From: Nick Griffin (ngriffin@sio.midco.net)
Date: Thu May 25 2006 - 23:03:43 ART
I'm referring to this book:
http://www.amazon.com/gp/product/0321127005/sr=8-1/qid=1148608946/ref=pd_bbs_1/103-7514751-6287838?%5Fencoding=UTF8
I've read it on safari.oreilly.com.
HTH
Vishal Patel wrote:
> Are you talking about CCIE pratical studies vol II or about Internet
> Routing Arch by Halabi ?
>
> I don't have any book called pratical bgp book ?
>
> Anyways thanks for clearing the doubt.
>
> Cheers
>
> -----Original Message-----
> From: Nick Griffin [mailto:ngriffin@sio.midco.net]
> Sent: Friday, 26 May 2006 10:30 AM
> To: Vishal Patel
> Cc: ccielab@groupstudy.com
> Subject: Re: Routing issue
>
> It sounds to me like you were running into next hop recursion oscillation.
> Check out the practical bgp book:
>
> "The BGP process will then revert the route back to the bestpath through
> router C, and the next time the BGP scanner process runs, the route will
> switch the router to the path through router B. This will continue, every 60
> seconds.
>
> The problem here is not that the route to the next hop is learned via iBGP,
> but rather the route to the next hop recurses through the route itself,
> which is impossible. There are several possible solutions to this problem:
>
> *
>
> Include the next hop, in this case 10.1.1.1, in the interior
> gateway protocol so it is not learned through iBGP. This breaks
> the recursion of the route onto itself.
>
> *
>
> Create a static route to the next hop from router A. This also
> breaks the recursion by providing another path to the route's next
> hop than through the route itself.
>
> *
>
> Configure router C to set the next hop for all routes it is
> advertising to itself using the Cisco IOS software command
> neighbor <x.x.x.x> next-hop-self. This breaks the recursion of the
> route by changing the next hop so it's not part of the route being
> learned."
>
>
> Vishal Patel wrote:
>
>> Hi ,
>>
>> Got it fixed.
>>
>> The problem was , I was accepting only default route in IGP.
>>
>> The BGP's neigbour was also not accepted in the filter.
>>
>> I added the IBGP neigbour in the filter and the things are looking
>> fine now.
>>
>> But I don't know the reason , why the routes where flip flopping.
>>
>> If the router was not having the route for the BGP neighbour , then
>> the BGP session shouldn't have established at all.
>>
>> Any ideas ?
>>
>> Cheers
>>
>> Vishal
>>
>> -----Original Message-----
>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
>> Of Nick Griffin
>> Sent: Thursday, 25 May 2006 11:15 PM
>> To: Vishal Patel
>> Cc: ccielab@groupstudy.com
>> Subject: Re: Routing issue
>>
>> I would venture to say that if you did a "show ip bgp x.x.x.x" before
>> the routes flip to IGP, that the next hop would be marked as
>> inaccessible. Have or can you verify this? It's possible you have a
>> next hop recursion problem causing the routes to be installed and
>> removed by the scanner process when the next hop is marked inaccessible.
>>
>> Vishal Patel wrote:
>>
>>
>>> Hi all,
>>>
>>> Iam facing a weird problem.
>>>
>>> I have a router running ospf and ibgp.
>>>
>>> And i have a distribute-list which allows only a default route from
>>> the neigbour in ospf domain.
>>>
>>> And Iam accepting all the internal routes via IBGP.
>>>
>>> My routing table should show the internal routes via IBGP with the
>>> metric of 200.
>>>
>>> But the problem happening is the routing updates are continously
>>> changing between ospf and bgp.
>>>
>>> for a movement I get only default route via ospf and next movement I
>>> get all the internal routes via IBGP.
>>>
>>> As soon as remove distribute-list from ospf and accept the whole
>>> network via ospf , the things are stable.
>>>
>>> Well i also have more ospf neigbour , to a different router but it
>>> has higher cost and it never appears in the routing table.
>>>
>>> Any ideas ?
>>>
>>> Cheers
>>>
>>> Vishal
>>>
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