Re: EIGRP - Split Horizon

Good point about split horizon, but these routes should be in the topology table, but only one route to R1 in routing table, right?

Regards,
Jay McMickle- CCNP,CCSP,CCDP
Sent from my iPhone
http://mycciepursuit.wordpress.com

On Jan 8, 2011, at 5:04 PM, Scott M Vermillion <scott_ccie_list_at_it-ag.com> wrote:

> The nuance I was referring to was more the "interface >that the router
> itself uses< to reach the destination." A traditional definition of
> split horizon would hold that a router is not to advertise a route out
> of an interface through with it learned of of that same route.
> According to that definition, depending on the timing of things, R3
> would advertise R1's Lo0 to R4 - or the other way around - and then
> the learning router would not advertise R1's Lo0 back to the other
> neighbor. What Dave noticed was that this wasn't actually what was
> happening: both R3 and R4 were advertising R1's Lo0 to each other.
> This is all perfectly fine and acceptable, because both R3 and R4 are
> presumably using a path directly via R2. Now if you go and jack up
> the cost on R3 or R4 via R2, you might see a different result...
>
>
> On Jan 8, 2011, at 3:55 , jules NYA BAWEU wrote:
>
>> I believe the key word is out of the "interface" the route was
>> learned from. R4 sure receives the route from R2 also - same route
>> but different metric and path - check the topology table, you will
>> sure see that they have different metrics
>>
>> On Sat, Jan 8, 2011 at 10:05 AM, Scott M Vermillion <scott_ccie_list_at_it-ag.com
>>> 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
>>>
>>>
>>> Blogs and organic groups at
>>> http://www.ccie.net
>>>
>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>>
>>>
>>> Blogs and organic groups at http://www.ccie.net
>>>
>>>
>> _______________________________________________________________________
>>> Subscription information may be found at:
>>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html

Blogs and organic groups at http://www.ccie.net
Received on Sat Jan 08 2011 - 18:01:09 ART