Re: [Idr] draft-uttaro-idr-bgp-persistence-00

Robert,

Comments In-Line

Thanks,
	Jim Uttaro

-----Original Message-----
From: idr-bounces@ietf.org [mailto:idr-bounces@ietf.org] On Behalf Of Robert Raszuk
Sent: Friday, October 21, 2011 6:24 PM
To: idr@ietf.org List
Subject: [Idr] draft-uttaro-idr-bgp-persistence-00

Hi,

I have read the draft and have one question and one observation.

Question:

What is the point of defining DO_NOT_PERSIST community ? In other words 
why not having PERSIST community set would not mean the same as having 
path marked with DO_NOT_PERSIST.

Observation:

I found the below statement in section 4.2:

    o  Forwarding must ensure that the Next Hop to a "stale" route is
       viable.

Of course I agree. But since we stating obvious in the forwarding 
section I think it would be good to explicitly also state this in the 
best path selection that next hop to STALE best path must be valid.

However sessions especially those between loopbacks do not go down for 
no reason. Most likely there is network problem which may have caused 
those sessions to go down. It is therefor likely that LDP session went 
also down between any of the LSRs in the data path and that in spite of 
having the paths in BGP and next hops in IGP the LSP required for both 
quoted L2/L3VPN applications is broken. That may particularly happen 
when network chooses to use independent control mode for label allocation.
[Jim U>] Why do you believe that? BGP can and does fail independently of the underlying LDP session.. I do believe that viability of a data path between two endpoints should be taken into account when validating paths to NHs but that effort is clearly a much bigger effort.. This draft would take advantage of this mechanism but I am not looking to define that in this draft..

I would suggest to at least add the recommendation statement to the 
document that during best path selection especially for stale paths a 
validity of required forwarding paradigm to next hop of stale paths 
should be verified.
[Jim U>] Why would this not be something that needs to be done as a general rule for paths.. I mean the underlying LSP could fail independently of BGP.. If this needs to be done in should be done as a general rule...

For example using techniques as described in: 
draft-ietf-idr-bgp-bestpath-selection-criteria

Best regards,
R.

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