Re: BGP peculiarity

Thank you all for your efforts in trying to resolve this conundrum.

I think i agree with Pavel. This can be seen as an example of the way IOS
customizes its operations without really affecting the underlying
principles.

Here also, although going by Ciscopress books, it appears that one
of the rules for exchanging BGP updates has been violated, however it can
also be seen as just another irregular tweak by the IOS to optimize its
operations more so since the AS-path loop prevention mechanism remains
unaffected by it.

Also found this web-page talking abt the same matter :

http://lxllx.blogspot.com/2010/05/ebgp-split-horizon.html
Regards,
Amit
On Mon, Sep 19, 2011 at 6:53 PM, Pavel Bykov <slidersv_at_gmail.com> wrote:

> I've seen different scenarios based on what you have described.
> For example, IOS XR does not send the routes, while IOS does. And it does
> depend on the version you're running.
> Both methods can withstand the scrutiny under RFC. Sometimes the routes are
> sent because the update group is easier to build that way (e.g. have one
> update group for 10 neighbors, with some useless routes is more efficient,
> than have precise update set pre neighbor, but use more update groups (which
> eats up CPU)).
> Also, there are commands avaiable to steer the behaviour in the way you
> need to. E.g. make IOS XR send the route anyway, even though normally it
> wouldn't send it.
>
>
>
> On Fri, Sep 16, 2011 at 2:09 PM, Amit Kumar Lohumi <getakl_at_gmail.com>wrote:
>
>> Hi All,
>>
>> Can anyone pls explain ....
>>
>> why is it that in some cases a BGP router would not advertise e-BGP
>> routes learned from a peer back to the same peer (sticking to the
>> standard rule on BGP updates).
>>
>> ... while in other cases, BGP will infact advertise the e-BGP routes
>> learned from a peer back to the same peer (although they do get
>> rejected by the originating peer because of ASN match ).
>>
>> I have made these dichotomous BGP observations on a couple of
>> different scenarios.
>>
>> Regards
>>
>>
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>
> --
> Pavel Bykov

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Received on Mon Sep 19 2011 - 21:30:14 ART