Hey, Michael,
Here I go again... Chuck, correct if I say anything wrong!!!:) I am
quoting this from memory...
OSPF modifies its behavior based on what it defaults to on an interface.
For example, OSPF will default point to point over a point to point link
(i.e. HDLC), and will not elect a DR and the two routers on the link
will become neighbors. Hello's are multicasted between each router.
LSA's are unicasted.
You, as the human network engineer, can modify and tell OSPF how it
should behave. For example, if you had two routers connected via their
ethernet (a broadcast network) interface, you could tell OSPF that the
network was point to point; it would not elect a DR as it normally would
on a broadcast network.
When you tell OSPF that the network is Point to Multipoint, it will
treat the network as a collection of point to point links; one of the
routers will be the hub (it has connectivity to all other routers), all
other routers will be spokes. The spokes can talk to the hub and vice
versa, but not each other. Again, as on a point to point network, no DR
is elected, multicasting is supported by default.
When you tell OSPF that the network is nonbroadcast, you are telling it
that it can not multicast. Since it can not multicast its hello's, the
routers on the NBMA network will not become neighbors. You as the
engineer must execute the neighbor command, and tell the routers who
their neighbors are. A DR is elected on a nonbroadcast, and the
priority could become important, depending on the amount of meshing you
have.
-----Original Message-----
From: [EMAIL PROTECTED] ("Yonker Bonk")
[mailto:[EMAIL PROTECTED]]
Posted At: Friday, June 16, 2000 11:20 PM
Posted To: cisco
Conversation: Difference between OSPF on NBMA Broadcast and
Point-to-Multipoint?
Subject: Difference between OSPF on NBMA Broadcast and
Point-to-Multipoint?
Could anyone clarify for me the difference between OSPF on NBMA
Broadcast
and Point-to-Multipoint? The configuration looks the same to me. I'm
using
the All-in-One CCIE Study Guide as reference, lab 37 or something. I
know
that with P-to-M, that no DR is elected and whatnot, but could you give
me
something more concrete? What is real world difference? When would you
ever
run an NBMA network as broadcast? To cut down on configuration?
Thanks.
Michael
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