Subject: RE:

From: Pedro Roque Marques <[email-masked]>
Date: Thu, 6 Jun 2002 13:45:40 -0700 (PDT)

Abarbanel, Benjamin writes:

>>> What is being dampened is not the route but whether we use the MED
>>> for this route in the BRSC calculations when we detect a route has
>>> been oscillating. Once, the route exits its oscillation state MED
>>> is automatically reapplied.
>>>
>>> General IBGP dampening can be done as was done in EBGP but for the problem
>>> we have been exposed to, the MED dampening should suffice.
>>>
>>> Yes, we would need to keep track of the routes previous history in
>>> order to know that it has entered oscillation state. This
>>> mechanism can be described in detail in a draft.
>>>

While i would encorage you to describe the proposal in detail, your
brief synopsis gives me the impression that you propose to ignore
certain attributes on different members of the ibgp mesh.

ibgp route decision mush be consistent enought to ensure that loops
are not formed. I don't think you can gurantee that if different
members of the mesh use different attributes.

  Pedro.

---

From: "Abarbanel, Benjamin" <[email-masked]>
Date: Thu, 6 Jun 2002 15:51:20 -0400

Pedro:

-----Original Message-----
From: Pedro Roque Marques [mailto:[email-masked]]
Sent: Thursday, June 06, 2002 3:35 PM
To: Abarbanel, Benjamin
Cc: [email-masked]
Subject: RE: 

Abarbanel, Benjamin writes:

> I have a third solution to propose to the list. Why not dampen the
> MED from the BGP Route Selection Criteria during conditions when a
> route is oscillating

As i mentioned in my previous e-mail to the list, the devil is in the
details...
Someone needs to specify the behaviour and do an analysis to see if it
is feasible... without some detailed analysis i don't think it is
possible to know if that is a feasible solution.

Keep in mind the following scenario:

You have N peering points with AS 1 in your ibgp mesh. Each of those N
points receives a route with an MED. When the best external route
changes, all of those N peering points advertise their external route
to the mesh and then withraw it as they converge to the second best
MED.

In this case are you going to hold dampening history for all these
paths ? Are you going to apply penalties to individual paths (as in
the ebgp case) or routes... don't forget that you need to dampen
things in a coverged state (i.e. no routing loops in the mesh).

>> for this route in the BRSC calculations when we detect a route has been 
>> oscillating. Once, the route exits its oscillation state MED is
automatically 
>> reapplied.  
>> Yes, we would need to keep track of the routes previous history in order
>> to know that it has entered oscillation state. This mechanism can be
>> described in detail in a draft.
>>
>> Ben