forwarded msg. Geoff Huston <gih at telstra.net>

[Charles Musisi <cmusisi at cfi.co.ug>]

ate: Wed, 16 Apr 2003 19:44:09 +1000
To: Joe Joe <yhovluv at yahoo.com>, Brian Candler <B.Candler at pobox.com>
From: Geoff Huston <gih at telstra.net>
Subject: Re: BGP over satellite link
Cc: afnog at afnog.org
In-Reply-To: <20030406153029.78641.qmail at web20713.mail.yahoo.com>
References: <20030405132139.GA12180 at uk.tiscali.com>
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Does this help?

http://www.potaroo.net/ispcolumn/2000-03-simplex.html


    Geoff


At 08:30 AM 4/6/2003 -0700, Joe Joe wrote:

 > >How exactly do you mean "we are not directly connected?" Normally you would
 > >have a border router which connects to the leased line or satellite link,
 > >and at the other end of the link is your provider's border router. If this
 > >is not what you are intending to have, can you draw an ASCII diagram?
 >I am connected via a satellite link (SCPC/DVB). I have my border router
 >and definitely does my provider as well.
 >
 > >Well, this is by agreement with your provider. Normally it makes sense to
 > >use your router interface IP (typically assigned by your provider as a /30
 > >subnet). This is so that if the link fails, the BGP keepalives will fail to
 > >get through. BGP will thus notice the failed link, withdraw the routes, and
 > >your traffic will get rerouted via your other provider. You don't want the
 > >BGP session between yourself and provider A to be re-routed via 
provider B's
 > >link!
 >
 >I dont have a /30 between me and my provider. I have my own address space.
 >Is the bgp multihop option not a good choice for my config settings?? If
 >it is, is it best to use my IP interface address or loopback address?
 >
 >thanks
 >
 >J.
 >
 >  Brian Candler <B.Candler at pobox.com> wrote:
 >On Sat, Apr 05, 2003 at 04:04:28AM -0800, Joe Joe wrote:
 > >
 > > Hello,
 > >
 > > I'm a newbie on this list.
 >
 >Welcome!
 >
 > > I need to run BGP with my upstream provider
 > > because I will be multihomed to another provider, since we are not
 > > directly connected, how do I go about the config.
 >
 >How exactly do you mean "we are not directly connected?" Normally you would
 >have a border router which connects to the leased line or satellite link,
 >and at the other end of the link is your provider's border router. If this
 >is not what you are intending to have, can you draw an ASCII diagram?
 >
 > > Secondly, am I to
 > > use my router interface IP address or the loopback address to run the
 > > BGP session with my upstream.
 >
 >Well, this is by agreement with your provider. Normally it makes sense to
 >use your router interface IP ! (typically assigned by your provider as a /30
 >subnet). This is so that if the link fails, the BGP keepalives will fail to
 >get through. BGP will thus notice the failed link, withdraw the routes, and
 >your traffic will get rerouted via your other provider. You don't want the
 >BGP session between yourself and provider A to be re-routed via provider B's
 >link!
 >
 >However, if I remember correctly, BGP sets an IP TTL of 1 on its packets
 >anyway by default, so it should work even if you use a loopback address. In
 >that case it will try to reroute the BGP packets via provider B, but because
 >provider A's router is more than one hop away when reached via provider B,
 >the BGP session between you and provider A will still fail when the link
 >goes down.
 >
 >It can be preferential to use a loopback address in some cases, for example
 >if you are running two 2M links in parallel to the same far-end router to
 >simulate a 4M link:
 >
 >serial0 2M
 >,-----! -----------.
 >you provider
 >`----------------'
 >serial1 2M
 >In this case, you do want the BGP session to stay up even if one of the two
 >2M lines goes down, so you run it between loopbacks, with static routes to
 >the loopback address of the far-end router. If both 2M lines are up, the
 >routers will round-robin the traffic between them.
 >
 >Regards,
 >
 >Brian.
 >
 >
 >
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