Re: BGP Trick: Peering Double Default Route

Good article to further read on

http://gandikitchen.net/post/2011/06/20/When-Null0-and-BGP-May-Cause-Problems

//RR

On 18 July 2012 17:14, Jose Jara <jjarafiz_at_gmail.com> wrote:

> Hi mates,
>
> I am just writing to put here a trick that I have found out after doing
> some testing in BGP peering. Let4s say we have two routers (R1&R2) directly
> connected and they're going to establish an eBGP session between their
> loopbacks.They will use update-source with the loopback and
> disable-connected check. However, the reachability is via a default route
> in each router, therefore, the BGP session can not be established:
>
> BGP: *2.2.2.2 active open failed - no route to peer*, open active delayed
> 32091ms (35000ms max, 28% jitter)
>
> What I thought was, how could they go ahead and establish the session
> without changing the routing? What if I install a route to the loopback
> pointing to null 0 to bypass the BGP check and then, remove it ?
> I tested it and surprisingly it worked! Look at that:
>
> *R1(config)#ip route 2.2.2.2 255.255.255.255 null 0
> *R1(config)#
> *Mar 1 00:05:11.751: BGP: 2.2.2.2 open active, local address 1.1.1.1
> *R1(config)#no ip route 2.2.2.2 255.255.255.255 null 0
> *R1(config)#
> *Mar 1 00:05:17.843: BGP: 2.2.2.2 went from Active to OpenSent
> *Mar 1 00:05:17.847: BGP: 2.2.2.2 sending OPEN, version 4, my as: 100,
> holdtime 180 seconds
> *Mar 1 00:05:17.851: BGP: 2.2.2.2 send message type 1, length (incl.
> header) 45
> *Mar 1 00:05:17.903: BGP: 2.2.2.2 rcv message type 1, length (excl.
> header) 26
> *Mar 1 00:05:17.907: BGP: 2.2.2.2 rcv OPEN, version 4, holdtime 180
> seconds
> *Mar 1 00:05:17.907: BGP: 2.2.2.2 rcv OPEN w/ OPTION parameter len: 16
> *Mar 1 00:05:17.907: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2
> (Capability) len 6
> *Mar 1 00:05:17.907: BGP: 2.2.2.2 OPEN has CAPABILITY code: 1, length 4
> *Mar 1 00:05:17.907: BGP: 2.2.2.2 OPEN has MP_EXT CAP for afi/safi: 1/1
> *Mar 1 00:05:17.911: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2
> (Capability) len 2
> *Mar 1 00:05:17.911: BGP: 2.2.2.2 OPEN has CAPABILITY code: 128, length 0
> *Mar 1 00:05:17.911: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability(old)
> for all address-families
> *Mar 1 00:05:17.911: BGP: 2.2.2.2 rcvd OPEN w/ optional parameter type 2
> (Capability) len 2
> *Mar 1 00:05:17.911: BGP: 2.2.2.2 OPEN has CAPABILITY code: 2, length 0
> *Mar 1 00:05:17.915: BGP: 2.2.2.2 OPEN has ROUTE-REFRESH capability(new)
> for all address-families
> BGP: 2.2.2.2 rcvd OPEN w/ remote AS 200
> *Mar 1 00:05:17.915: BGP: 2.2.2.2 went from OpenSent to OpenConfirm
> *Mar 1 00:05:17.915: BGP: 2.2.2.2 went from OpenConfirm to Established
> *Mar 1 00:05:17.915: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up
>
> Just for fun!
>
>
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Received on Wed Jul 18 2012 - 17:29:58 ART