Re: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document

"Pradosh Mohapatra (pmohapat)" <pmohapat@cisco.com> Tue, 25 November 2008 15:58 UTC

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Thread-Topic: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document
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From: "Pradosh Mohapatra (pmohapat)" <pmohapat@cisco.com>
To: "Danny McPherson" <danny@tcb.net>, "Yakov Rekhter" <yakov@juniper.net>
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Subject: Re: [Idr] draft-walton-bgp-add-paths-06.txt as IDR WG document
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| ---
| While Path Identifier assignment is purely a local matter, 
| for operational reasons I believe that a receiving BGP 
| speaker SHOULD (MUST?) preserve any Path Identifier for an 
| associated path on receipt.  This will aid in operational debugging.

Right. It MUST preserve the path-id that it received in the path
structure since the id would be used for replacing any new 
advertisement received for that path or removing the path upon 
withdrawl.

| ---
| I wonder if it's necessary to state handling procedures in 
| S.6 of receipt of an update message that does not use 
| extended NLRI encoding from a peer that advertised they 
| support receive processing of the capability?  For example, 
| if an implementation wanted to optimize in some manner where 
| if only one path exists then don't use the the extended NLRI 
| encoding, because you could never pack updates, etc..
| 
| Perhaps receipt of an update for a prefix that does not use 
| extended ecoding from a peer that advertised the capability 
| should be handled normally, and not considered or generate an 
| error condition?

This makes parsing extremely difficult. Reception of the capability
from a peer is the only indication that the UPDATE parsing needs
to retrieve the first four octets as path-id and the prefix
follows after that. How would you differentiate an UPDATE message
where prefixes are encoded with path-id vs. another where they
aren't?

If a speaker is able to send only one path and has advertised
add-path capability, there are simpler ways to encode a (dummy)
path-id, like always encode 0 or 1 or whatever...

- Pradosh
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