Re: BGP Trick: Peering Double Default Route

Sud,

If the only route to reach the neighbor is the default route, a router
will not attempt to connect to it. I wrote a blog about it few years
back:

http://blog.ipexpert.com/2010/11/08/bgp-peering-and-default-routes/

By the end of the article, I address the double-default problem in a
slightly different fashion than posted here. My solution would work
after a reload though ;-).

--
Marko Milivojevic - CCIE #18427 (SP R&S)
Senior CCIE Instructor - IPexpert
On Thu, Jul 19, 2012 at 5:30 PM, Sud <mitsuie2_at_gmail.com> wrote:
> Hi Jose,
>
> I don't understand why it is not working with default routes at each end.
>
> Sud
>
> Sent from my iPad
>
> On Jul 18, 2012, at 5:29 PM, Raghava Rao <raghava.rao85_at_gmail.com> wrote:
>
>> 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!
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
Blogs and organic groups at http://www.ccie.net