draft-ietf-idr-bgp-dpa-04.txt   draft-ietf-idr-bgp-dpa-05.txt 
INTERNET-DRAFT Enke Chen INTERNET-DRAFT Enke Chen
<draft-ietf-idr-bgp-dpa-04.txt> Tony Bates <draft-ietf-idr-bgp-dpa-05.txt> Tony Bates
Expires in six months MCI Expires September 1996 MCI
January 1996 March 1996
Destination Preference Attribute for BGP Destination Preference Attribute for BGP
<draft-ietf-idr-bgp-dpa-04.txt> <draft-ietf-idr-bgp-dpa-05.txt>
Status of this Memo Status of this Memo
This document is an Internet Draft. Internet Drafts are working This document is an Internet Draft. Internet Drafts are working
documents of the Internet Engineering Task Force (IETF), its Areas, documents of the Internet Engineering Task Force (IETF), its Areas,
and its Working Groups. Note that other groups may also distribute and its Working Groups. Note that other groups may also distribute
working documents as Internet Drafts. working documents as Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by months. Internet Drafts may be updated, replaced, or obsoleted by
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This document proposes the DPA path attribute, which is an optional This document proposes the DPA path attribute, which is an optional
transitive attribute of fixed length. The attribute is represented transitive attribute of fixed length. The attribute is represented
by a pair <AS#, DPA value>. The AS# is a two octet non-negative by a pair <AS#, DPA value>. The AS# is a two octet non-negative
integer, which denotes the AS that specifies the preference. The DPA integer, which denotes the AS that specifies the preference. The DPA
value is a four octet non-negative integer. value is a four octet non-negative integer.
The DPA attribute has Type Code 11. The DPA attribute has Type Code 11.
Route Selection Process Route Selection Process
The DPA attributes shall be used as a route selection criteria, after A router may use DPA to influence the degree of preference [1]
the "LOCAL_PREF" attribute is evaluated, and before the evaluation of assigned to a route.
the AS path length and the multi-exit-discriminator (MED) attribute.
However, if a route contains both MED and DPA attributes from the
same neighboring AS, the MED values shall be favored over DPA values
for route selection.
The higher the DPA attribute value, the more preferred the route.
A route with missing DPA attribute must be treated as having an DPA DPA influence on the computation of degree of preference is a local
attribute with value zero. matter. In general, a route with a higher DPA indicates a higher
preference by the originator of the DPA attribute.
Operation Operation
The AS that sets this attribute must include its AS number in the The AS that sets this attribute must include its AS number in the
attribute. A BGP speaker may use the "LOCAL_PREF" attribute to attribute. A BGP speaker may use the "LOCAL_PREF" attribute to
select a different path other than the one specified by the DPA select a different path other than the one specified by the DPA
attribute value. This does not preclude an AS from re-setting this attribute value. This does not preclude an AS from re-setting this
attribute. However, coordination with the upstream and/or downstream attribute. However, coordination with the upstream and/or downstream
neighbors is strongly recommended. neighbors is strongly recommended.
To make sure that the MED attribute and not the DPA attribute is used
in the selection of routes from multiple peers of the same
neighboring AS, the DPA value, if set, must be identical for all
peers with the same neighboring AS. It is an operational matter to
ensure the correct setting of the DPA value for multiple peers to the
same neighboring AS.
Aggregation Aggregation
If aggregation is done, the resultant aggregate shall be treated as a If aggregation is done, the resultant aggregate shall be treated as a
new NLRI. No DPA attribute shall be derived from more specific NLRIs new NLRI. No DPA attribute shall be derived from more specific NLRIs
which formed the aggregate. The resultant aggregate is free to have which formed the aggregate. The resultant aggregate is free to have
the DPA attribute set if so desired. the DPA attribute set if so desired.
Remarks Remarks
It is noted that this new BGP attribute is simple and requires little It is noted that this new BGP attribute is simple and requires little
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subsequent versions of BGP unless specifically noted otherwise. subsequent versions of BGP unless specifically noted otherwise.
Security Considerations Security Considerations
Security considerations are not discussed in this memo. Security considerations are not discussed in this memo.
Acknowledgments Acknowledgments
The authors would like to thank Yakov Rekhter of cisco for his The authors would like to thank Yakov Rekhter of cisco for his
insightful comments and suggestions. We also acknowledge Ramesh insightful comments and suggestions. We also acknowledge Ramesh
Govindan (ISI) and Ravi Chandra (cisco) for their helpful comments. Govindan (ISI), Paul Traina (cisco), and Ravi Chandra (cisco) for
their helpful comments.
References References
[1] Rekhter, Y., and Li, T., "A Border Gateway Protocol 4 (BGP-4)", [1] Rekhter, Y., and Li, T., "A Border Gateway Protocol 4 (BGP-4)",
RFC1771, March 1995. RFC1771, March 1995.
[2] Y. Rekhter, and P. Gross, "Application of the Border Gateway [2] Y. Rekhter, and P. Gross, "Application of the Border Gateway
Protocol in the Internet", RFC1772, March 1995. Protocol in the Internet", RFC1772, March 1995.
[3] Chen, E., and Bates, T., "Current Practice of Implementing [3] Chen, E., and Bates, T., "Current Practice of Implementing
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