From: Larry Metzger (larrymetzger@sbcglobal.net)
Date: Sun Jul 25 2004 - 02:02:31 GMT-3
For clarification....
The example that you are referring to is using NAT and the route to
null 0 is for the placement of a route to an address that otherwise does
not exist. I haven't taken my exam yet, but I will venture to guess
that this would be allowed if the situation was using NAT.
What would you say in this case???
Larry
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
James
Sent: Saturday, July 24, 2004 8:44 PM
To: Joseph D. Phillips
Cc: group study
Subject: Re: Using ip route to null 0 to advertise local network to BGP
peer
On Sat, Jul 24, 2004 at 08:12:37PM -0700, Joseph D. Phillips wrote:
> I notice in a couple places, Karl Solie and Leah Lynch, in CCIE
> Practical Studies II, use a static route to null 0 in order to make
sure
> that a local network advertises properly to a BGP peer.
What Karl and Leah had done is mostly done in real-world environment,
where it
is recommended that an AS always null-route w/ high A.D. their aggregate
to
prevent route-looping up to whomever they have default-route or less
specific
route pointed to (also to stabilize their BGP announcements when their
internal
IGP or connected interfaces holding the announced routes begin
flapping). This
seems like to be a BCP amongst most people doing BGP.
> For example, on page 805, there is an explicit advertisement of the
> 191.19.42.0/24 net within BGP, and just to be on the "safe" side, they
> added: ip route 191.19.42.0 255.255.255.0 null0 253
>
> I understand the need for a high administrative distance on the static
> route, but is this kind of route allowed in the lab exam?
Since it is statically/manually configured, IMHO it constitutes static
route.
So I think it is safer to stay away from doing that in lab unless you
are
permitted to do so.
>
> Is it one of those real world things we're not allowed to do on lab
day?
Sounds like it. :)
Since BGP scans rib before announcing a prefix, the only course of
action w/o
null route is probably to create loopbacks and assign addrs there..
-J
-- James Jun TowardEX Technologies, Inc. Technical Lead Network Design, Consulting, IT Outsourcing james@towardex.com Boston-based Colocation & Bandwidth Services cell: 1(978)-394-2867 web: http://www.towardex.com , noc: www.twdx.net
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