From: Peter Grewal (peter@avient.ca)
Date: Mon Apr 07 2008 - 23:19:01 ART
Chris,
I really appreciate the help, in playing around with it that is indeed what
appears to be happening. I got stuck on the fact that R1 only forwards the
best routes, which now makes sense. I was assuming it would be like OSPF,
where all the routers had the same routes within the same area.
Thank you.
Peter.
-----Original Message-----
From: Chris McGuire [mailto:cmcguire@firstdigital.com]
Sent: Monday, April 07, 2008 9:34 PM
To: Peter Grewal; 'Smith, Jason'; 'Cisco certification'
Subject: Re: Question about BGP and setting local preference
So, are we in agreement as to what the functionality is? If you are
injecting routes in from the BB's who are of the same AS. Your R2 is acting
as it should by only forwarding the routes to either R1 or R3 depending on
what routes it adds to it's own route table. R2 will not send routes from R1
to R3 if it does not choose these routes as the best routes and vice versa.
What you originally described is correct.
So, if you change the Local pref to 200 on R1, you should only have the BB
routes on R1 out to bbX and 2 routes on R3 - 1 to the BB and the other to
R2. If you change the Local pref to 200 on R3 and change R1 back to default
you should see the exact same thing but vice versa.
I hope this helps. Please explain if there is anything missing from the
puzzle.
Thanks,
Chris
On 4/7/08 6:49 PM, "Peter Grewal" <peter@avient.ca> wrote:
> Theres a couple of different routes that I add to one and not the others,
> there 10 other routes that are the same. These mutually exclusive routes
> show up on both routers.
>
> Peter.
>
> -----Original Message-----
> From: Smith, Jason [mailto:JASmith@nuvox.com]
> Sent: Monday, April 07, 2008 7:06 PM
> To: Chris McGuire; Peter Grewal; Cisco certification
> Subject: RE: Question about BGP and setting local preference
>
> Does BB1 and BB2 advertise the same routes??
> Thanks,
> Jason Smith
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Chris McGuire
> Sent: Monday, April 07, 2008 5:27 PM
> To: Peter Grewal; 'Cisco certification'
> Subject: Re: Question about BGP and setting local preference
>
> This appears to me to be correct. On 1 side you should see both routes
> in
> the BGP table. On the other you should see only 1. What happens is R2
> receives both routes. It then chooses the best route and installs it
> into
> it's Route table. If the "Best" route is coming from R1, it will forward
> that route on to R3. If the "Best" route is coming from R3, it will
> forward
> that route on to R1. R2 will not take a route from R3 and forward it on
> to
> R1 if it is not a route that it can install in it's own route table. So
> on 1
> side, you should only see 1 route - the EBGP route. ON the other, you
> should
> see the EBGP route and 1 IBGP route in the bgp table. Unless I am
> missing
> something, you are seeing it work as it should.
>
> -Chris
>
>
> On 4/7/08 1:06 PM, "Peter Grewal" <peter@avient.ca> wrote:
>
>> Just trying to figure out something that I'm seeing in BGP, and
> determine
>> whether its normal behavior or not.
>>
>>
>>
>> Suppose I have routers BB1----R1 --------R2-----R3----BB2
>>
>>
>> |
>>
>>
>> R4
>>
>>
>>
>> R1, R2, R3, R4 are all in the same AS, BB1 and BB2 are in the same AS.
> I
>> have applied a local preference specifying all routes learned from the
>> external AS are preferred through R3 with a value of 200, routes
> learned
>> from R1 have a local pref for the external AS specified to 150. After
>> applying the corresponding access list to both R1 and R3, when I
> perform a
>> show IP BGP on R3 I no longer see routes for that are advertised by
> BB1
>> through R1. Is this normal behavior ???
>>
>>
>>
>> Thank you.
>>
>>
>>
>> Peter.
>>
>>
> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
> This email and any attachments ("Message") may contain legally privileged
> and/or confidential information. If you are not the addressee, or if this
> Message has been addressed to you in error, you are not authorized to
read,
> copy, or distribute it, and we ask that you please delete it (including
all
> copies) and notify the sender by return email. Delivery of this Message
to
> any person other than the intended recipient(s) shall not be deemed a
waiver
> of confidentiality and/or a privilege.
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Thu May 01 2008 - 08:25:50 ART