From: Nick Shah (nshah@connect.com.au)
Date: Thu Sep 05 2002 - 02:10:10 GMT-3
Further to what has already been discussed :
The question to ask yourself and the proctor is what is allowed and what is
not ?
* Check if default network is permitted, if so, and if you can get a
classful network to play with, nothing better.
* Check for all possibilities of generating area-ranges & summaries (Area
range is possible only on ABRs and summary is possible only on ASBR), So if
a router is not an ABR, think if you can make it one, or if its not an ASBR
can you make it one. In this case (especially one mentioned below) you can
use 172.16.0.4/30 assign it to a dummy interface, do a redistribution
(connected etc.) and make an ASBR, and then do the summary stuff. This would
only work if the other subnets of 172.16.0.0/24 are not in use elsewhere.
* Check if the topology permits creating area ranges, mostly it does, and
that will save the day.
* With RIP , secondary addressing work well. Because you can have RIP honour
the secondary address masks, and also learn addresses with those masks on
the other side. With IGRP, its ugly, you have to be careful, mostly if used
on both ends it summarizes to the mask of the primary ip address. (I still
have to try what Dmitry has mentioned here)
* Tunnels have been suggested by Faraz Shamim, author of T'shooting IP
routing protocols as appropriate when dealing with IGRP especially.
* Then there are other 'dirty tricks', of creating second instance of OSPF,
redistributing into the first one. But that is mostly done to create an
ASBR.
So the trick when using OSPF is to see how you can get it to cough up
'summaries' whether by making it ABR or ASBR or tunnels or secondary
addressing.
rgds
Nick
----- Original Message -----
From: "Volkov, Dmitry (Toronto - BCE)" <dmitry_volkov@ca.ml.com>
To: "'Omer Ansari'" <omer@ansari.com>
Cc: <frank.yu@japan.bnpparibas.com>; <ccielab@groupstudy.com>
Sent: Thursday, September 05, 2002 2:03 PM
Subject: RE: redistribute ospf to igrp again
> > howdy,
> >
> > two questions:
> >
> > 1. amongst the VLSM/FLSM resolution techniques, i've
> > heard/tried several
> > options:
> >
> > secondary address
> > tunnelling
> > area X range/summary-address
> > ip summary-address eigrp
> > etc etc..
> >
> > is the touted secondary address solution the one you presented below?
> >
> > also, my reasoning behind its working:
> > note that the /30 route is in the IGRP db also on the ASBR, however,
> > when it gets redist'ed to OSPF, ospf rejects it because it
> > already sees
> > this route as connected..however a secondary address on which
> > ospf is not
> > running, would then get redist'ed into ospf, seen as an External LSA.
> > and then the summary-address would do its magic.
> >
> > in other words if we had
> > router ospf X
> > network 172.16.0.0 0.0.255.255 area X
> >
> > this solution would not work. correct?
>
> heh, buddy, too complex. It's too late in Toronto already :)
> Everything much easier:
> I meant assign sec address 172.16.0.1/24 (for example) on R2 interface
> (don't run ospf on it)
> faced to R1 (to avoid split hor issues). It's the same major net, hence
it's
> just known by IGRP without any redistribution, the same mask, the same
major
> - what else do we need ?
> Net 172.16.0.0/24 will be in R3.
>
>
> > 2. remember we once discussed this, when you and I were learning this
> > method, and i mentioned using a loopback interface for
> > 172.16.0.1/24 but
> > the idea was shot down.
>
> The same stuff as secondary. It depends what is allowed (if any ;)
>
> Dmitry
>
>
> > just want to make sure why that would be a bad idea, b/c i still like
> > using it :)
> >
> > regards,
> > Omer
> >
> > On Wed, 4 Sep 2002, Volkov, Dmitry (Toronto - BCE) wrote:
> >
> > > Hello,
> > >
> > > Since R2 is not ABR but ASBR we can not use area range command.
> > > I case if You are doing redistr between OSPF and IGRP You
> > can just put
> > > "summary-address 172.16.0.0 255.255.255.0" under OSPF process on R2
> > > It will create automatically route to Null
> > > This route will be propagated into IGRP.
> > > You can also just put secondary address (like
> > 172.16.0.1/24) on R2 interface
> > > faced to R1
> > >
> > > Dmitry
> > >
> > > > -----Original Message-----
> > > > From: elping [mailto:elpingu@acedsl.com]
> > > > Sent: Tuesday, September 03, 2002 12:37 AM
> > > > To: frank.yu@japan.bnpparibas.com
> > > > Cc: ccielab@groupstudy.com
> > > > Subject: Re: redistribute ospf to igrp again
> > > >
> > > >
> > > > do an area range command for the /30
> > > >
> > > > frank.yu@japan.bnpparibas.com wrote:
> > > >
> > > > > Group,
> > > > >
> > > > > As you can see the following diagram, R2 is ospf
> > > > ASBR and running
> > > > > igrp too.
> > > > > My question is how can R3 reach ospf area0, except
> > > > R2 advertising a
> > > > > default route to igrp?
> > > > > Is there a way for R2 to summary the ospf backbone
> > > > into 24bit route
> > > > > and redistribute it to igrp domain?
> > > > > Thanks!
> > > > >
> > > > > 172.16.0.0/30 172.16.1.0/24
> > > > > R1-------------------R2--------------------R3
> > > > > ospf area0 igrp
> > > > >
> > > > > Frank
> > > > >
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