From: Nigel Taylor (nigel_taylor@xxxxxxxxxxx)
Date: Sun Sep 16 2001 - 21:28:28 GMT-3
Debashis,
See Inline...
----- Original Message -----
From: "Debashis Kundu" <dkundu@cisco.com>
To: "Cade Wagner" <cwagner@logosinc.com>; <ccielab@groupstudy.com>
Sent: Sunday, September 16, 2001 7:34 PM
Subject: Re: OSPF Area Summary Question
> 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.
Why would you add a static route to the null0 interface? Typically when the
summary-address command is used it is done to pass/inform the OSPF
routing domain about an external network. For the summary-route to be
generated the router(typically an ASBR) must have a route for the network
being summarized in it's local RIB. When the summary route(a type 5 LSA) is
generated a route to null0 is placed into the local RIB to maintain the
integrity of the routing information. Hence no need to create static
routes.
>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.
Short of being a stub, totally-stubby and a NSSA If all routers in the OSPF
domain does not have the summary-route generated form the ASBR performing
the summarization then you may a bigger problem in that all OSPF routers
within normal/typical areas should synchronize and have identical Link-State
databases. I think placing static routes to null0 in this case could
complicate things for not so experienced network personnel. Now it will
happen that if the router(ASBR) performing the summarization for some reason
or another loses the route for the network being summarized then, yes the
issue you mentioned would exist in which case none of the routers within the
ospf domain will have a route for the specific network. In this case a
typical 0/0 (default route or static route to the specified network) could
possibly provide the connectivity to this otherwise reachable network.
Anyone care to make any suggestions...or share possible experiences.
Nigel
>
>
> 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
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:32:19 GMT-3