From: Nigel Taylor (nigel_taylor@xxxxxxxxxxx)
Date: Sun Sep 16 2001 - 22:34:41 GMT-3
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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