From: Debashis Kundu (dkundu@xxxxxxxxx)
Date: Mon Sep 17 2001 - 00:11:26 GMT-3
Please read the case study on page 728 of Doyle's routing TCP/IP
At 09:34 PM 9/16/2001 -0400, Nigel Taylor wrote:
>Deb,
> See Inline..
>
>----- Original Message -----
>From: "Debashis Kundu" <dkundu@cisco.com>
>To: "Nigel Taylor" <nigel_taylor@hotmail.com>
>Cc: "Cade Wagner" <cwagner@logosinc.com>; <ccielab@groupstudy.com>
>Sent: Sunday, September 16, 2001 8:59 PM
>Subject: Re: OSPF Area Summary Question
>
>
> > Sorry I think you misunderstood. I am talking about the range command(ABR)
> > not summary-address(ASBR).
> > Please check the original problem.
>
>NT: Ok.. this problem as restated by the original post..
>-------------
>The problem is indeed that I don't have a subset of area 1 in the
>range of 10.1.1.0/24. Maybe I am approaching the problem incorrectly. How
>then do I advertise a range that isn't included in an OSPF area to OSPF
>Routers without redistribution, without statics, and without adding the
>outside range to an OSPF area? Thinking about it I guess that I could add a
>loopback to this range and then use the area range command. Any thoughts?
>Thanks.
>
>Cade Wagner
>----------------
>
> >
> > In the ABR whenever summary routes are configured using range command it's
> > better to add a static route with null interface also because if you have
> > default route advertised by some other area this will avoid creating a
> > routing loop.
>
>NT: I understand that this is an ABR and the need to summarize a specific
>network into the ospf
>routing domain. There really isn't any difference in implementation in that
>the "area range" and
>using the static option you describe except that one is static and one is
>dynamic in that if changes occur
>within the network as it pertains to the information required to generate
>the summarized route(a type 3 LSA)
>then, the ABR would no longer advertise this summary route. With the speed
>at which ospf converges if this
>situation was to happen I still don't think you would see a routing issue.
>Even, as you mentioned with the area
>receiving a default route from somewhere within the ospf routing domain.
>
>I think this would come down to a difference between what some of my
>co-workers and I discussed recently..
>
>Effectiveness and Efficiency
>
>Nigel
>
>
> >
> > Please let me know if you need more explanation.
> >
> > Deb
> >
> > At 08:28 PM 9/16/2001 -0400, Nigel Taylor wrote:
> > >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
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