[j-nsp] ISIS Case Study in JNCIP..Summarization into Backbone

[Muhammad Farooq]

Hi Hoogen,
Your understanding is perfect. When requirement is to redistribute aggregate into backbone, then it is good, infact ideal practice to suppress more specific routes although it is explicitly not required.

Regards,
Farooq
> Date: Fri, 18 Sep 2009 01:16:16 -0700
> From: hoogen82 at gmail.com
> To: juniper at groupstudy.com; juniper-nsp at puck.nether.net
> Subject: [j-nsp] ISIS Case Study in JNCIP..Summarization into Backbone
> 
> Hi,
> My question is when we redistribute 172.16.40.0/30 and 172.16.40.4/30 subnet
> on R6 and R7...it reaches R5... and we see the output as
> 
> lab at R5# run show route 172.16.40.0/29
> 
> inet.0: 29 destinations, 29 routes (29 active, 0 holddown, 0 hidden)
> + = Active Route, - = Last Active, * = Both
> 
> 172.16.40.0/30     *[IS-IS/15] 00:17:21, metric 6
>                     > to 10.0.8.5 via ge-0/0/0.0
> 172.16.40.4/30     *[IS-IS/15] 00:16:53, metric 6
>                     > to 10.0.8.10 via ge-0/0/1.0
> 
> [edit]
> lab at R5#
> 
> Now we need to summarize this before sending it into Backbone..
> 
> On R5 though we see the policy-option to be
> 
> term 3 {
>         from {
>             protocol aggregate;
>             route-filter 172.16.40.0/29 exact;
>   }
>         to level 2;
>         then accept;
>     }
> }
> 
> In this we have it accepting aggregate route 172.16.40/29
> 
> Now in the whole policy on R5 we do not discard the more specific routes
> from entering the Backbone area
> 
> And on R3 we see those three routes along with the aggregate route...
> 
> lab at R3# run show route 172.16.40.0/29
> 
> inet.0: 25 destinations, 25 routes (25 active, 0 holddown, 0 hidden)
> + = Active Route, - = Last Active, * = Both
> 
> 172.16.40.0/29     *[IS-IS/165] 00:04:07, metric 13
>                     > to 10.0.2.1 via t1-2/0/0.35
> 172.16.40.0/30     *[IS-IS/18] 00:12:15, metric 9
>                     > to 10.0.2.1 via t1-2/0/0.35
> 172.16.40.4/30     *[IS-IS/18] 00:11:47, metric 9
>                     > to 10.0.2.1 via t1-2/0/0.35
> 
> [edit]
> lab at R3#
> 
> Now from my understanding of the question I need to deny the longer more
> specific routes... on R5 filter saying 172.16.40/29 longer the reject...
> 
> So that on R3 and R4 I only see
> 
> lab at R3# run show route 172.16.40.0/29
> 
> inet.0: 23 destinations, 23 routes (23 active, 0 holddown, 0 hidden)
> + = Active Route, - = Last Active, * = Both
> 
> 172.16.40.0/29     *[IS-IS/165] 00:04:29, metric 13
>                     > to 10.0.2.1 via t1-2/0/0.35
> 
> [edit]
> lab at R3#
> 
> 
> Is my understanding right.. or is this step not required ...I do not see
> this extra solution in the book..
> 
> -Hoogen
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