Subject: question about fast-reroute

From: "Doug Degan" <[email-masked]>
Date: Thu, 7 Mar 2002 17:55:26 +0200

0) what is wrong in this story?
   --------------------------------------

consider the folowing topology:

[I]---[PLR]----[T1]-----[MP]-----[T2]----[E]
        \                    /
         \------------------/
            BYPASS/DETOUR

primary LSP is from I to E,  it is protected at PLR by BYPASS/DETOUR lsp.
(this wasn't configured manually, but was done upon configuring the protected LSP)

now the link between T2 and E fails.
T2 send PATH-ERR upstream cause it can't protect the primary LSP.
same goes to MP and T1 (sending PATH-ERR upstream).
PLR get the PATH_ERR and switch the traffic to the BYPASS/DETOUR.

if what I have describes may happen I have other questions except the "0" question:
1) should PLR know per each possible failure position whether it is protected against it? (how...)

2) should PLR always select the "farest-merge" bypass? (in this case it might have prevented traffic loss).

thanks in forward.
doug.

---

From: Sachin Kalra <[email-masked]>
Date: Thu, 07 Mar 2002 11:22:55 -0500

Doug:

If link between [T2] and [E] fails, then [PLR] should not switch the 
traffic to Bypass Tunnel.

I agree that PLR should NOT know for each possible failure position whether 
it is protected against it.

Whereas, it should know the positions that it protects. Thus in this case, 
PLR should know that it protects
a. Link [PLR]--[T1]
b. node [T1]
c. Link [T1]--[MP]

So, whenever PLR receives a PATH-ERR, it will know if protection can be done.

Regards,
Sachin Kalra

>0) what is wrong in this story?

===========================================================
Sachin Kalra
Modeling Engineer
OPNET Technologies, Inc.
(240)-497-3000 x2796
===========================================================

---

From: "Doug Degan" <[email-masked]>
Date: Thu, 7 Mar 2002 19:54:16 +0200

In that case it should also be updated in the draft.
I didn't find the place where it says something like - 
on failure detection at X PLR checks if the LSP is localy protected against failures in X and only then switches transportation to the bypass/detour.

  ----- Original Message ----- 
  From: Sachin Kalra 
  To: Doug Degan ; [email-masked] 
  Sent: Thursday, March 07, 2002 6:22 PM
  Subject: Re: question about fast-reroute

  Doug:

  If link between [T2] and [E] fails, then [PLR] should not switch the traffic to Bypass Tunnel.

  I agree that PLR should NOT know for each possible failure position whether it is protected against it.

  Whereas, it should know the positions that it protects. Thus in this case, PLR should know that it protects
  a. Link [PLR]--[T1]
  b. node [T1]
  c. Link [T1]--[MP]

  Regards,
  Sachin Kalra

     

     

     

     
    thanks in forward.
    doug.

---

From: Alia Atlas <[email-masked]>
Date: Thu, 07 Mar 2002 13:04:44 -0600

In the case described below, the PathErr sent by T2 would be duplicated
by MP and sent up both the primary LSP and the detour.

If there was a bypass tunnel with an unsignaled backup instead, then what
would happen is that PLR would try to fail over to a backup through the
byass tunnel.  PLR would send a Path message for the backup through
the bypass tunnel; MP, upon receiving that message, would return a
PathErr.  Once PLR receives the PathErr on its backup and on its
primary, then PLR will send the PathErr upstream.

Practically, such a scenario only happens when a primary LSP is not fully
protected at each hop.

Alia

At 07:54 PM 3/7/02 +0200, Doug Degan wrote:

In that case it should also be updated in the
draft.

on failure detection at X PLR checks if the LSP is localy protected
against failures in X and only then switches transportation to the
bypass/detour.

----- Original Message -----

From: Sachin Kalra

To: Doug Degan ;
[email-masked]

Doug:

I agree that PLR should NOT know for each possible failure position
whether it is protected against it.

Whereas, it should know the positions that it protects. Thus in this
case, PLR should know that it protects

a. Link [PLR]--[T1]

b. node [T1]

c. Link [T1]--[MP]

So, whenever PLR receives a PATH-ERR, it will know if protection can be
done.

Regards,

Sachin Kalra

0) what is wrong in
this story?

\
/

\------------------/

BYPASS/DETOUR

primary LSP is from I to E,  it is
protected at PLR by BYPASS/DETOUR lsp.

(this wasn't configured manually, but was done upon configuring the
protected LSP)

now the link between T2 and E
fails.

if what I have describes may happen I have
other questions except the "0" question:

1) should PLR know per each possible failure position whether it is
protected against it? (how...)

2) should PLR always select the
"farest-merge" bypass? (in this case it might have prevented
traffic loss).

thanks in forward.

doug.

Sachin Kalra

Modeling Engineer

OPNET Technologies, Inc.

(240)-497-3000 x2796

---

From: Jean Philippe Vasseur <[email-masked]>
Date: Fri, 08 Mar 2002 18:30:35 +0100

Doug,

- Receiving a PERR any PLR can detect whether the TE LSP has been fast 
protected downstream (in this case, the PERR specifies "Tunnel Locally 
repaired)
- Receiving a PERR indicating a fialure downstream, if the TE LSP is not 
being protected, an upstream PLR could decide to trigger a fast reroute 
provided the bypass tunnel is terminating downstream the failure (for a 
DETOUR LSP it terminates at the tail-end).

JP.