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Split Horizon from two different books

Unanswered Question
Aug 4th, 2006
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The link below from CCNA Curriculum

http://img134.imageshack.us/img134/9462/splithorizonbi7.jpg


Please see the link above and compare it with the enclosed attachment (from CCIE Professional Development Troubleshooting IP Routing Protocols Book).


Thanks



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devang_etcom Fri, 08/04/2006 - 03:55
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hi zillah...


both the artical are correctly describing the Split Horizon idea... acutlly split horizon means router doesnot send the updat to the same router from which router receive the same update... as per you attachment... and the link you send is with the close loop path here... i think your confusion is that... as router doesnot send the receive update back to the same router from where it receive the update...but here in case of close loop path RouterB, routerB have update of network1 from router A with less metric and router B will have the path to the network 1 with the higher matrics... now router B will install best path means higher metrics... so Router B will install update with low metrics which is learn from the router A and when this path goes down then it will select higher cost path... so this is how it will work ...


you can have more clear idea about it form split horizon with the poision revers...http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci939694,00.html


hope this will help


regards

Devang

farkascsgy Fri, 08/04/2006 - 03:55
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Hello,


I checked the docs and I prefer the first doc (on the link). Please memorize the first...


In the second there is a mistake as you realized...

Router 1 can't send update about Network X back to Router 2.


bye

FCS


Please rate me if I helped.


devang_etcom Fri, 08/04/2006 - 04:02
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no its true...


as per split horison router which receive update from the other router will not send the updat to the same router from which it receive the update...


try to understand split horizion with router posioning and reverse poisioning... it will clear you more...


please rate the all helpfull post..


regards

Devang

farkascsgy Fri, 08/04/2006 - 04:17
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Devang,


Is it really true?


I think is true like this context (please correct if not):

If split horizon is enabled, Router 1 will not advertise the Network X route back to Router 2 over the same serial interface. If split horizon is disabled, Router 1 will advertise Network X back to Router 2.


bye

FCS


Please rate me if I helped.

devang_etcom Fri, 08/04/2006 - 04:27
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see here


yes your understanding is true...


look at this...

router1---------router2---network X


in above topology... when router2 send update of the networkX to router1... if you disable splite horizon on router1 then it will send the update of networkX to router2 back...

if you enable the split horizion then router 1 will not send the update of networkX to the router 2 ...


rate this post if it helps


regards

Devang

farkascsgy Fri, 08/04/2006 - 04:31
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OK, Devang but in the second doc there is different statement, please check it again... (Router 1 and Router 2 are reversed)


bye


FCS


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devang_etcom Fri, 08/04/2006 - 04:39
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okay will you please explaing your concept regarding to the same document so we can discuss it more clearly...


regards

Devang

zillah2004 Fri, 08/04/2006 - 04:40
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Thanks .


Do you agree that there is a mistake (The author should have said R1 instead of R2) in the attached word document (not the link) ?

farkascsgy Fri, 08/04/2006 - 04:44
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Devang,


I think this is the true:


If split horizon is enabled, Router 1 will not advertise the Network X route back to Router 2 over the same serial interface. If split horizon is disabled, Router 1 will advertise Network X back to Router 2.


Instead of this what is in the book:

If split horizon is enabled, Router 2 will not advertise the Network X route back to Router 1 over the same serial interface. If split horizon is disabled, Router 2 will advertise Network X back to Router 1.


bye

FCS


Please rate me if I helped.


devang_etcom Fri, 08/04/2006 - 04:49
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ya that is wrong one... but what ever we disscussed is true...


rate this post if it hleps


regards

Devang

farkascsgy Fri, 08/04/2006 - 04:53
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Devang,


So I was right in my first comment, in the second doc there is a typo. Am I right, anyway if you change Router 1 to Router 2 and vice versa the second doc are also OK.


bye

FCS


Please rate me if I helped.

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