Internet DRAFT - draft-ietf-isis-fs-lsp
draft-ietf-isis-fs-lsp
Networking Working Group L. Ginsberg
Internet-Draft S. Previdi
Intended status: Standards Track Y. Yang
Expires: December 6, 2014 Cisco Systems
June 4, 2014
IS-IS Flooding Scope LSPs
draft-ietf-isis-fs-lsp-02.txt
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 wide scope or
domain wide scope. There are existing use cases where support of
other flooding scopes are desirable. This document defines new
Protocol Data Units (PDUs) which 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 TLVs and sub-TLVs which 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.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://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."
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This Internet-Draft will expire on December 6, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Extended TLVs . . . . . . . . . . . . . . . . . . . . . . . . 4
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 . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Definition of New PDUs . . . . . . . . . . . . . . . . . . . 6
3.1. Flooding Scoped LSP Format . . . . . . . . . . . . . . . 6
3.2. Flooding Scoped CSNP Format . . . . . . . . . . . . . . . 9
3.3. Flooding Scope PSNP Format . . . . . . . . . . . . . . . 10
4. Flooding Scope Update Process Operation . . . . . . . . . . . 12
4.1. Scope Types . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Operation on Point-to-Point Circuits . . . . . . . . . . 12
4.3. Operation on Broadcast Circuits . . . . . . . . . . . . . 13
4.4. Use of Authentication . . . . . . . . . . . . . . . . . . 13
4.5. Priority Flooding . . . . . . . . . . . . . . . . . . . . 13
5. Deployment Considerations . . . . . . . . . . . . . . . . . . 14
6. Graceful Restart Interactions . . . . . . . . . . . . . . . . 14
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7. Multi-instance Interactions . . . . . . . . . . . . . . . . . 14
8. Circuit Scoped Flooding . . . . . . . . . . . . . . . . . . . 14
9. Extending LSP Set Capacity . . . . . . . . . . . . . . . . . 15
10. Domain Scoped Flooding . . . . . . . . . . . . . . . . . . . 16
11. Announcing Support for Flooding Scopes . . . . . . . . . . . 17
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
13. Security Considerations . . . . . . . . . . . . . . . . . . . 19
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 20
15. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
15.1. Normative References . . . . . . . . . . . . . . . . . . 20
15.2. Informational References . . . . . . . . . . . . . . . . 21
Appendix A. Change History . . . . . . . . . . . . . . . . . . . 21
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
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 Protocol Data Units (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 sub-domain. 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 which the
Update Process currently provides for L1 and L2 scopes. This
document defines these new PDUs and the modified Update Process rules
which are to be used in supporting new flooding scopes.
New deployment cases have introduced the need for reliable and
efficient circuit scoped flooding. For example, Appointed Forwarder
information as defined in [RFC7176] needs to be flooded reliably and
efficiently to all RBridges on a broadcast circuit. Currently, only
Intermediate System to Intermediate System 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 scoped 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 [RFC5311] that the set of LSPs that
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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. [RFC5311]
has defined a backwards compatible protocol extension which can be
used to overcome this limitation if needed. While the [RFC5311]
solution is viable, in order to be interoperable with routers which
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. As the introduction of new PDUs
required to support new flooding scopes is by definition not
interoperable with legacy routers, it is 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 (Type/Length/Value) are encoded using an eight
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 which 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. The possible PDU types supported by the protocol are
therefore 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.
2. Extended TLVs
Standard TLVs as defined in [IS-IS] as well as standard sub-TLVs
(first introduced in [RFC5305]) have an eight 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 which 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 which 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.
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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
Scoped PDUs which have a flooding scope designated for their use
(defined later in this document)
o A given flooding scope supports the use of either 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/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
o Use of extended TLVs and extended sub-TLVs does not alter in any
way the maximum size of PDUs which 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 eight bit type is encoded as an unsigned 16 bit integer where
the 8 MSBs are all 0
o The eight bit length field is replaced by the 16 bit length field
o The length MAY take on values greater than 255
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3. Definition of New PDUs
In support of new flooding scopes the following new PDUs are
required:
o Flooding Scoped LSPs (FS-LSPs)
o Flooding Scoped Complete Sequence Number PDUs (FS-CSNPs)
o Flooding Scoped 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. The maximum area addresses checks
specified in [IS-IS] are therefore not performed on FS PDUs.
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
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+-------------------------+
| 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]
PDU Type - 10 (Subject to assignment by IANA) 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 TLV 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
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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
+-------------------------+
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 Source ID to 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 which are allowed in an FS-LSP are specific to
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the defined scope.
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]
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PDU Type - 11 (Subject to assignment by IANA) 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-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 Numbers 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 which are allowed in an FS-CSNP are
limited to those TLVs which are supported by standard CSNP.
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 |
+-------------------------+
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| 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 (Subject to assignment by IANA) 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-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 TLV and
extended sub-TLVs.
PDU Length - Entire Length of this PDU, in octets, including
the header.
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Source ID - the system ID of the Intermediate System
(with zero Circuit ID) generating this Sequence Numbers PDU
Variable Length Fields which are allowed in an FS-PSNP are
limited to those TLVs which 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. There is therefore 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 are limited to those circuits which 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.
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 sub-domain scope).
Additional scopes may be defined which include all circuits enabled
for either L1 or L2 routing (domain-wide 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
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state. 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 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], [RFC6822], and
[RFC6325].
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 which 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.
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 LSP/CSNP/PSNP PDUs 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 which 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.
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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 PDUs 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. Therefore all routers in
the flooding domain for a given scope SHOULD support both FS PDUs and
the specified scope before use of that scope can be enabled.
The U bit in FS-PSNPs provides a means to suppress retransmissions of
unsupported scopes. Routers which 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 which is unsupported. Routers which 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.
6. Graceful Restart Interactions
[RFC5306] 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 [RFC5306] for
further details.
7. Multi-instance Interactions
In cases where FS-PDUs are associated with a non-zero instance the
use of IID-TLVs in FS-PDUs follows the rules for use in LSPs, CSNPs,
PSNPs as defined in [RFC6822].
8. Circuit Scoped Flooding
This document defines four circuit scoped 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
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o Extended Level 1 circuit scope (E-L1CS) - this uses extended TLVs
and extended sub-TLVs
o Extended Level 2 circuit scope (E-L1CS) - 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 scoped FS-LSPs consists of the set of FS-LSPs
which both have matching circuit scope and are transmitted (locally
generated) or received on a specific circuit.
The set of TLVs which may be included in such FS-LSPs is specific to
the given use case and is outside the scope of this document.
9. Extending LSP Set Capacity
The need for additional space in the set of LSPs generated by a
single IS has been articulated in [RFC5311]. 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 Scope (L1FS) - this uses standard TLVs and standard sub-
TLVs
o Level 2 Scope (L2FS) - this uses standard TLVs and standard sub-
TLVs
o Extended Level 1 Scope (E-L1FS) - this uses extended TLVs and
extended sub-TLVs
o Extended Level 2 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
64K of additional LSPs which may be generated by a single system at
each level.
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:
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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 set to be usable
o Information in an LxFS LSP (e.g. IS-Neighbor information) which
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 which 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.
10. Domain Scoped Flooding
Existing support for flooding information domain wide (i.e. to L1
routers in all areas as well as to routers in the Level 2 sub-domain)
requires the use of leaking procedures between levels. For further
details see [RFC4971]. This is sufficient when the data being
flooded domain-wide 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-wide flooding. FS-LSPs with this scope MUST be flooded on all
circuits regardless of what level(s) are supported on that circuit.
o Domain Scope (DSFS) - this uses standard TLVs and standard sub-
TLVs
o Extended Domain Scope (E-DSFS) - 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 scoped DSFS and
E-DSFS LSPs to advertise an identifier which 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.
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When IS-IS is deployed in support of Layer 3 routing for IPv4 and/or
IPv6 then FS-LSP #0 with domain-wide 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. [RFC6325]) only support a single area. Therefore
domain-wide scope is not yet applicable. When the Layer 2 standards
are updated to include multi-area support the identifiers which can
be used to support inter-area reachability will be defined - at which
point the use of domain-wide scope for Layer 2 can be fully defined.
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.
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Scoped Flooding Support
Type: 243 (suggested - to be assigned by IANA)
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-Point IIH L1, L2, domain-wide, and all circuit scopes
MAY be advertised.
In Level 1 LAN IIHs L1, domain-wide, and L1 circuit scopes MAY be
advertised. L2 scopes and L2 circuit scopes MUST NOT be advertised.
In Level 2 LAN IIHs L2, domain-wide, 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.
12. IANA Considerations
This document requires the definition of three new PDU types that
need to be reflected in the ISIS PDU registry. Values below are
suggested values subject to assignment by IANA.
Value Description
---- ---------------------
10 FS-LSP
11 FS-CSNP
12 FS-PSNP
This document requires that a new IANA registry be created to control
the assignment of scope identifiers in FS-PDUs. The registration
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procedure is "Expert Review" as defined in [RFC5226]. Suggested
registry name is "LSP Flooding Scoped Identifier Registry". A scope
identifier is a number from 1-127 inclusive. Values 1 - 63 are
reserved for PDUs which use standard TLVs and standard sub-TLVs.
Values 64 - 127 are reserved for PDUs which 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. Values
are suggested values subject to assignment by IANA.
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-wide 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-wide Flooding Scope Extended/Extended Y Y Y
(69-127) Unassigned
This document requires the definition of a new IS-IS TLV to be
reflected in the "IS-IS TLV Codepoints" registry:
Type Description IIH LSP SNP Purge
---- ------------ --- --- --- -----
243 Circuit Scoped Flooding Support Y N N N
The IANA TLV codepoints registry is 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.
13. Security Considerations
Security concerns for IS-IS are addressed in [IS-IS], [RFC5304], and
[RFC5310].
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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] "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, 29 June 2012.", 2012.
[IS-IS] "Intermediate system to Intermediate system intra-domain
routeing information exchange protocol for use in
conjunction with the protocol for providing the
connectionless-mode Network Service (ISO 8473), ISO/IEC
10589:2002, Second Edition.", Nov 2002.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4971] Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
System to Intermediate System (IS-IS) Extensions for
Advertising Router Information", RFC 4971, July 2007.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5304] Li, T. and R. Atkinson, "IS-IS Cryptographic
Authentication", RFC 5304, October 2008.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, October 2008.
[RFC5306] Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
RFC 5306, October 2008.
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[RFC5310] Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
and M. Fanto, "IS-IS Generic Cryptographic
Authentication", RFC 5310, February 2009.
[RFC6822] Previdi, S., Ginsberg, L., Shand, M., Roy, A., and D.
Ward, "IS-IS Multi-Instance", RFC 6822, December 2012.
15.2. Informational References
[RFC5311] McPherson, D., Ginsberg, L., Previdi, S., and M. Shand,
"Simplified Extension of Link State PDU (LSP) Space for
IS-IS", RFC 5311, February 2009.
[RFC6325] Perlman, R., Eastlake, D., Dutt, D., Gai, S., and A.
Ghanwani, "Routing Bridges (RBridges): Base Protocol
Specification", RFC 6325, July 2011.
[RFC7176] 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.
Appendix A. Change History
Changes from 01 to 02 version
o Updated Section 11 to state what scopes MUST NOT be announced in a
given IIH PDU
o Updated IANA section for new "LSP Flooding Scoped Identifier
Registry" to include the hello PDUs in which a given scope may be
announced.
Authors' Addresses
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
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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, North Carolina 27709-4987
USA
Email: yiya@cisco.com
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