The MPLS-OPS Archive

[Muhammad Tahir <muhammadtahir2000@yahoo.com>]

Nisar:

Yes, it is clear that request is from the ingress to egress, and label distribution is
from egress to ingress (as a result creats LSP).

As you have indicated the "refresh messages", yes its true in case of RSVP but what about
LDP/CR-LDP? What I remember is, in case of LDP/CR-LDP, it needs no refresh. Once it is up
it stays up until torn down, i.e. LSP continues indefinitely until "some failure" occurs.

Actually I want more "specific" knowledge related to this issue and this is what I have
asked in the questions. 
Please correct my "possible answers" for each question. Please confirm them by YES or NO
and if possible an explanation or hint for further reading.

Your kind help will be highly appreciated!

Thanks again
Tahir




--- Nisar Ali <nisar@juniper.net> wrote:

> Tahir:
> 
> LSP are setup based on a request from the ingress node; but the
> label assignments start from egress back to ingress. 
> 
> There are some refresh intervals associated with each LSP. Every
> interval some refresh messages (path messages for example) are 
> exchanged. If these messages get lost; we wait for a timer
> to expire and continue to send those refresh messages. If we
> do not receive those messages in that interval; the LSP is 
> torn down and its state is removed. 
> 
> Now the reason for those refresh messages getting lost; could
> be anything from a link failure to a node failure or some other
> routing issue.
> 
> I am not sure if I have answered your questions to exactly
> what you were asking. But let me know... if I can be of any
> more help.
> 
> Thanks.
>  nisar
> 
> On Thu, Feb 10, 2005 at 05:13:58AM -0800, Muhammad Tahir wrote:
> > Hi all,
> > 
> > Please tell me if i am wrong in answering these questions/also please indicate from
> where
> > can i read more about each question(drafts/rfc/book/articles etc).
> > 
> > 1- LSP session remains for how much time or in other words upto what time LSP
> persists?
> > (possible answer): LSP between source and destination finishes, when packets of a
> certain
> > application (or FECs) reached at the destination. Other possiblity is, it continues
> until
> > some network failure occurs. 
> > 
> > 2- If the source is delivering the last packets of one FEC (or application)to
> destination
> > and it receives some packets belonging to a new FEC or a new application for the SAME
> > destination. 
> > (possible answer): It will NOT terminate the first LSP and will continue for the new
> > packets by using the same LSP. 
> > 
> > 3- When LSP is terminated? 
> > (possible answer): It is terminated when there is request from upstream or
> downstream.
> > (usual termination) or It may terminate when there is link failure or device problem
> etc.
> > (unusual termination). 
> > 
> > 4- Is it terminated BY upstream or downstream in case of usual termination?
> > (possible answer): Both can request for LSP termination. 
> > 
> > 5- How, in case of usual LSP termination, upstream or downstream requests for LSP
> > termination? (procedure?)
> > (possible answer): They use the LDP or RSVP procedures for this task. 
> > 
> > 6- How LSRs come know that there is no more LSP in unusual termination?
> > (possible answer): They will come to know by the information provided by IGP. 
> > 
> > 7- What the routers will do in case of LSP usual and unusual termination?
> > (possible answer): They will withdraw the labels. 
> > 
> > 8- How usual LSP termination takes place? By label distribution protocols e.g. LDP or
> > LSVP etc. 
> > (possible answer): In case of LDP and RSVP, LSP will continue until node failure or
> link
> > failure occurs. 
> > 
> > Thanks
> > 
> > Tahir
> > 
> > 
> > 		
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> -- 
> ================================================
> Nisar Ali
> Network Engineering Team (NET)
> ===============================================
> 



		
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