The MPLS WG Archive

[Ping Pan <pingpan@cs.columbia.edu>]

Shahram Davari wrote:

>>What's been described in SAO is a user's desire. The routers 
>>may not be 
>>able to support it. For example, when a user asks for 
>>local-protection-desired and node-protection-desried, if a backup LSP 
>>cannot be established to skip the node, well, tough! ;-) Depending on 
>>the implementation, link protection may be used only instead.
>>
> 
> 
> Sure, but what I meant was, which one is desired by the user.
> Therefore I think it needs to be clarified.
> 


OK.


>>Path_Error messages are reference messages to the ingress. In other 
>>words, they are not that important. So a router can take its time to 
>>send the error messages. BTW, when a link/node goes down, it 
>>is possible 
>>that a router shoots out multiple error messages. One is to 
>>inform the 
>>ingress that the link/node is found to be dead. After the 
>>local repair, 
>>the node will tell the ingress "the LSP has been locally repaired".
>>
> 
> 
> My question was, does the PLR send the Error message periodically or only once?
> 


Hmmmm.... I see what you mean. The RSVP RFC didn't say how many error 
messages to be sent per error condition. In case of node/link failure, 
if the code was written in such a way to check the link/node status at 
every Path refresh cycle, an Path error may be generated every time. 
However, I don't think this is harmful. Of course you can coded it 
differently.


> 
> 
>>
>>>12) Section 9.2 permits having both types of protection 
>>>
>>(1-to-1 and facility) for the same PLR. 
>>
>>
>>>In that case how can it inform the ingress LSR that both
>>>protections are available?
>>>
>>>
>>
>>RRO tells the ingress that the traffic has been protected. Is 
>>it enough? 
>>  If not, there is a MIB draft on fast-reroute. ;-)
>>
> 
> I think it depends on which procedure is used to compute the
> Bypass tunnels. If the ingress computes the bypass tunnel, then
> it may need this info. And BTW, what is the relevance of MIB here?
> 


The ingress does not need to compute the bypass tunnel. Bypass tunnel 
computation could be a local decision.

http://www.ietf.org/internet-drafts/draft-ietf-mpls-fastreroute-mib-00.txt

- Ping