From: Yves Fauser (Yves@xxxxxxxxx)
Date: Sun Aug 12 2001 - 11:10:34 GMT-3
Bryan,
I think you are right, we may both have some kind of a IOS Version trouble,
but more likely it will not work on Point-to-Multipoint or Physical FR
interfaces in any Version. I saw a scenario that worked with isis on FR PtM
interfaces (in ECP1), but this scenario had a major difference, one spoke was
a level-1 and the other spoke was a level-2 router of another Area. I just
tried it out again, and it works in my home lab. After reading some more of
Doyle VolI I think I know why (please correct me if I'm wrong guys).
Doyle, Page 607 :
"Unlike OSPF ISIS router attached to a broadcast multi-access network
establishes adjacencies with all of its neighbors on the network, not just the
DR. Each Router multicasts its LSP's to all of his neighbors, and the DR uses
a system of PDU's called Sequence number PDU's (SNP) to ensure that flooding
is reliable."
Doyle, Page 608 :
"As the L1 and L2 priorities suggest, separate DR's are elected on a network
for level 1 and level 2."
In OSPF the DR is like a "route reflector" in BGP. In ISIS the DR is only used
to control the Exchange of LSP's between the neighbors. Since the ISIS and
OSPF multicast/unicast will have a TTL of 1, they will die on the FR HUB. In
OSPF, when the DR is the HUB, there is no need for the LSA to take 2 hops
(Reflection). In ISIS it has to take 2 hops to work, and this is not possible
since the TTL is 1. If you have 2 Spokes, one is a level-1 and the other is a
level-2 it works, since two separate adjacencies are build. If both are
level-1 or both are level-2, it will not work since the DR concept of ISIS has
no knowledge of NBMA Networks. If you have 3 spokes you can't use this trick
anymore since you must have either 2 level-1 1 level-2 routers ore the
opposite.
Any comments are more than welcome,
Good luck, Yves
"Cox, Bryan" wrote:
> Group,
>
> I have come to the conclusion that ISIS won't run in a frame-relay
> environment with physical or multipoint interfaces without a full-mesh.
> Even with "frame map clns <dlci> broadcast" on the spokes and hub I never
> see the ISIS hellos being received at a spoke from another spoke. Thus no
> adjacency is formed between the spokes.
>
> In a full mesh I see the appropriate hellos between all points in the
> frame-relay network. IS-IS forms adjacencies and all routes are installed
> in the table.
>
> Does anybody have any working configs for a hub and spoke environment with
> point-to-multipoint or physical interfaces that they can post that say
> otherswise? Or am I on the right track?
>
> Thanks,
>
> Bryan
> San Jose October 25th
> **Please read:http://www.groupstudy.com/list/posting.html
**Please read:http://www.groupstudy.com/list/posting.html
This archive was generated by hypermail 2.1.4 : Thu Jun 13 2002 - 10:31:49 GMT-3