Re: Inter-Domain AS-Path failures

[Aleksi Suhonen <]

Bon soir,

Goetz Lichtwald wrote:
> > > > On Mon, Feb 28, 2005 at 03:09:31PM +0100, Goetz Lichtwald wrote:
> > > > > for research purpose I am looking for some facts concerning 
> > > > > inter-domain AS-path failures.

> > So you mean specifically BGP sessions timing out (session flaps)?
> > Or do you actually mean any session shutdown (for whatever reason)?

> I want know -- in real life -- how often BGP regards an AS-path to
> be broken, i.e. no KEEPALVIE messages can be exchanged -- at least 
> that is what BGP "thinks". This should result in an "BGP session timing
> out" (your first point). 

> From rom my understanding BGP tries to reestablish the BGP session for
> a certain time (ConnectRetry timer) and waits for an incoming BGP
> session request. So, concerning your second remark I am not quite
> sure if I got the point. Where is the difference between them? Is
> there a "meta-state" between a "session flap" and a "shut down"?

There are two states where the BGP session is down: Active and Idle.

Active means that the BGP speaker has started to connect the TCP
socket to its neighbour, but the connection isn't established yet.

Idle means that the BGP speaker is either sleeping for a while before
it retries. It can also mean that the BGP speaker has decided that
the TCP connection can't be formed at this time, due to there being
no valid route to the neighbour for example.

In addition to these two states, various vendors have added some
administrative shutdown states, such as Idle (Admin) and Idle (PfxCnt).
These are usually dead-end states that only a human operator can
clear.

> Anyway, for me it is important to get a feeling of how many of those
> session flaps occur with a duration on less than appr. 10 minutes.

In real life, BGP neighbour associations are TCP connections that have
an average lifetime measured in weeks or months.

--
	Aleksi Suhonen