Re: EIGRP - Split Horizon

Also Dave, I don't know about you but I tend not to be able to hold
onto little facts like this unless I play with them in a lab. So, for
example, I might go and jack up the cost on R3's interface toward R2
such that R3 chooses the path via R4 instead. Then have a look at
R4's topology table (and also R2's!). I would do and post the results
but my lab is right in the middle of doing something else at the
moment...

On Jan 8, 2011, at 11:05 , Scott M Vermillion wrote:

> Hey Dave,
>
> There's a nuance in the description of EIGRP split horizon in the
> command ref:
>
> http://www.cisco.com/en/US/docs/ios/iproute_eigrp/command/reference/ire_s1.html#wp1058799
>
> "The split-horizon rule prohibits a router from advertising a route
> through an interface that the router itself uses to reach the
> destination."
>
> I'm guessing neither R3 nor R4 use the other to reach R1's Lo0,
> correct?
>
> Cheers,
>
> Scott
>
>
>
> On Jan 8, 2011, at 10:54 , Dave Serra wrote:
>
>> Hi Guys,
>>
>> I thought I understood the split horizon rule until I built the
>> following topology in GNS:
>>
>> R3---------R4
>> | ----R2----|
>> |
>> R1
>>
>> What I'm trying to depict in the above diagram is a triangle
>> topology between
>> R2, R3, and R4. R1 hanging off of R2 outside the triangle.
>> All routers are running EIGRP on all interfaces. I create a
>> loopback of
>> 1.1.1.1/32 on R1. I then see the route travel from R1 to R2, from
>> R2 to R3
>> and
>> R4 and finally (and most confusingly) from R3 to R4 and from R4 to
>> R3.
>> It is this last part that I am having trouble with. When R3 learns
>> the
>> route of
>> 1.1.1.1/32 from R2 and sends it to R4, shouldn't R4 NOT send that
>> same route
>> back to R3 due to split horizon???
>>
>> I show in the 'show ip eigrp
>> top all' on both R3 and R4 that this route is
>> learned from each other.
>>
>> Can
>> someone help me to better understand this?
>>
>> Thanks in advance :)
>>
>> Dave
>> Make a small loan, Make a big difference - Kiva.org
>> ________________________________
>> From: Juan <fferrer10_at_gmail.com>
>> To: Cisco
>> certification <ccielab_at_groupstudy.com>
>> Sent: Fri, January 7, 2011 1:35:34 AM
>> Subject: Test, Please ignore
>>
>> Test
>>
>>
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Received on Sat Jan 08 2011 - 11:23:55 ART