Subject: RE:

From: Pedro Roque Marques <[email-masked]>
Date: Thu, 6 Jun 2002 14:28:51 -0700 (PDT)

Abarbanel, Benjamin writes:

my text:
> 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.

>>> This solution is no different than an operator going to a router
>>> with an oscillating route and deconfiguring the MED from it, while
>>> keeping the other routers unchanged.

When you 'unconfigure MED' from a route you basically strip that
attribute at the border router that receives it. Thus no
inconsistencies exist since everybody sees the same set of
attributes.

If done properly this manual condifuration never causes inconsistent
behaviour, since it affects what all routers see in terms of
attributes for the same path.

>>>
>>> BTW, when all the routers are equiped with the MED dampening, they
>>> will all reach the same conclusion with the state of the MED and they will
>>> all be consistent.
>>> 

Different members of an ibgp mesh see different routes and different
events... the number of flaps in a route is different. Most mesh
members have a different prespective and the potential to reach
different conclusions.

It is probably best for me to refrain from commenting further until i
see a concrete proposal which can then be analyzed. I just wanted to
caution you in advance to a set of issues that imho should be
addressed by such proposal.

  Pedro.

---

From: "Abarbanel, Benjamin" <[email-masked]>
Date: Thu, 6 Jun 2002 17:17:07 -0400

-----Original Message-----
From: Pedro Roque Marques [mailto:[email-masked]]
Sent: Thursday, June 06, 2002 4:46 PM
To: Abarbanel, Benjamin
Cc: [email-masked]
Subject: RE: 

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.

>> This solution is no different than an operator going to a router with
>> an oscillating route and deconfiguring the MED from it, while keeping
>> the other routers unchanged. Yes, inconsistancy will form, but
millisecond
>> route oscillation will be stoped much faster than an operator can first
>> find the router and second stop it by applying manual configuration
change.
>> Remember the router will have enough smarts to know the state of the
route 
>> and how to adjust its MED to dampen the oscillation. As others have said,
>> all solutions proposed will have temporary transient states that are not
>> healthy to the network.
>>
>> BTW, when all the routers are equiped with the MED dampening, they will
all
>> reach the same conclusion with the state of the MED and they will all be 
>> consistent.
>> 
>> Ben