< draft-ietf-isis-ipv6-06.txt   draft-ietf-isis-ipv6-07.txt >
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Draft Author(s): Status of this Memo
Chris Hopps <chopps@rawdofmt.org>
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This draft specifies a method for exchanging IPv6 routing information
using the IS-IS routing protocol. The described method utilizes 2
new TLVs, a reachability TLV and an interface address TLV to
distribute the necessary IPv6 information throughout a routing
domain. Using this method one can route IPv6 along with IPv4 and OSI
using a single intra-domain routing protocol.
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].
1. Overview
IS-IS is an extendible intra-domain routing protocol. Each router in
the routing domain issues an LSP that contains information pertaining
to that router. The LSP contains typed variable length data often
referred to as TLVs (type-length-values). We extend the protocol
with 2 new TLVs to carry information required to perform IPv6
routing.
In [RFC1195] a method is described to route both OSI and IPv4. We
utilize this same method with some minor changes to allow for IPv6.
To do so we must define 2 new TLVs, namely "IPv6 Reachability" and
"IPv6 Interface Address" and a new IPv6 protocol identifier. In our
new TLVs we utilize the extended metrics and up/down semantics of
[RFC2784].
2. IPv6 Reachability TLV
The "IPv6 Reachability" TLV is TLV type 236 (0xEC).
[RFC1195] defines 2 Reachability TLVs, "IP Internal Reachability
Information" and "IP External Reachability Information". We provide
the equivalent IPv6 data with the "IPv6 Reachability" TLV and an
"external" bit.
The "IPv6 Reachability" TLV describes network reachability through
the specification of a routing prefix, metric information, a bit to
indicate if the prefix is being advertised down from a higher level,
a bit to indicate if the prefix is being distributed from another
routing protocol and OPTIONALLY the existence of Sub-TLVs to allow
for later extension. This data is represented by the following
structure:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 236 | Length | Metric .. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .. Metric |U|X|S| Reserve | Prefix Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Sub-TLV Len(*) | Sub-TLVs(*) ...
* - if present
U - up/down bit
X - external original bit
S - subtlv present bit
The above IPv6 Reachability TLV MAY appear any number of times
(including none) within an LSP. Link-local prefixes MUST NOT be
advertised using this TLV.
As is described in [RFC2784], "the up/down bit is set to 0 when a
prefix is first injected into IS-IS. If a prefix is redistributed
from a higher level to a lower level (e.g., level two to level one),
the bit SHALL be set to 1 to indicate that the prefix has travelled
down the hierarchy. If a prefix is redistributed from an area to
another area at the same level then the up/down bit SHALL be set to
1."
If the prefix was distributed into IS-IS from another routing
protocol the external bit SHALL be set to 1. This information is
useful when distributing prefixes from IS-IS to other protocols.
If the Sub-TLV bit is set to 0 then the octets of Sub-TLVs are not
present. Otherwise the bit is 1 and the octet following the prefix
will contain the length of the Sub-TLV portion of the structure.
The prefix is "packed" in the data structure. That is, only the
required number of octets of prefix are present. This number can be
computed from the prefix length octet as follows:
prefix octets = integer of ((prefix length + 7) / 8)
Just as in [RFC2784], if a prefix is advertised with a metric larger
than MAX_V6_PATH_METRIC (0xFE000000), this prefix MUST not be
considered during the normal SPF computation. This will allow
advertisement of a prefix for purposes other than building the normal
IPv6 routing table.
If Sub-TLVs are present they have the same form as normal TLVs as
shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value(*) ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* - if present
Length indicates how many octets of value are present and can be 0.
3. IPv6 Interface Address TLV
The "IPv6 Interface Address" TLV is TLV type 232 (0xE8).
TLV 232 maps directly to "IP Interface Address" TLV in [RFC1195] .
We necessarily modify the contents to be 0-15 16 octet IPv6 interface
addresses instead of 0-63 4 octet IPv4 interface address.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 232 | Length | Interface Address 1(*) .. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .. Interface Address 1(*) .. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .. Interface Address 1(*) .. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .. Interface Address 1(*) .. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Interface Address 1(*) .. | Interface Address 2(*) ..
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* - if present
We further restrict the semantics of this TLV depending on where it
is advertised. For Hello PDUs the "Interfaces Address" TLV MUST
contain only the link-local IPv6 addresses assigned to the interface
which is sending the Hello. For LSPs the "Interfaces Address" TLVs
MUST contain only the non-link-local IPv6 addresses assigned to the
IS.
4. IPv6 NLPID
The value of the IPv6 NLPID is 142 (0x8E).
As with [RFC1195] and IPv4, if the IS supports IPv6 routing using
IS-IS, it MUST advertise this in the "NLPID" TLV by adding the IPv6
NLPID.
5. Operation
We utilize the same changes to [RFC1195] as made in [RFC2784] for the
processing of prefix information. These changes are both related to
the SPF calculation.
Since the metric space has been extended we need to redefine the
MAX_PATH_METRIC (1023) from the original specification in [RFC1195].
This new value MAX_V6_PATH_METRIC is the same as in [RFC2784]
(0xFE000000). If during the SPF a path metric would exceed
MAX_V6_PATH_METRIC it SHALL be considered to be MAX_V6_PATH_METRIC.
The order of preference between paths for a given prefix MUST be
modified to consider the up/down bit. The new order of preference is
as follows (from best to worst).
1. Level 1 up prefix
2. Level 2 up prefix
3. Level 2 down prefix
4. Level 2 down prefix
If multiple paths have the same best preference then selection occurs
based on metric. Any remaining multiple paths SHOULD be considered
for equal-cost multi-path routing if the router supports this,
otherwise the router can select any one of the multiple paths.
6. IANA Considerations
IANA is requested to update the IS-IS codepoint registry
(http://www.iana.org/assignments/isis-tlv-codepoints) so that TLV
codes 232 and 236 refer to this document's RFC number.
IANA is additionally requested to create the following new code-point
registry for Sub-TLVs of TLV 236. The range of values for Type is
0-255. Allocations within the registry require documentation of the
use and approval by the Designated Expert assigned by the IESG
[RFC2434]. All code-points are currently unassigned.
Note to RFC Editor: this section may be removed on publication as an
RFC.
7. Security Considerations
This document raises no new security considerations. Security
considerations for the IS-IS protocol are covered in [ISO10589] and
in [RFC3567].
8. References
8.1. Normative References
[ISO10589]
"Intermediate System to Intermediate System Intra-Domain
Routeing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network
Service (ISO 8473)", 1992.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, December 1990.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3567] Li, T. and R. Atkinson, "Intermediate System to
Intermediate System (IS-IS) Cryptographic Authentication",
RFC 3567, July 2003.
8.2. Informative References
[RFC3787] Parker, J., "Recommendations for Interoperable IP Networks
using Intermediate System to Intermediate System (IS-IS)",
RFC 3787, May 2004.
Author's Address
Christian E. Hopps
Cisco Systems
170 W. Tasman Dr.
San Jose, California 95134
USA
Email: chopps@cisco.com
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