From: Paglia, John (USPC.PCT.Hopewell) (JPaglia@NA2.US.ML.com)
Date: Wed Oct 16 2002 - 18:32:27 GMT-3
I think the whole basis of this thought has to do with your next-to-last
sentence.
The 'update-source' command (and correct me if mistaken...like y'all need to
be told that!!!!) tells the neighbor router specified in the command to
observe YOUR loopback as the source of the peering relationship. Thus, the
interface that is being utilized for peering, from the point of view of the
neighbor, is not directly connected, but is at least 2 hops away, whether it
be EBGP or IBGP.
I do really think this is outdated but I just thought I'd throw it out there
and see if anyone knew for sure, and judging from the replies thus far, it
has to be an 'out-of-practice' practice.
Thanks,
John
> -----Original Message-----
> From: Joe Martin [SMTP:jmartin@capitalpremium.net]
> Sent: Wednesday, October 16, 2002 4:58 PM
> To: ccielab@groupstudy.com
> Subject: RE: EBGP Multihop's necessity with loopback addresses
>
> If you use a local interface or a physical interface ip address in your
> bgp
> neighbor statement then you would lose your peering if the interface or
> network goes down, even if there is another route to the bgp neighbor.
> this
> is why it is suggested that you use the loopback ip as your update source
> and specify the loopback address in your neighbor statements. This way,
> if
> your direct connection to your bgp neighbor goes down you can still
> maintain
> the neighbor relationship. However, now your neighbor is not neccessarily
> 1
> hop way. So this is where the ebgp multi-hop command comes in.
>
> Someone correct me if i'm wrong.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> Paglia, John (USPC.PCT.Hopewell)
> Sent: Wednesday, October 16, 2002 2:01 PM
> To: 'ccielab@groupstudy.com'
> Subject: EBGP Multihop's necessity with loopback addresses
>
>
> I recently heard that if you are establishing your BGP neighbors using
> 'update source loopback 0', you should also use the 'ebgp-mu' cmd, even if
> the neighbors are directly connected...the reason being that your loopback
> is NOT directly connected to the neighbor. However, in my experiments I
> have
> never done this for neighbors that are directly connected, yet have
> established peerings successfully.
>
> Is there validity to this statement, and if so, under which circumstances
> is
> it absolutely vital, other than the 'non-physically or nbma topology'
> scenarios??? Something tells me that this may be an older IOS issue or
> something like that.
>
> John
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