Network Working Group Ruchi Kapoor
Internet Draft Gargi Nalawade
Expires: December 2003 Chandra Appanna
Cisco Systems
BGPv4 SAFI-Specific Attribute
draft-kapoor-nalawade-idr-bgp-ssa-00.txt
1. Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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2. Abstract
This document defines a new BGP attribute called the "SAFI
[IANA-SAFI] Specific Attribute" (SSA). This attribute consists
of a set of TLVs (it MUST contain atleast one TLV; it MAY contain
more than one TLV). Each Subsequent Address Family Identifier
(SAFI) that uses this attribute MUST define the Typecodes that
are valid for the respective SAFI.
3. Introduction
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This document defines a new BGP attribute called the "SAFI
Specific Attribute" (SSA). The value part of the SSA consists
of a set of TLVs (it MUST contain atleast one TLV; it MAY contain
more than one TLVs). The intent behind SSA is to introduce an
attribute, which is flexible enough so that it has utility for
multiple applications.
The SSA provides a general way of encoding application (AFI/SAFI)
specific data. AFI/SAFIs may encode data in the form of TLVs. The
AFI/SAFI specific data does not necessarily have global meaning
across all AFI/SAFIs, i.e. some typecodes of the TLVs could be
relevant to only one AFI/SAFI. Each AFI/SAFI MUST specify the
Typecodes that are valid for the respective AFI/SAFI.
The SSA TLV is a variable length entity.
4. Format of the SAFI-Specific Attribute
The format of the BGP SSA attribute will be as follows:
| Attr. Flags | Attr.Type Code|
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|1|1|0|?|UNUSED | Type = TBD | Length (2 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Attribute Value |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The BGP SSA is a variable length, optional transitive attribute. The
Value field of the attribute may contain one or more SSA TLVs. The
Value field of the SSA Attribute is encoded as follows and may
contain one or more tuples of the following:
- Type Field : 2 octets
- Length Field: 2 octets
- Value Field : Variable
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
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type Field: The format of the Type Field is as shown below:
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
T - Transitive bit
Value 1: The SSA type is transitive across ASes
Value 0: The SSA type is non-transitive across ASes
Remaining 15 bits: Indicate the type of the SSA TLV.
Length Field: The Length is 2 octets long and indicates the length
of the Value field.
The value contained in this Length field MUST not exceed the total
length of the BGP SSA Attribute minus the total length of any prior
TLVs.
Value Field: The Value Field contains a TLV where the Types of the
TLV are defined by the respective SAFIs. The TLV in the Value field
of this Attribute will be of the form :
- Type Field : 2 octets
- Length Field: 2 octets
- Value Field : Variable
The Value field will have a fixed part as specified by the
respective SAFI-Specific Types and may have a variable part in the
form of Sub-TLVs encoded as follows :
- Sub-Type Field : 1 octets
- Length Field: 1 octets
- Value Field : Variable
5. Operation
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A BGP speaker that supports a SAFI, MUST accept any SSA TLVs that
are defined as valid for the SAFI. If the SSA TLV is transitive,
the BGP speaker MUST forward it even if it does not understand it.
Operation rules are governed by those for the SAFI. This attribute
only requires that it be forwarded even when it is not understood.
When sending an UPDATE message for this SAFI to a peer, a BGP speaker
MUST only advertise the SSA TLVs that are defined and are valid for
that SAFI.
A Capability has not been defined for this attribute intentionally.
For newer SAFIs, it is concieved that presence of the SAFI would
imply understanding the SSA attribute and the SSA TLVs. If existing
SAFIs make use of this Attribute, a capability may be defined
depending on the operational rules defined when the valid Typecodes
for this attribute are defined for that SAFI.
6. Security Considerations
This extension to BGP does not change the underlying security
issues.
7. Acknowledgements
We would like to thank Dan Tappan, Arjun Sreekantiah, Jim Guichard,
Shyam Suri and John Scudder for their comments and suggestions.
8. Normative References
[BGP-4] Rekhter, Y. and T. Li (editors), "A Border Gateway Protocol
4 (BGP-4)", Internet Draft draft-ietf-idr-bgp4-17.txt, January 2002.
[BGP-CAP] Chandra, R., Scudder, J., "Capabilities Advertisement with
BGP-4", draft-ietf-idr-rfc2842bis-02.txt, April 2002.
[IANA-AFI] http://www.iana.org/assignments/address-family-numbers.
[IANA-SAFI] http://www.iana.org/assignments/safi-namespace.
9. Authors' Addresses
Ruchi Kapoor
Cisco Systems, Inc
170 West Tasman Drive
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San Jose, CA 95134
Email:ruchi@cisco.com
Gargi Nalawade
Cisco Systems, Inc
170 West Tasman Drive
San Jose, CA 95134
Email:gargi@cisco.com
Chandra Appanna
Cisco Systems, Inc
170 West Tasman Drive
San Jose, CA 95134
Email: achandra@cisco.com
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12. Expiration Date
This memo is filed as <draft-kapoor-nalawade-idr-bgp-ssa-00.txt>, and
expires Dec, 2003.
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