Re: EIGRP - Split Horizon

Yessir, under normal circumstances, that would probably be correct. I
think you could play with metrics and variance and come up with a
different result (on just one of the two routers in question - R3 _or_
R4 - at any given time), though...

On Jan 8, 2011, at 5:01 , Jay McMickle wrote:

> 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 - 17:10:09 ART