draft-ietf-idr-bgp-dpa-02.txt   draft-ietf-idr-bgp-dpa-03.txt 
INTERNET-DRAFT Enke Chen INTERNET-DRAFT Enke Chen
<draft-ietf-idr-bgp-dpa-02.txt> Tony Bates <draft-ietf-idr-bgp-dpa-03.txt> Tony Bates
MCI MCI
July 1995 November 1995
Destination Preference Attribute for BGP Destination Preference Attribute for BGP
<draft-ietf-idr-bgp-dpa-02.txt> <draft-ietf-idr-bgp-dpa-03.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
skipping to change at page 2, line 36 skipping to change at page 2, line 36
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 are considered comparable only if the DPA The DPA attributes are considered comparable only if the DPA
attributes are present in all the routes being compared and are set attributes are present in all the routes being compared and are set
by the same AS. by the same AS.
The comparable DPA attributes shall be used as a selection criteria, The comparable DPA attributes shall be used as a route selection
after the "local_pref" attribute is evaluated, and before the criteria, after the "local_pref" attribute is evaluated, and before
evaluation of the AS path length and the multi-exit-discriminator the evaluation of the AS path length and the multi-exit-discriminator
(MED). Non-comparable DPA attributes shall not be used in the route (MED) attribute. However, if a route contains both MED and comparable
DPA attributes from the same neighboring AS, the MED values shall be
favored over DPA values for route selection.
Non-comparable DPA attributes shall not be used in the route
selection process. selection process.
The higher the DPA attribute value, the more preferred the route. The higher the DPA attribute value, the more preferred the route.
Operation Operation
The DPA attribute should not be used as a replacement for MED. MED The AS that sets this attribute must include its AS number in the
should still be used when an AS has multiple connections to a single attribute. A BGP speaker may use the "local_pref" attribute to
neighboring AS. 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. However, coordination with the upstream and/or downstream
neighbors is strongly recommended.
The DPA attribute should only be set when needed. The AS that sets To make sure that the MED attribute and not the DPA attribute is used
this preference must include its AS number in the attribute. A BGP in the selection of routes from multiple peers of the same
speaker may use the "local_pref" attribute to prefer a different path neighboring AS, the DPA value, if set, must be identical for all
other than the one specified by the DPA attribute value. This does peers with the same neighboring AS. It is an operational matter to
not preclude an AS from re-setting this attribute. However, ensure the correct setting of the DPA value for multiple peers to the
coordination with the upstream and/or downstream neighbors is same neighboring AS.
strongly recommended.
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
skipping to change at page 3, line 44 skipping to change at page 4, line 7
The DPA path attribute may be used with BGP version 4 and all The DPA path attribute may be used with BGP version 4 and all
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. insightful comments and suggestions. We also acknowledge Ramesh
Govindan (ISI) 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
 End of changes. 

This html diff was produced by rfcdiff 1.23, available from http://www.levkowetz.com/ietf/tools/rfcdiff/