From: Peter van Oene (pvo@usermail.com)
Date: Mon Apr 12 2004 - 10:54:38 GMT-3
At 09:42 AM 4/12/2004, Richard Dumoulin wrote:
>Ah ok I understand, let me copy/paste an e-mail I sent to Allan yersteday.
>It is not about a production network but a CCBootcamp scenario in which
>configuring the wild card mask was not doing the job:
Right. So what is the forwarding address in each of these cases? Explicit
to .2 in the first, and 0.0.0.0 in the second I'd imagine?
Also, what are the implications if .2 is reachable, but by another
protocol, say eigrp to the rest of a multi-area OSPF domain. Really some
interesting stuff comes into play here that all deal with how the
forwarding address is set, and further what the restrictions are for using
type 5's with various forwarding addresses (ie you must be able to resolve
the forwarding address via an OSPF inter area route).
Just trying to get some theory to the list, vs another memorized command.
>From: Richard Dumoulin
>[<mailto:richard.dumoulin@vanco.es>mailto:richard.dumoulin@vanco.es]
>Sent: Monday, April 12, 2004 6:39 AM
>To: Allan Wells
>Subject: RE: advertise ospf as 192.168.1.1 /29 0.0.0.0 area 0 and no t
>0.0.0.7
>
>
>
>Allan,
>
>It's CCBootcamp scenario5.
>
>Suppose 2 routers: R5 and R2 connected by ethernet (so it is a broadcast
>media, very important)
>
>OSPF is configured between them and the rest of the ospf cloud is behind
>R5. So we have the following diagram:
>
> OSPF CLOUD <---> R5 <--OSPF--> R2
>
>The network between R2 and R5 is 137.20.20.0/24.
> R5 is 137.20.20.10 and R2 is 137.20.20.1
>
>There is a default route on R2 --> ip route 0.0.0.0 0.0.0.0 137.20.20.2
>
>Also 137.20.20.2 host does not exist but the scenario asks to configure
>this anyway :))
>
> ----------------------
>
>The question says to announce the default route to the ospf cloud. This is
>done by configuring "default-information originate" on R2. Now R2 becomes
>an ASBR ok ?
>
>Here comes the issue: if on R2 I configure "network 137.20.20.0 0.0.0.255
>area 0" like I usually do then the default route will show on R5 like this:
>
>O*E2 0.0.0.0/0 [110/1] via 137.20.20.2, 02:24:11, Ethernet0/0
>
>Do you remember ? 137.20.20.2 does not exist !! And there is a loopback
>on R2 which does not belong to any protocol so the ospf cloud won't be
>able to reach it. And a requirement is to have connectivity to any ip
>address !!
>
>Now if instead I configure R2 like this: "network 137.20.20.1 0.0.0.0
>area 0" then R5 will see the default route like this:
>
>O*E2 0.0.0.0/0 [110/1] via 137.20.20.1, 02:24:11, Ethernet0/0
>
>137.20.20.1 is the asbr itself (R2) and now R5 and the ospf cloud will
>reach R2's Loopback0
>
>
>
>Allan, this is explained in the Netmasterclass paper. Just take some
>routers and practice the scenario. Let me know if it has been helpful,
>
>Regards,
>
>--Richard
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