From: Tony Schaffran (groupstudy@cconlinelabs.com)
Date: Sun Aug 08 2004 - 14:53:04 GMT-3
I work for an ISP and the preferred method for multi-homed BGP is
update-source loopback with the multi-hop set to the minimal hop count to
reach the peer. You should not be using multi-hop=255, I agree. In our
experience, it is actually the reverse, we have had bad situations where
update-source loopback is not used. If one of the interfaces is being used
as the BGP source and it goes down, say it is the other provider link and
not the directly connected link to you, your BGP session goes down. You
still have connectivity, but no BGP. Yes, there are ways to ensure this
does not happen, but the most simple straight forward way is to use
update-source loopback.
Anyway, this string has gone way off the point of the LAB. For lab
purposes, it is best to use update-source loopback. Do not try to
rationalize the lab with what is done in real life. If you do that, you
will be scheduling you re-test.
Just my two cents.
Cheers,
Tony Schaffran
Network Analyst
CCIE #11071
CCNP, CCNA, CCDA,
NNCDS, NNCSS, CNE, MCSE
www.cconlinelabs.com
Your #1 choice for online Cisco rack rentals.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
jongsoo.kim@intelsat.com
Sent: Sunday, August 08, 2004 9:26 AM
To: ccielab@groupstudy.com
Subject: Re: RE: BGP Update Source
Just my two cents on why EBGP peering w/ multihop, update source is not
recommended.
In real ISP life, EBGP session with multihop = 255 and update source
loopback can be really "dangerous" config as this can create all kind of
problems( black hole, BGP session never being down when it supposed to be)
specially if the customer's( the other bgp peer) loopback is reachable
without bringing up the physical connection ( so customer has multi-homed
and loopback address is reachable via the other ISP link as well).
It is only recommended for load-balance with ttl= 2 or whatever necessary
minimum number. However, in a simplex satellite VSAT network commonly use
eBGP w/ multihop=255 with a great caution.
Jongsoo
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