Subject: Re: Label Stacking !!

From: "wu min" <[email-masked]>
Date: Mon, 08 Apr 2002 09:19:43 +0000

Hi,

Are you questioning how an LSR knows when to label stack? If that is your 
question IMHO, if the LSR in question awares that it is not directly linked 
to its peer, meaning that it is connected to the peer via a logical link 
that might have been established by means of traffic engineering where there 
exist one or more intermediate LSRs between the peer and itself, then it 
must perform label stacking. In this case, the LSR of interest must have 
engaged with its peer through LDP session found via extended discovery 
mechanism. All label exchanges within this session are associated with label 
stacking.

Although the LSR, at some point, views and treats the logical link as though 
it is one hop away link, but in actual fact it is a path.

Why two non-directly connected peers must perform label stacking is very 
obvious. The first level label (top label) is used to tunnel a packet 
through the logical link, the second level label is used by the receiving 
LSR at the other end of the tunnel for further label switching.

I may be wrong, but that is how I understand it. You may want to confirm 
this yourself. Please refer to RFC 3036 pg.10.

-Tze Ven.

>From: "Amarendra" <[email-masked]>
>To: <[email-masked]>
>Subject: Label Stacking !!
>Date: Thu, 4 Apr 2002 15:03:45 +0530
>
>Hi all,
>I am very much aware of Label Stack Encoding, but I have a few basic 
>related
>queries:
>1. How do we achieve label stacking using the Signalling protocols like 
>LDP,
>CR-LDP or RSVP-TE ?
>2. Do these protocols really play a role in Label Stacking ? I couldn't 
>find
>anything specifically related to this in these specs. Has the Extended
>Discovery mechanism of LDP anything to do with this ? I guess I am missing
>something here.
>Could anyone please provide pointers to this ?
>
>Regards,
>Amarendra.
>

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