Subject: Questions about draft-swallow-rsvp-bypass-label-01

From: Sachin Kalra <[email-masked]>
Date: Tue, 13 Nov 2001 10:51:57 -0500

Hi All:

I have some questions about draft-swallow-rsvp-bypass-label-01.txt. Any 
help is greatly appreciated.

The draft states that (Pg 4, Line 11)
"...if R4 does not use a global label space then a label must be assigned 
out of the label space used by R4 on the interface terminating the link 
from R7. if, however, R4 has a global label space then the label which R2 
uses during the backup could be the same label value which is used by R3."

For the following topology
	[R8]
	      \
[R1]---------[R2]----[R3]----[R4]-----------------[R5]
	         \               //    \
                   [R6]===[R7]     [R9]

My questions are that if R4 does not use global label space (i.e. it has 
multiple label spaces, specific to particular interfaces) then

1> WHEN should the label be assigned out of label space used by R4 on the 
interface terminating the link from R7?
		a> Does it happens at the time when Primary LSP is signaled?
			If Yes, then how is [R2] informed about this label?

		b> Or does it happens at time when primary LSP fails and backup takeover?
			If Yes, then does this means that signaling for Backup LSP takes place?
	
		c> How does [R6] and [R7] decide in this case upon their labels to be 
used and when to swap and when to pop?

Please, if possible also send me some pointers to any drafts, RFCs or other 
readings related to this topic.
Thanks,
Sachin Kalra

---

From: Jean Philippe Vasseur <[email-masked]>
Date: Wed, 14 Nov 2001 23:41:26 +0100

Sachin,

>                         If Yes, then how is [R2] informed about this label?

a> is correct.

When per interface label space is used by the Merge Point, the PLR (R2) 
cannot learn the Backup Labels using the RRO object carried in the Resv 
message of the protected LSP. This is because the incoming labels learned 
via the RRO are interface-specific, and do not correspond to the interface 
on which the MP (R4) would receive a rerouted LSP's data packets.  When MPs 
use per interface label space, the PLR (R2) must send Path messages (for 
each Reroutable LSP) via the Backup Tunnel prior to the failure in order to 
discover the appropriate MP label.

JP.

>                 c> How does [R6] and [R7] decide in this case upon their 
> labels to be used and when to swap and when to pop?
>
>
>
>Please, if possible also send me some pointers to any drafts, RFCs or 
>other readings related to this topic.
>Thanks,
>Sachin Kalra