RE: ospf point-to-multipoint

From: Brian Dennis (brian@labforge.com)
Date: Wed May 21 2003 - 20:24:32 GMT-3


I'll skip the first question and let you figure that one out ;-) I would
highly recommend you pick up a book or read the RFC on OSPF.

As far as the second one is concerned it's because the RFC said so ;-)

<RFC2328>
  12.4.1.4. Describing Point-to-MultiPoint interfaces

   For operational Point-to-MultiPoint interfaces, one or
   more link descriptions are added to the router-LSA as
   follows:

   o A single Type 3 link (stub network) is added with
       Link ID set to the router's own IP interface
       address, Link Data set to the mask 0xffffffff
      (indicating a host route), and cost set to 0.
</RFC2328>

The reason is to ensure that every spoke can reach every other spoke.
This is needed for a physical or multipoint subinterface that does not
have mappings from spoke to spoke. A point-to-point subinterface does
not need the /32 route.

Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)

-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
netchild ccie
Sent: Wednesday, May 21, 2003 3:00 PM
To: ccielab@groupstudy.com
Subject: ospf point-to-multipoint

Dear Group,

I have three routers connected as hub-spoke topology. I'm runing ospf on

frame relay as multipoint interface on the hub router and normal
physical
interface on the spoke routers.

I configured ospf as point-to-multipoint network. I have two questions
regarding this setup.

(1) Why I don't need to disable split-horizen on the hub serial
interface ?
I need to do that when I configured RIP or EIGRP for the same setup.

(2) What is the use of /32 route that ospf inject to the route-table
when I
use point-to-multipoint network since the next-hop is the IP address of
the
hub router.

Regards,
NetChild,



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