From: Chris McGuire (cmcguire@firstdigital.com)
Date: Mon Apr 07 2008 - 23:24:02 ART
Absolutely. Always a fun time trying to expand understanding.
On 4/7/08 8:19 PM, "Peter Grewal" <peter@avient.ca> wrote:
> 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.
>>>
>>>
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