allow multiple flooding scopes
to be associated with the same PDU type. This means if new flooding
scopes are required in the future, the same PDU type can be used.
Ginsberg, et al. Standards Track PAGE 4
RFC 7356 IS-IS Flooding Scope LSPs September 2014
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 [RFC 2119].
2. Extended TLVs
Standard TLVs as defined in [IS-IS] as well as standard sub-TLVs
(first introduced in [RFC 5305]) have an 8-bit Type field and an
eight-bit Length field. This constrains the information included in
a single TLV or sub-TLV to 255 octets. With the increasing use of
sub-TLVs, it becomes more likely that the amount of information about
a single object that needs to be advertised may exceed 255 octets.
In such cases, the information is encoded in multiple TLVs. This
leads to less efficient encoding since the information that uniquely
identifies the object must be repeated in each TLV and requires
additional implementation complexity when receiving the information
to ensure that all information about the object is correctly
collected from the multiple TLVs.
This document introduces extended TLVs and extended sub-TLVs. These
are encoded using a 16-bit Type field and a 16-bit Length field.
2.1. Use of Extended TLVs and Extended Sub-TLVs
The following restrictions apply to the use of extended TLVs and
extended sub-TLVs:
o Extended TLVs and extended sub-TLVs are permitted only in Flooding
Scope PDUs that have a flooding scope designated for their use
(defined later in this document)
o A given flooding scope supports either the use of standard TLVs
and standard sub-TLVs or the use of extended TLVs and extended
sub-TLVs, but not both
o Extended TLVs and extended sub-TLVs MUST be used together, i.e.,
using Standard sub-TLVs within an Extended TLV or using Extended
sub-TLVs within a Standard TLV is invalid
o If additional levels of TLVs (e.g., sub-sub-TLVs) are introduced
in the future, then the size of the Type and Length fields in
these new sub-types MUST match the size used in the parent
o The 16-bit Type and Length fields are encoded in network byte
order
Ginsberg, et al. Standards Track PAGE 5
RFC 7356 IS-IS Flooding Scope LSPs September 2014
o Use of extended TLVs and extended sub-TLVs does not alter in any
way the maximum size of PDUs that may sent or received
2.2. Use of Standard Code Points in Extended TLVs and Extended Sub-TLVs
Standard TLV and standard sub-TLV code points as defined in the IANA
"IS-IS TLV Codepoints" registry MAY be used in extended TLVs and
extended sub-TLVs. Encoding is as specified for each of the standard
TLVs and standard sub-TLVs with the following differences:
o The 8-bit Type field is encoded as an unsigned 16-bit integer
where the 8 most significant bits (MSBs) are all 0
o The 8-bit Length field is replaced by the 16-bit Length field
o The length MAY take on values greater than 255
3. Definition of New PDUs
In support of new flooding scopes, the following new PDUs are
required:
o Flooding Scope LSPs (FS-LSPs)
o Flooding Scope Complete Sequence Number PDUs (FS-CSNPs)
o Flooding Scope Partial Sequence Number PDUs (FS-PSNPs)
Each of these PDUs is intentionally defined with a header as similar
in format as possible to the corresponding PDU types currently
defined in [IS-IS]. Although it might have been possible to
eliminate or redefine PDU header fields in a new way, the existing
formats are retained in order to allow maximum reuse of existing PDU
processing logic in an implementation.
Note that in the case of all FS PDUs, the Maximum Area Addresses
field in the header of the corresponding standard PDU has been
replaced with a Scope field. Therefore, maximum area addresses
checks specified in [IS-IS] are not performed on FS PDUs.
Ginsberg, et al. Standards Track PAGE 6
RFC 7356 IS-IS Flooding Scope LSPs September 2014
3.1. Flooding Scoped LSP Format
An FS-LSP has the following format:
No. of octets
+-------------------------+
| Intradomain Routeing | 1
| Protocol Discriminator |
+-------------------------+
| Length Indicator | 1
+-------------------------+
| Version/Protocol ID | 1
| Extension |
+-------------------------+
| ID Length | 1
+-------------------------+
|R|R|R| PDU Type | 1
+-------------------------+
| Version | 1
+-------------------------+
| Reserved | 1
+-------------------------+
|P| Scope | 1
+-------------------------+
| PDU Length | 2
+-------------------------+
| Remaining Lifetime | 2
+-------------------------+
| FS LSP ID | ID Length + 2
+-------------------------+
| Sequence Number | 4
+-------------------------+
| Checksum | 2
+-------------------------+
|Reserved|LSPDBOL|IS Type | 1
+-------------------------+
: Variable-Length Fields : Variable
+-------------------------+
Intradomain Routeing Protocol Discriminator: 0x83 (as defined in
[IS-IS]).
Length Indicator: Length of the fixed header in octets.
Version/Protocol ID Extension: 1
ID Length: As defined in [IS-IS].
Ginsberg, et al. Standards Track PAGE 7
RFC 7356 IS-IS Flooding Scope LSPs September 2014
PDU Type: 10 - Format as defined in [IS-IS].
Version: 1
Reserved: Transmitted as zero, ignored on receipt.
Scope: Bits 1-7 define the flooding scope.
The value 0 is reserved and MUST NOT be used. Received FS-LSPs
with a scope of 0 MUST be ignored and MUST NOT be flooded.
P: Bit 8 - Priority Bit. If set to 1, this LSP SHOULD be
flooded at high priority.
Scopes (1 - 63) are reserved for use with standard TLVs and
standard sub-TLVs.
Scopes (64 - 127) are reserved for use with extended TLVs and
extended sub-TLVs.
PDU Length: Entire length of this PDU, in octets, including the
header.
Remaining Lifetime: Number of seconds before this FS-LSP is
considered expired.
FS LSP ID: The system ID of the source of the FS-LSP. One of the
following two formats is used:
FS LSP ID Standard Format
+-------------------------+
| Source ID | ID Length
+-------------------------+
| Pseudonode ID | 1
+-------------------------+
| FS LSP Number | 1
+-------------------------+
FS LSP ID Extended Format
+-------------------------+
| Source ID | ID Length
+-------------------------+
| Extended FS LSP Number | 2
+-------------------------+
Ginsberg, et al. Standards Track PAGE 8
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Which format is used is specific to the scope and MUST be defined
when the specific flooding scope is defined.
Sequence Number: Sequence number of this FS-LSP.
Checksum: Checksum of contents of FS-LSP from the Source ID to the
end. Checksum is computed as defined in [IS-IS].
Reserved/LSPDBOL/IS Type
Bits 4-8 are reserved, which means they are transmitted as 0
and ignored on receipt.
LSPDBOL: Bit 3 - A value of 0 indicates no FS-LSP Database
Overload and a value of 1 indicates that the FS-LSP Database is
overloaded. The overload condition is specific to FS-LSPs with
the scope specified in the Scope field.
IS Type: Bits 1 and 2. The type of Intermediate System as
defined in [IS-IS].
Variable-length fields that are allowed in an FS-LSP are specific
to the defined scope.
Ginsberg, et al. Standards Track PAGE 9
RFC 7356 IS-IS Flooding Scope LSPs September 2014
3.2. Flooding Scoped CSNP Format
An FS-CSNP has the following format:
No. of octets
+-------------------------+
| Intradomain Routeing | 1
| Protocol Discriminator |
+-------------------------+
| Length Indicator | 1
+-------------------------+
| Version/Protocol ID | 1
| Extension |
+-------------------------+
| ID Length | 1
+-------------------------+
|R|R|R| PDU Type | 1
+-------------------------+
| Version | 1
+-------------------------+
| Reserved | 1
+-------------------------+
|R| Scope | 1
+-------------------------+
| PDU Length | 2
+-------------------------+
| Source ID | ID Length + 1
+-------------------------+
| Start FS-LSP ID | ID Length + 2
+-------------------------+
| End FS-LSP ID | ID Length + 2
+-------------------------+
: Variable-Length Fields : Variable
+-------------------------+
Intradomain Routeing Protocol Discriminator: 0x83 (as defined in
[IS-IS]).
Length Indicator: Length of the fixed header in octets.
Version/Protocol ID Extension: 1
ID Length: As defined in [IS-IS].
PDU Type: 11 - Format as defined in [IS-IS].
Version: 1
Ginsberg, et al. Standards Track PAGE 10
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Reserved: Transmitted as zero, ignored on receipt.
Scope: Bits 1-7 define the flooding scope.
The value 0 is reserved and MUST NOT be used. Received FS-
CSNPs with a scope of 0 MUST be ignored.
Bit 8 is Reserved, which means it is transmitted as 0 and
ignored on receipt.
Scopes (1 - 63) are reserved for use with standard TLVs and
standard sub-TLVs.
Scopes (64 - 127) are reserved for use with extended TLV and
extended sub-TLVs.
PDU Length: Entire length of this PDU, in octets, including the
header.
Source ID: The system ID of the Intermediate System (with zero
Circuit ID) generating this Sequence Number's PDU.
Start FS-LSP ID: The FS-LSP ID of the first FS-LSP with the
specified scope in the range covered by this FS-CSNP.
End FS-LSP ID: The FS-LSP ID of the last FS-LSP with the specified
scope in the range covered by this FS-CSNP.
Variable-length fields that are allowed in an FS-CSNP are limited
to those TLVs that are supported by standard CSNP.
Ginsberg, et al. Standards Track PAGE 11
RFC 7356 IS-IS Flooding Scope LSPs September 2014
3.3. Flooding Scope PSNP Format
An FS-PSNP has the following format:
No. of octets
+-------------------------+
| Intradomain Routeing | 1
| Protocol Discriminator |
+-------------------------+
| Length Indicator | 1
+-------------------------+
| Version/Protocol ID | 1
| Extension |
+-------------------------+
| ID Length | 1
+-------------------------+
|R|R|R| PDU Type | 1
+-------------------------+
| Version | 1
+-------------------------+
| Reserved | 1
+-------------------------+
|U| Scope | 1
+-------------------------+
| PDU Length | 2
+-------------------------+
| Source ID | ID Length + 1
+-------------------------+
: Variable-Length Fields : Variable
+-------------------------+
Intradomain Routeing Protocol Discriminator: 0x83 (as defined in
[IS-IS]).
Length Indicator: Length of the fixed header in octets.
Version/Protocol ID Extension: 1
ID Length: As defined in [IS-IS].
PDU Type: 12 - Format as defined in [IS-IS].
Version: 1
Reserved: Transmitted as zero, ignored on receipt.
Ginsberg, et al. Standards Track PAGE 12
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Scope: Bits 1-7 define the flooding scope.
The value 0 is reserved and MUST NOT be used. Received FS-
PSNPs with a scope of 0 MUST be ignored.
U: Bit 8 - A value of 0 indicates that the specified flooding
scope is supported. A value of 1 indicates that the specified
flooding scope is unsupported. When U = 1, variable-length
fields other than authentication MUST NOT be included in the
PDU.
Scopes (1 - 63) are reserved for use with standard TLVs and
standard sub-TLVs.
Scopes (64 - 127) are reserved for use with extended TLVs and
extended sub-TLVs.
PDU Length: Entire length of this PDU, in octets, including the
header.
Source ID: The system ID of the Intermediate System (with zero
Circuit ID) generating this Sequence Number's PDU.
Variable-length fields that are allowed in an FS-PSNP are limited
to those TLVs that are supported by standard PSNPs.
4. Flooding Scope Update Process Operation
The Update Process, as defined in [IS-IS], maintains a Link State
Database (LSDB) for each level supported. Each level-specific LSDB
contains the full set of LSPs generated by all routers operating in
that level-specific scope. The introduction of FS-LSPs creates
additional LSDBs (FS-LSDBs) for each additional scope supported. The
set of FS-LSPs in each FS-LSDB consists of all FS-LSPs generated by
all routers operating in that scope. Therefore, there is an
additional instance of the Update Process for each supported flooding
scope.
Operation of the scope-specific Update Process follows the Update
Process specification in [IS-IS]. The circuit(s) on which FS-LSPs
are flooded is limited to those circuits that are participating in
the given scope. Similarly, the sending/receiving of FS-CSNPs and
FS-PSNPs is limited to the circuits participating in the given scope.
Consistent support of a given flooding scope on a circuit by all
routers operating on that circuit is required.
Ginsberg, et al. Standards Track PAGE 13
RFC 7356 IS-IS Flooding Scope LSPs September 2014
4.1. Scope Types
A flooding scope may be limited to a single circuit (circuit scope).
Circuit scopes may be further limited by level (L1 Circuit Scope / L2
Circuit Scope).
A flooding scope may be limited to all circuits enabled for L1
routing (area scope).
A flooding scope may be limited to all circuits enabled for L2
routing (L2 subdomain scope).
Additional scopes may be defined that include all circuits enabled
for either L1 or L2 routing (domain scope).
4.2. Operation on Point-to-Point Circuits
When a new adjacency is formed, synchronization of all FS-LSDBs
supported on that circuit is required; therefore, FS-CSNPs for all
supported scopes MUST be sent when a new adjacency reaches the UP
state. The Send Receive Message (SRM) bit MUST be set for all
FS-LSPs associated with the scopes supported on that circuit.
Receipt of an FS-PSNP with the U bit equal to 1 indicates that the
neighbor does not support that scope (although it does support FS
PDUs). This MUST cause the SRM bit to be cleared for all FS-LSPs
with the matching scope, which are currently marked for flooding on
that circuit.
4.3. Operation on Broadcast Circuits
FS PDUs are sent to the same destination address(es) as standard PDUs
for the given protocol instance. For specification of the defined
destination addresses, consult [IS-IS], [IEEEaq], [RFC 6822], and
[RFC 6325].
The Designated Intermediate System (DIS) for a broadcast circuit has
the responsibility to generate periodic scope-specific FS-CSNPs for
all supported scopes. A scope-specific DIS is NOT elected as all
routers on a circuit MUST support a consistent set of flooding
scopes.
It is possible that a scope may be defined that is not level
specific. In such a case, the DIS for each level enabled on a
broadcast circuit MUST independently send FS PDUs for that scope to
the appropriate level-specific destination address. This may result
in redundant flooding of FS-LSPs for that scope.
Ginsberg, et al. Standards Track PAGE 14
RFC 7356 IS-IS Flooding Scope LSPs September 2014
4.4. Use of Authentication
Authentication TLVs MAY be included in FS PDUs. When authentication
is in use, the scope is first used to select the authentication
configuration that is applicable. The authentication check is then
performed as normal. Although scope-specific authentication MAY be
used, sharing of authentication among multiple scopes and/or with the
standard LSPs/CSNPs/PSNPs is considered sufficient.
4.5. Priority Flooding
When the FS LSP ID Extended format is used, the set of LSPs generated
by an IS may be quite large. It may be useful to identify those LSPs
in the set that contain information of higher priority. Such LSPs
will have the P bit set to 1 in the Scope field in the LSP header.
Such LSPs SHOULD be flooded at a higher priority than LSPs with the P
bit set to 0. This is a suggested behavior on the part of the
originator of the LSP. When an LSP is purged, the original state of
the P bit MUST be preserved.
5. Deployment Considerations
Introduction of new PDU types is incompatible with legacy
implementations. Legacy implementations do not support the
FS-specific Update process(es) and, therefore, flooding of the
FS-LSPs throughout the defined scope is unreliable when not all
routers in the defined scope support FS PDUs. Further, legacy
implementations will likely treat the reception of an FS PDU as an
error. Even when all routers in a given scope support FS PDUs, if
not all routers in the flooding domain for a given scope support that
scope, then flooding of the FS-LSPs may be compromised. When
deploying a new flooding scope, correct operation therefore requires
that both FS PDUs and the new scope be supported by all routers in
the flooding domain of the new scope.
The U bit in FS-PSNPs provides a means to suppress retransmissions of
unsupported scopes. Routers that support FS PDUs SHOULD support the
sending of PSNPs with the U bit equal to 1 when an FS-LSP is received
with a scope that is unsupported. Routers that support FS PDUs
SHOULD trigger management notifications when FS PDUs are received for
unsupported scopes and when PSNPs with the U bit equal to 1 are
received.
Ginsberg, et al. Standards Track PAGE 15
RFC 7356 IS-IS Flooding Scope LSPs September 2014
6. Graceful Restart Interactions
[RFC 5306] defines protocol extensions in support of graceful restart
of a routing instance. Synchronization of all supported FS-LSDBs is
required in order for database synchronization to be complete. This
involves the use of additional T2 timers. Receipt of a PSNP with the
U bit equal to 1 will cause FS-LSDB synchronization with that
neighbor to be considered complete for that scope. See [RFC 5306] for
further details.
7. Multi-instance Interactions
In cases where FS-PDUs are associated with a non-zero instance, the
use of Instance Identifier TLVs (IID-TLVs) in FS-PDUs follows the
rules for use in LSPs, CSNPs, and PSNPs as defined in [RFC 6822].
8. Circuit Scope Flooding
This document defines four circuit scope flooding identifiers:
o Level 1 Circuit Scope (L1CS) -- this uses standard TLVs and
standard sub-TLVs
o Level 2 Circuit Scope (L2CS) -- this uses standard TLVs and
standard sub-TLVs
o Extended Level 1 Circuit Scope (E-L1CS) -- this uses extended TLVs
and extended sub-TLVs
o Extended Level 2 Circuit Scope (E-L2CS) -- this uses extended TLVs
and extended sub-TLVs
FS-LSPs with the Scope field set to one of these values contain
information specific to the circuit on which they are flooded. When
received, such FS-LSPs MUST NOT be flooded on any other circuit. The
FS LSP ID Extended format is used in these PDUs. The FS-LSDB
associated with circuit scope FS-LSPs consists of the set of FS-LSPs
that both have matching circuit scopes and are transmitted (locally
generated) or received on a specific circuit.
The set of TLVs that may be included in such FS-LSPs is specific to
the given use case and is outside the scope of this document.
Ginsberg, et al. Standards Track PAGE 16
RFC 7356 IS-IS Flooding Scope LSPs September 2014
9. Extending LSP Set Capacity
The need for additional space in the set of LSPs generated by a
single IS has been articulated in [RFC 5311]. When legacy
interoperability is not a requirement, the use of FS-LSPs meets that
need without requiring the assignment of alias system-ids to a single
IS. Four flooding scopes are defined for this purpose:
o Level 1 Flooding Scope (L1FS) -- this uses standard TLVs and
standard sub-TLVs
o Level 2 Flooding Scope (L2FS) -- this uses standard TLVs and
standard sub-TLVs
o Extended Level 1 Flooding Scope (E-L1FS) -- this uses extended
TLVs and extended sub-TLVs
o Extended Level 2 Flooding Scope (E-L2FS) -- this uses extended
TLVs and extended sub-TLVs
L1FS and E-L1FS LSPs are flooded on all L1 circuits. L2FS and E-L2FS
LSPs are flooded on all L2 circuits.
The FS LSP ID Extended format is used in these PDUs. This provides
64 K of additional LSPs that may be generated by a single system at
each level.
LxFS and E-LxFS LSPs are used by the level-specific Decision Process
(defined in [IS-IS]) in the same manner as standard LSPs (i.e., as
additional information sourced by the same IS) subject to the
following restrictions:
o A valid version of standard LSP #0 from the same IS at the
corresponding level MUST be present in the LSDB in order for the
LxFS/E-LxFS set to be usable.
o Information in an LxFS of E-LxFS LSP (e.g., IS-Neighbor
information) that supports using the originating IS as a transit
node MUST NOT be used when the Overload bit is set in the
corresponding standard LSP #0.
o TLVs that are restricted to standard LSP #0 MUST NOT appear in
LxFS LSPs.
There are no further restrictions as to what TLVs may be advertised
in FS-LSPs.
Ginsberg, et al. Standards Track PAGE 17
RFC 7356 IS-IS Flooding Scope LSPs September 2014
10. Domain Scope Flooding
Existing support for flooding information throughout a domain (i.e.,
to L1 routers in all areas as well as to routers in the Level 2
subdomain) requires the use of leaking procedures between levels.
For further details, see [RFC 4971]. This is sufficient when the data
being flooded throughout the domain consists of individual TLVs. If
it is desired to retain the identity of the originating IS for the
complete contents of a PDU, then support for flooding the unchanged
PDU is desirable. This document, therefore, defines two flooding
scopes in support of domain flooding. FS-LSPs with this scope MUST
be flooded on all circuits regardless of what level(s) is supported
on that circuit.
o Domain Flooding Scope (DFS) -- this uses standard TLVs and
standard sub-TLVs
o Extended Domain Flooding Scope (E-DFS) -- this uses extended TLVs
and extended sub-TLVs
The FS LSP ID Extended format is used in these PDUs.
Use of information in FS-LSPs for a given scope depends on
determining the reachability to the IS originating the FS-LSP. This
presents challenges for FS-LSPs with domain scopes because no single
IS has the full view of the topology across all areas. It is,
therefore, necessary for the originator of domain scope DSFS and
E-DSFS LSPs to advertise an identifier that will allow an IS who
receives such an FS-LSP to determine whether the source of the FS-LSP
is currently reachable. The identifier required depends on what
"address-families" are being advertised.
When IS-IS is deployed in support of Layer 3 routing for IPv4 and/or
IPv6, then FS-LSP #0 with domain scope MUST include at least one of
the following TLVs:
o IPv4 Traffic Engineering Router ID (TLV 134)
o IPv6 Traffic Engineering Router ID (TLV 140)
When IS-IS is deployed in support of Layer 2 routing, current
standards (e.g., [RFC 6325]) only support a single area. Therefore,
domain scope is not yet applicable. When the Layer 2 standards are
updated to include multi-area support, the identifiers that can be
used to support inter-area reachability will be defined -- at which
point the use of domain scope for Layer 2 can be fully defined.
Ginsberg, et al. Standards Track PAGE 18
RFC 7356 IS-IS Flooding Scope LSPs September 2014
11. Announcing Support for Flooding Scopes
Announcements of support for flooding scope may be useful in
validating that full support has been deployed and/or in isolating
the reasons for incomplete flooding of FS-LSPs for a given scope.
ISs supporting FS-PDUs MAY announce supported scopes in IIH PDUs. To
do so, a new TLV is defined.
Scope Flooding Support
Type: 243
Length: 1 - 127
Value
No. of octets
+----------------------+
|R| Supported Scope | 1
+----------------------+
: :
+----------------------+
|R| Supported Scope | 1
+----------------------+
A list of the circuit scopes supported on this circuit and other
non-circuit-flooding scopes supported.
R bit MUST be 0 and is ignored on receipt.
In a Point-to-Point IIH, L1, L2, domain, and all circuit scopes
MAY be advertised.
In Level 1 LAN IIHs, L1, domain, and L1 Circuit Scopes MAY be
advertised. L2 Scopes and L2 Circuit Scopes MUST NOT be
advertised.
In Level 2 LAN IIHs, L2, domain, and L2 Circuit Scopes MAY be
advertised. L1 Scopes and L1 Circuit Scopes MUST NOT be
advertised.
Information in this TLV MUST NOT be considered in adjacency
formation.
Whether information in this TLV is used to determine when FS-LSPs
associated with a locally supported scope are flooded is an
implementation choice.
Ginsberg, et al. Standards Track PAGE 19
RFC 7356 IS-IS Flooding Scope LSPs September 2014
12. IANA Considerations
This document includes the definition of three new PDU types that are
reflected in the "IS-IS PDU Registry".
Value Description
---- ---------------------
10 FS-LSP
11 FS-CSNP
12 FS-PSNP
A new IANA registry has been created to control the assignment of
scope identifiers in FS-PDUs. The registration procedure is "Expert
Review" as defined in [RFC 5226]. The registry name is "LSP Flooding
Scope Identifier Registry". A scope identifier is a number from
1-127, inclusive. Values 1 - 63 are reserved for PDUs that use
standard TLVs and standard sub-TLVs. Values 64 - 127 are reserved
for PDUs that use extended TLVs and extended sub-TLVs. The list of
Hello PDUs in which support for a given scope MAY be announced (using
Scope Flooding Support TLV) is specified for each defined scope.
The following scope identifiers are defined by this document.
FS LSP ID Format/ IIH Announce
Value Description TLV Format P2P L1LAN L2LAN
----- ------------------------------ ----------------- ---------------
1 Level 1 Circuit Flooding Scope Extended/Standard Y Y N
2 Level 2 Circuit Flooding Scope Extended/Standard Y N Y
3 Level 1 Flooding Scope Extended/Standard Y Y N
4 Level 2 Flooding Scope Extended/Standard Y N Y
5 Domain Flooding Scope Extended/Standard Y Y Y
(6-63)Unassigned
64 Level 1 Circuit Flooding Scope Extended/Extended Y Y N
65 Level 2 Circuit Flooding Scope Extended/Extended Y N Y
66 Level 1 Flooding Scope Extended/Extended Y Y N
67 Level 2 Flooding Scope Extended/Extended Y N Y
68 Domain Flooding Scope Extended/Extended Y Y Y
(69-127) Unassigned
The definition of a new IS-IS TLV is reflected in the "IS-IS TLV
Codepoints" registry:
Value Name IIH LSP SNP Purge
---- ------------ --- --- --- -----
243 Scope Flooding Support Y N N N
Ginsberg, et al. Standards Track PAGE 20
RFC 7356 IS-IS Flooding Scope LSPs September 2014
The IANA "IS-IS TLV Codepoints" registry has been extended to allow
definition of codepoints less than or equal to 65535. Codepoints
greater than 255 can only be used in PDUs designated to support
extended TLVs. This registry has also been updated to point to this
document as a reference (in addition to [RFC 3563] and [RFC 6233]).
13. Security Considerations
Security concerns for IS-IS are addressed in [IS-IS], [RFC 5304], and
[RFC 5310].
The new PDUs introduced are subject to the same security issues
associated with their standard LSP/CSNP/PSNP counterparts. To the
extent that additional PDUs represent additional load for routers in
the network, this increases the opportunity for denial-of-service
attacks.
14. Acknowledgements
The authors wish to thank Ayan Banerjee, Donald Eastlake, Hannes
Gredler, and Mike Shand for their comments.
15. References
15.1. Normative References
[IEEEaq] IEEE, "Standard for Local and metropolitan area networks
-- Media Access Control (MAC) Bridges and Virtual Bridged
Local Area Networks -- Amendment 20: Shortest Path
Bridging", IEEE Std 802.1aq-2012, June 2012.
[IS-IS] ISO/IEC 10589:2002, Second Edition, "Information
technology -- Telecommunications and information exchange
between systems -- Intermediate System to Intermediate
System intradomain routeing information exchange protocol
for use in conjunction with the protocol for providing the
connectionless-mode network service (ISO 8473)", 2002.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC 4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC 5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
Ginsberg, et al. Standards Track PAGE 21
RFC 7356 IS-IS Flooding Scope LSPs September 2014
[RFC 5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC 5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC 5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
RFC 5306, October 2008.
[RFC 5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC 6822] Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.
15.2. Informative References
[RFC 3563] Zinin, A., "Cooperative Agreement Between the ISOC/IETF
and ISO/IEC Joint Technical Committee 1/Sub Committee 6
(JTC1/SC6) on IS-IS Routing Protocol Development", RFC
3563, July 2003.
[RFC 5311] McPherson, D., Ginsberg, L., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for
IS-IS", RFC 5311, February 2009.
[RFC 6233] Li, T. and L. Ginsberg, "IS-IS Registry Extension for
Purges", RFC 6233, May 2011.
[RFC 6325] Perlman, R., Eastlake, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC 7176] Eastlake, D., Senevirathne, T., Ghanwani, A., Dutt, D.,
and A. Banerjee, "Transparent Interconnection of Lots of
Links (TRILL) Use of IS-IS", RFC 7176, May 2014.
Ginsberg, et al. Standards Track PAGE 22
RFC 7356 IS-IS Flooding Scope LSPs September 2014
Authors' Addresses
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
EMail: ginsberg@cisco.com
Stefano Previdi
Cisco Systems
Via Del Serafico 200
Rome 0144
Italy
EMail: sprevidi@cisco.com
Yi Yang
Cisco Systems
7100-9 Kit Creek Road
Research Triangle Park, NC 27709-4987
USA
EMail: yiya@cisco.com
Ginsberg, et al. Standards Track PAGE 23
RFC TOTAL SIZE: 46089 bytes
PUBLICATION DATE: Wednesday, September 3rd, 2014
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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