I poked around and found the following links and I have copied some of what
you will find there.
http://www.support.baynetworks.com/library/tpubs/html/switches/bstream/11540
1A/L_61.HTM#MARKER-9-718
Enabling Multihop Connections
By default, BGP enforces the one-hop rule for BGP peers -- the remote peer
must be located on a directly attached network.
You can use Site Manager to override the restriction and allow multihop
connections.
Caution: Enabling multihop BGP connections is dangerous because it can
cause BGP speakers to establish a BGP connection that traverses a
third-party AS, which may violate policy considerations and may also
introduce forwarding loops.
And this...
http://www.support.baynetworks.com/library/tpubs/html/switches/bstream/11540
1A/L_91.HTM#MARKER-9-911
Parameter: Multi-hop EBGP Connection
Path: Configuration Manager > Protocols > IP > BGP > Global
Default: Disable
Options: Enable | Disable
Function: Specifies whether BGP allows multihop connections to an external
BGP peer.
Instructions: By default, BGP enforces the rule that requires an external
BGP peer to be located on a directly attached network. Use this parameter to
override the restriction. Enabling multihop BGP connections is dangerous
because it can cause BGP speakers to establish a BGP connection that
traverses a third-party AS, which may violate policy considerations and may
also introduce forwarding loops.
MIB Object ID: 1.3.6.1.4.1.18.3.5.3.2.5.1.1.6
"Chuck Larrieu" <[EMAIL PROTECTED]> wrote in message
001501c0263f$53d902e0$[EMAIL PROTECTED]">news:001501c0263f$53d902e0$[EMAIL PROTECTED]...
> Interesting theory. The RFC states ( as does Halabi ) that eBGP peers must
> be on the same subnet. I wonder if the ebgp-multihop is a Cisco thing?
Kinda
> along the lines of ip unnumbered?
>
> Chuck
>
> -----Original Message-----
> From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
> Andrew Smith
> Sent: Thursday, September 14, 2000 12:57 PM
> To: Hubert Pun; [EMAIL PROTECTED]
> Subject: Re: BGP Loopback Update-source
>
>
> Given:
>
> ------------------
> router a:
>
> int fast 0/0
> ip address 10.0.0.1 255.0.0.0
>
> int loop 0
> ip address 172.16.0.1 255.255.0.0
>
> router bgp 1
> neighbor 172.17.0.1 remote-as 2
> neighbor 172.17.0.1 update-source fast0/0
>
> ------------------
> router b:
>
> int fast 0/0
> ip address 10.0.0.2 255.0.0.0
>
> int loop 0
> ip address 172.17.0.1 255.255.0.0
>
> router bgp 2
> neighbor 10.0.0.1 remote-as 1
> neighbor 10.0.0.1 update-source loop 0
> ------------------
>
> Router A will not show a direct route to 172.17.0.1, does not have
> ebgp-multihop enabled, and will thus not INITIATE the TCP connection
> to router B.
>
> Router B will show a direct route to 10.0.0.1 and thus will initiate
> the TCP connection to Router A. Apparantly ebgp-multihop only applies
> to whether or not to attempt an active open. If a configured neighbor
> initiates a connection to us, and we have any type of route to his
> source IP, we'll go ahead and negotiate it. This is an educated guess
> on my part. If it's possible to set a peer status to "listen and accept,
> but don't initiate", you could test this theory.
>
> On 14-Sep-2000, Hubert Pun wrote:
> > Regarding about my BGP update source problem, I get suggestion that I
need
> to
> > use the ebgp-multihop. However, if I just use loopback on one side and
> direct
> > neighbor on the other side, it works perfectly without the multihop
> statement.
> > Why do I need that statement if I am using loopback on both sides
instead
> on
> > one side?
> >
> > Thanks in advance
> >
> > Hubert
> >
> > Andrew Smith wrote:
> >
> > > Since you have the routers in different AS's, they are using eBGP
> > > instead of iBGP. If the peer addresses aren't on a directly connected
> > > network, you need the following command on both routers:
> > >
> > > neighbor x.x.x.x ebgp-multihop
> >
> >
> > **NOTE: New CCNA/CCDA List has been formed. For more information go to
> > http://www.groupstudy.com/list/Associates.html
> > _________________________________
> > UPDATED Posting Guidelines: http://www.groupstudy.com/list/guide.html
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>
> --
> --------------------------------------------------------------------------
-
> ** Andrew W. Smith ** [EMAIL PROTECTED] ** Chief Network Engineer **
> ** http://www.neosoft.com/neosoft/staff/andrew ** 1-888-NEOSOFT **
> ** NeoSoft, Inc. An Internet America Company 1-800-BE-A-GEEK **
> ** "Opportunities multiply as they are seized" - Sun Tzu **
> --------------------------------------------------------------------------
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>
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