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
>
>
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