Subject: Re:

From: Snigdho Bardalai <[email-masked]>
Date: Wed, 27 Feb 2002 11:04:20 -0800 (PST)

Hi,

Could you please help me understand how the NNHOP
Bypass tunnel works as described in Secion 6.5.

Consider the network below (from Section 1.2):

                [R8]
                    \
              [R1]---[R2]----[R3]----[R4]---[R5]
                         \\          //   \
                          [R6]===[R7]     [R9]

Say, labels available at R2 are L1 for the working
tunnel from R3 and L2 for the bypass tunnel from R6.

Again, labels available at R3 are L3 for the working
tunnel from R4.

Now when a packet is switched from the working tunnel
onto the bypass tunnel at R2 the label stack (as
described) will be L2->L1.

When the packet leaves R7 (the penultimate hop) the
label stack is L1.

At R4 it is expecting to L3, whereas it sees L1, won't
that be an error ?

Would appreciate a reply,
Thanks,
Snigdho

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From: Jean Philippe Vasseur <[email-masked]>
Date: Thu, 28 Feb 2002 12:03:53 +0100

Hi Snigdho,

>described) will be L2->L1.

No. In this case, the bypass tunnel is going to the NNHOP (R4 in the 
example above) so the PLR (R2) will redirect the traffic onto the BYPASS 
tunnel, replacing L1 by L3, pushing L2 and redirecting the traffic to R6 
(label stack = L2-L3). As described in section 6.1 of the draft, R2 learns 
the backup label to use (L3) from the RRO (prior to the failure). Then R7 
will perform a PHP and the MP (R4) will receive L3 as expected (but from a 
different interface). With a BYPASS tunnel going to the NHOP, the PLR would 
have acted as you described above. This applies to global label space at 
the Merge point.

JP.

---

From: Sachin Kalra <[email-masked]>
Date: Thu, 28 Feb 2002 11:19:41 -0500

Snigdho:

Please find my comments in-line.

>described) will be L2->L1.

<SK> No, this is incorrect. when switching a packet from working tunnel 
onto bypass tunnel at R2, the label stack will be L2->L3. So, R7 will pop 
up L2 and R4 will get L3. This is done using "Label recording" in the RRO 
"Record route object" when Primary LSP ("working tunnel": your terminology) 
is getting setup. Thus, R2 will know that R4 expects L3, so any Bypass 
terminating at R4 should have L3 as the top label.

>Would appreciate a reply,

Regards,
Sachin Kalra

---

From: Jean Philippe Vasseur <[email-masked]>
Date: Thu, 28 Feb 2002 19:36:50 +0100

At 11:19 28/02/2002 -0500, Sachin Kalra wrote:
>up L2 and R4 will get L3.

More precisely R7 will pop the top label which will not be L2 (as the top 
label would have been changed when received by R7) and R4 will receive L3 
as expected.

JP.

>This is done using "Label recording" in the RRO "Record route object" when 
>Primary LSP ("working tunnel": your terminology) is getting setup. Thus, 
>R2 will know that R4 expects L3, so any Bypass terminating at R4 should 
>have L3 as the top label.
>
>