Internet DRAFT - draft-ginsberg-isis-prefix-attributes
draft-ginsberg-isis-prefix-attributes
Networking Working Group L. Ginsberg
Internet-Draft Cisco Systems
Intended status: Standards Track B. Decraene
Expires: September 3, 2015 Orange
C. Filsfils
Cisco Systems
S. Litkowski
Orange Business Service
S. Previdi
Cisco Systems
March 2, 2015
IS-IS Prefix Attributes for Extended IP and IPv6 Reachability
draft-ginsberg-isis-prefix-attributes-01.txt
Abstract
This document introduces new sub-TLVs to support advertisement of
prefix attribute flags and the source router id of the router which
originated a prefix advertisement.
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.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 3, 2015.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. New sub-TLVs for Extended Reachability TLVs . . . . . . . . . 3
2.1. IPv4/IPv6 Extended Reachability Attribute Flags . . . . . 3
2.2. IPv4/IPv6 Source Router ID . . . . . . . . . . . . . . . 5
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4. Security Considerations . . . . . . . . . . . . . . . . . . . 6
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Normative References . . . . . . . . . . . . . . . . . . 6
6.2. Informational References . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
There are existing use cases in which knowing additional attributes
of a prefix is useful. For example, it is useful to know whether an
advertised prefix is directly connected to the advertising router or
not. In the case of [SR] knowing whether a prefix is directly
connected or not determines what action should be taken as regards
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processing of labels associated with an incoming packet. Current
formats of the Extended Reachability TLVs for both IP and IPv6 are
fixed and do not allow the introduction of additional flags without
backwards compatibility issues. Therefore a new sub-TLV is
introduced which allows for the advertisement of attribute flags
associated with prefix advertisements.
It is also useful to know the source of a prefix advertisement when
the advertisement has been leaked to another level. Therefore a new
sub-TLV is introduced to advertise the router-id of the originator of
a prefix advertisement.
2. New sub-TLVs for Extended Reachability TLVs
The following new sub-TLVs are introduced:
o IPv4/IPv6 Extended Reachability Attributes
o IPv4 Source Router ID
o IPv6 Source Router ID
All sub-TLVs are applicable to TLVs 135, 235, 236, and/or 237.
2.1. IPv4/IPv6 Extended Reachability Attribute Flags
This sub-TLV supports the advertisement of additional flags
associated with a given prefix advertisement. The behavior of each
flag when a prefix advertisement is leaked from one level to another
(upwards or downwards) is explicitly defined below.
All flags are applicable to TLVs 135, 235, 236, 237 unless otherwise
stated.
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Prefix Attribute Flags
Type: 4 (suggested - to be assigned by IANA)
Length: Number of octets to follow
Value
(Length * 8) bits.
0 1 2 3 4 5 6 7...
+-+-+-+-+-+-+-+-+...
|X|R|N| ...
+-+-+-+-+-+-+-+-+...
Bits are defined/sent starting with Bit #0 defined below. Additional
bit definitions which may be defined in the future SHOULD be assigned
in ascending bit order so as to minimize the number of bits which
will need to be transmitted.
Undefined bits SHOULD be transmitted as 0 and MUST be
ignored on receipt.
Bits which are NOT transmitted MUST be treated as if they are
set to 0 on receipt.
X-Flag: External Prefix Flag (Bit 0)
Set if the prefix has been redistributed from another protocol.
This includes the case where multiple virtual routers are
supported and the source of the redistributed prefix is another
IS-IS instance.
The flag is preserved when leaked between levels.
In TLVs 236 and 237 this flag SHOULD always be sent as 0 and
MUST be ignored on receipt. This is because there is an existing
X flag defined in the fixed format of these TLVs as specified in
[RFC5308] and [RFC5120].
R-Flag: Re-advertisement Flag (Bit 1)
Set when the prefix has been leaked from one level to another
(upwards or downwards).
N-flag: Node Flag (Bit 2)
Set when the prefix identifies the advertising router i.e., the
prefix is a host prefix advertising a globally reachable address
typically associated with a loopback address.
The advertising router MAY choose to NOT set this flag even when
the above conditions are met.
If the flag is set and the prefix length is NOT a host prefix
(/32 for IPV4, /128 for IPv6) then the flag MUST be ignored.
The flag is preserved when leaked between levels.
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2.2. IPv4/IPv6 Source Router ID
When a reachability advertisement is leaked from one level to
another, the source of the original advertisement is unknown. In
cases where the advertisement is an identifier for the advertising
router (e.g., N-flag set in the Extended Reachability Attribute sub-
TLV as described in the previous section) it may be useful for other
routers to know the source of the advertisement. The sub-TLVs
defined below provide this information.
IPv4 Source Router ID
Type: 11 (suggested - to be assigned by IANA)
Length: 4
Value: IPv4 Router ID of the source of the advertisement
Inclusion of this TLV is optional and MAY occur in TLVs
135, 235, 236, or 237.
If present the sub-TLV MUST be included when the prefix
advertisement is leaked to another level.
IPv6 Source Router ID
Type: 12 (suggested - to be assigned by IANA)
Length: 16
Value: IPv6 Router ID of the source of the advertisement
Inclusion of this TLV is optional and MAY occur in TLVs
135, 235, 236, or 237.
If present the sub-TLV MUST be included when the prefix
advertisement is leaked to another level.
3. IANA Considerations
This document adds the following new sub-TLVs to the registry of sub-
TLVs for TLVs 135, 235, 236, 237.
Value: 4 (suggested - to be assigned by IANA)
Name: Prefix Attribute Flags
Value: 11 (suggested - to be assigned by IANA)
Name: IPv4 Source Router ID
Value: 12 (suggested - to be assigned by IANA)
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Name: IPv6 Source Router ID
This document also introduces a new registry for bit values in the
Prefix Attribute Flags sub-TLV. Registration policy is Expert Review
as defined in [RFC5226]. Defined values are:
Bit # Name
----- ------------------------
0 External Prefix Flag
1 Re-advertisement Flag
2 Node Flag
4. Security Considerations
None.
5. Acknowledgements
TBD
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in Intermediate System to
Intermediate Systems (IS-ISs)", RFC 5120, February 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5308] Hopps, C., "Routing IPv6 with IS-IS", RFC 5308, October
2008.
6.2. Informational References
[SR] "IS-IS Extensions for Segment Routing, draft-ietf-isis-
segment-routing-extensions-03(work in progress)", October
2014.
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Authors' Addresses
Les Ginsberg
Cisco Systems
510 McCarthy Blvd.
Milpitas, CA 95035
USA
Email: ginsberg@cisco.com
Bruno Decraene
Orange
38 rue du General Leclerc
MIssy Moulineaux cedex 9 92794
France
Email: bruno.decraene@orange.com
Clarence Filsfils
Cisco Systems
Email: cfilsfils@cisco.com
Stephane Litkowski
Orange Business Service
Email: stephane.litkowski@orange.com
Stefano Previdi
Cisco Systems
Via Del Serafico 200
Rome 0144
Italy
Email: sprevidi@cisco.com
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