From: Richard Dumoulin (richard.dumoulin@vanco.es)
Date: Mon Apr 12 2004 - 10:27:27 GMT-3
Peter, I think the theory behind the concept is not so complicated. For me
it's more complicated to remember which config technique do what in this
case. The forwarding address idea was introduced in order to avoid extra
hops.
Suppose 2 routers (A and B) connected through a multiaccess link. Both are
running ospf and a third one (C) is connected to the same link. Only router
A is exchanging external routes with router C (BGP). Then A redistributes
the external routes into the ospf domain (to B). Thanks to the forwarding
address concept, router B will be able to directly send his packets to C
instead of having to do an extra hop via A,
Regards
--Richard
-----Original Message-----
From: Peter van Oene [mailto:pvo@usermail.com]
Sent: lunes, 12 de abril de 2004 15:06
To: Richard Dumoulin; ccielab@groupstudy.com
Subject: RE: advertise ospf as 192.168.1.1 /29 0.0.0.0 area 0 and
At 03:32 AM 4/12/2004, Richard Dumoulin wrote:
>Hi Peter, I am not sure I understand your question. I only know that
>the concept of forwarding address was reflected in the ios at some
>point.
Well, I was hoping we'd get the theoretical reason for this issue posted to
the list for those interested in understanding the technology, vs knowing
what commands to type to avoid a particular pitfall . I worked a pretty
good sizes EIGRP / OSPF migration that ran into a lot of forwarding address
inter area routing issues which are well rooted in theory, but arcane to
some degree.
>-----Original Message-----
>From: Peter van Oene [mailto:pvo@usermail.com]
>Sent: lunes, 12 de abril de 2004 4:54
>To: ccielab@groupstudy.com
>Subject: RE: advertise ospf as 192.168.1.1 /29 0.0.0.0 area 0 and
>
>
>At 01:51 PM 4/11/2004, Richard Dumoulin wrote:
> >Allan,
> >
> > I would use 0.0.0.0 to go faster on the exam but I would be careful
> >when configuring asbr's as mentioned by Serran on multiaccess
> >interfaces.
> >
> >I have just found a case where using the wild card mask instead of
> >0.0.0.0 was not appropriate. Redistribution was being done on the
> >asbr but the only way to have full connectivity was to have the asbr
> >advertise his own address (forwarding address) for the redistibuted
> >routes,
>
>Do you know why this is? Ie, what is the issue at play here?
>
>
>
>
> >Regards
> >
> >--Richard
> >
> >
> >-----Original Message-----
> >From: Scott Morris [mailto:swm@emanon.com]
> >Sent: domingo, 11 de abril de 2004 15:30
> >To: 'Allan Wells'; ccielab@groupstudy.com
> >Subject: RE: advertise ospf as 192.168.1.1 /29 0.0.0.0 area 0 and not
> >0.0.0.7
> >
> >
> >You need to understand the behavior of the "network" command with IGP
> >protocols (BGP is different, in a lot of things!).
> >
> >The network command does not specifically say which networks to
> >advertise. Instead, it indicates to the router which networks will
> >participate in the routing protocol. If the IP address of an
> >interface falls within that range, then it is 'tagged' as
> >participating in the routing protocol. THEN the actual network that
> >the interface has will be brought in.
> >
> >For example, if you have:
> >
> >E0/0 = 10.0.0.1/24
> >S0/0 = 10.0.1.1/24
> >S0/1 = 10.0.2.1/24
> >E1/0 = 10.0.3.1/24
> >
> >You can say:
> >
> >Network 10.0.0.1 0.0.0.0 area 0 and this will only match the e0/0
> >Network 10.0.0.0 0.0.0.255 area 0 and only e0/0 will fall within that
> >range Network 10.0.0.0 0.0.0.3 area 0 and still only e0/0 will fall
> >within that range Network 10.0.0.0 0.0.1.255 area 0 and both e0/0 and
> >s0/0 will fall in here Network 10.0.0.0 0.0.3.255 area 0 and all four
> >interfaces will participate in ospf Network 0.0.0.0 255.255.255.255
> >area 0 and every single interface on the router will participate in
> >ospf
> >
> >There are many ways to do it, but the only thing you are indicating
> >to the router is which interfaces participate in the routing
> >protocol. The networks advertised comes as a later step within ospf.
> >
> >HTH,
> >
> >
> >Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
> >CISSP, JNCIS, et al. IPExpert CCIE Program Manager IPExpert Sr.
> >Technical Instructor swm@emanon.com/smorris@ipexpert.net
> >http://www.ipexpert.net
> >
> >
> >
> >-----Original Message-----
> >From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> >Of Allan Wells
> >Sent: Sunday, April 11, 2004 5:34 AM
> >To: ccielab@groupstudy.com
> >Subject: advertise ospf as 192.168.1.1 /29 0.0.0.0 area 0 and not
> >0.0.0.7
> >
> >Hi,
> >
> >
> >
> >I have been doing some labs and looking at all the solutions.
> >
> >
> >
> >Why is it some labs setup OSPF to use wildcard mask 0.0.0.0 with say
> >/29 multipoint hub and spoke network
> >
> >As apposed to to using 0.0.0.7 mask also I tried this config with
> >eigrp and theirs no problem their either what is the better way and
> >why.
> >
> >
> >
> >I always was under the impression we need to advertise the mask of
> >the network in the above example 0.0.0.7 obviously not.
> >
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