Subject: Ordered FIB approach & broadcast links

From: Alia Atlas <[email-masked]>
Date: Tue, 12 Apr 2005 11:34:39 -0400

In the design team discussion, a question with the Ordered FIBs approach to 
micro-loop prevention was whether it could handle both "positive" and 
"negative" news in the same set of topology changes.  In general, this was 
seen as a nice to have.

I believe that the broadcast link case may make this necessary.  The 
scenario I am thinking of is where the interface from the DR on a broadcast 
link fails.  As a result, the backup DR will start announcing the router 
LSA needed for the pseudo-node.  This will look like a pseudo-node has 
failed & as if a new pseudo-node has appeared with all of its links.

What do others think?

I know that the DT decided on PLSN for the basic approach - but there's the 
possibility that a different advanced method might become desirable.

Alia

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From: mike shand <[email-masked]>
Date: Wed, 13 Apr 2005 09:33:53 +0100

At 11:34 12/04/2005 -0400, Alia Atlas wrote:
>In the design team discussion, a question with the Ordered FIBs approach 
>to micro-loop prevention was whether it could handle both "positive" and 
>scenario I am thinking of is where the interface from the DR on a 
>broadcast link fails.  As a result, the backup DR will start announcing 
>the router LSA needed for the pseudo-node.  This will look like a 
>pseudo-node has failed & as if a new pseudo-node has appeared with all of 
>its links.

Alia,

Yes, good point. That is certainly true, and looks like it could get rather 
messy:-(

I'm wondering whether it might be possible to deal with this at a higher 
level. i.e. rather than consider the pseudonode represented topology which 
has been severely shaken about by the DR changeover, is there some way we 
can consider the "real" topology which has simply lost a node. This might 
involve some special case processing of pseudonodes, but it might avoid the 
other complication.

Haven't had a chance to think seriously about this. I just throw it out as 
a possibility for further thought.

         Mike

>What do others think?
>
>I know that the DT decided on PLSN for the basic approach - but there's 
>the possibility that a different advanced method might become desirable.
>
>Alia
>
>

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From: mike shand <[email-masked]>
Date: Wed, 13 Apr 2005 11:19:11 +0100

Alia,
         Thinking about this just a tiny bit more, when we have a failure 
of a DR, if we compare the old topology and the new topology, apart from 
the actual node itself going away, the only difference is that the NAME of 
the pseudonode has changed. All the links and costs to it and from it must 
be the same as they were before (except for the links to and from the 
physically failed node of course).

         So if there were some way we could recognize this, we could just 
ignore the problem.

         Mike

At 09:33 13/04/2005 +0100, mike shand wrote:
>>"negative" news in the same set of topology changes.  In general, this 
>>was seen as a nice to have.
>>
>Yes, good point. That is certainly true, and looks like it could get 
>rather messy:-(
>
>involve some special case processing of pseudonodes, but it might avoid 
>the other complication.
>

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From: Alia Atlas <[email-masked]>
Date: Wed, 13 Apr 2005 10:24:10 -0400

Mike,

I agree that recognizing the pseudo-node has changed its name would remove 
this additional concern for handling "good news" and "bad news" 
simultaneously.

Alia

At 06:19 AM 4/13/2005, mike shand wrote:
> the actual node itself going away, the only difference is that the NAME 
> of the pseudonode has changed. All the links and costs to it and from it 
> must be the same as they were before (except for the links to and from 
> the physically failed node of course).
>
>>>pseudo-node has failed & as if a new pseudo-node has appeared with all 
>>>of its links.
>>
>>Alia,
>>
>>level. i.e. rather than consider the pseudonode represented topology 
>>which has been severely shaken about by the DR changeover, is there some 
>>way we can consider the "real" topology which has simply lost a node. 
>>This might involve some special case processing of pseudonodes, but it 
>>might avoid the other complication.
>>
>>Haven't had a chance to think seriously about this. I just throw it out 
>>as a possibility for further thought.
>>
>>         Mike
>>
>>
>>
>>>What do others think?
>>>