Subject: Re: My comment on draft-mirtorabi-ospf-tunnel-adjacency

From: "Pat Murphy - (650)329-4044" <[email-masked]>
Date: Fri, 14 Nov 2003 10:44:29 -0700

>The fact is that TA path cannot go over each other therefore after the
>first encapsulation the packet will be dropped.

What's confusing me is that I remember anything in your draft that
prevents this. Perhaps your new posting will be more illuminating.

>It has nothing to do with detecting the failure.

>If you still think that this is possible please provide metric with the
>shortest path taken with each TA in your example

So assume that the Xs failure is detected imediately by the SPF
algorithm of each Area, that the TAs have metric 100, the direct links
have metric 1, and that the TA RouterDead interval (or LSU failure)
keeps the TAs up for 10 seconds after the failure is detected.

Pat

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From: Sina Mirtorabi <[email-masked]>
Date: Fri, 14 Nov 2003 11:25:06 -0800

Pat,

->>The fact is that TA path cannot go over each other therefore
->after the
->>first encapsulation the packet will be dropped.

P->What's confusing me is that I remember anything in your draft
P->that prevents this. Perhaps your new posting will be more
P->illuminating.

In a normal scenario, a simple match shows that two TA cannot go over
each other

- TA1 is going over a physical link with a cost of C1, so TA1 cost is C1
- TA2 is going over a physical link with a cost of C2, so TA2 cost is C2

TA1 can go over TA2 if C1 > C2  [i]  ( that is the direct cost is more )

Now once [i] is true TA2 cannot go any more over TA2 because for that we
should have C2 > C1 which is against [i]

->>It has nothing to do with detecting the failure.
->
->>If you still think that this is possible please provide
->metric with the
->>shortest path taken with each TA in your example

P->So assume that the Xs failure is detected imediately by the
P->SPF algorithm of each Area, that the TAs have metric 100, the
P->direct links have metric 1, and that the TA RouterDead
P->interval (or LSU failure) keeps the TAs up for 10 seconds
P->after the failure is detected.

In a failure scenario where you detect quickly that your link is down
and the only remaining path or shortest path is the other TA, for the
duration that the TA is brought down you could use the other TA

As I have stated before this is only during a transition time that TA
are brought down. I believe if there are real concerns for that we can
do what Acee suggested, i.e never use a TA in the SPT of another TA

Thanks
Sina