From: Peter Van Oene (pvo@xxxxxxxxxxxx)
Date: Mon Sep 17 2001 - 10:18:45 GMT-3
Lets clarify this a little bit. When one summarizes, a form of default routing
takes place. Default routing can introduce situations where two parts of a ne
twork default towards each other for a particular set of aggregated prefixes.
When those prefixes become unreachable, traffic is prone to bounce between the
two areas. To address this, one can blackhole the summary addresses with a sta
tic to null0. Such a static, will only match when no more specifics exist and
thus the traffic is destined to a non available network. Instead of looping th
en, this null0 next hop will remove the traffic from the domain.
Cisco does this automatically when external summarizations are taking place, bu
t doesn't do so for inter-area summarization.
How this relates to Cade's question however is a more difficult question to ans
wer :) What Cade is trying to do might even pose a tougher question though lik
ely he's suffering from the need to do normal things in backwards ways to build
knowledge that the lab induces.
Pete
*********** REPLY SEPARATOR ***********
On 9/16/2001 at 7:34 PM Debashis Kundu wrote:
>Whenever summary routes are configured within an OSPF domain, be sure to
>add a static route for
> the summary address pointing to the null interface. This is done to
>avoid
>routing loops because it may happen that you don't have all the summary
>addresses in your area so this is just design practise.
>
>
>At 01:44 PM 9/16/2001 -0400, you wrote:
>> Not sure what I am doing wrong, but I can never get the area 1
>range
>>10.1.1.0 255.255.255.0 command to work.
>>
>> Many of the examples that I have seen have a route to Null0 for
>what
>>is summarized. Is this necessary like in BGP for advertised networks?
>Will
>>a route from another protocol like EIGRP work in its place? I have tried
>it
>>all three ways with no success. Probably just overlooking something
>simple.
>>Thanks for the help in advance.
>>
>> Cade Wagner
>>**Please read:http://www.groupstudy.com/list/posting.html
>**Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
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