I stand corrected, in that Frame-Relay can be more than just a NBMA, which
in turns leads to the difference to whether you need an adjacency or a
DR/BDR. I should have said "By default, a Frame Relay network provides NBMA
connectivity between remote sites" (pg. 119 CiscoPress BSCN).
Sometimes I tend to throw things out there without double-checking them.
Since I have no one to learn from or to teach here in my current position,
that's what I tend to use groupstudy for. Thanks for the correction to my
post. Now I have to go look up some information on Howard's post about
Demand Circuits...
Joey
-----Original Message-----
From: Brian Lodwick [mailto:[EMAIL PROTECTED]]
Sent: Wednesday, January 31, 2001 12:35 PM
To: [EMAIL PROTECTED]; [EMAIL PROTECTED]
Subject: RE: DR Election
Joey,
I am really glad this message is out there, because I was going to write one
confirming my findings with the group. I believe on one part you are wrong
in your explaination. I have read and read and the big question is:
What the heck is the difference between NMBA and point-to-multipoint?
You said there are 3 network types well, actually there are 4 types.
point-to-point
point-to-multipoint
broadcast
NBMA
So what is the difference? I conclude the difference is how you want
adjacencies created.
As you noted Ethernet is a good example of Broadcast. ~I agree
You note a good example of NMBA is Frame-Relay. ~I don't fully agree
Frame-relay could be a point-to-point connection, but never a Broadcast
(same with ATM, and X.25)since it is not possible to broadcast on these link
technologies.
Point-to-point is fairly easy to figure out. Two routers connected only to
each other.
Point-to-multipoint is a router with more than one connection off of an
interface. This is also the definition of a NBMA, the difference is in
point-to-multipoint treats each link as a point-to-point link and no DR/BDR
is elected and adjacencies are created just like point-to-point links. On a
NBMA network DR/BDR is elected and when routing information is sent to and
from the DR/BDR with unicast packets.
I conclude the difference is administratively decided and should be based
upon the way you want adjacencies built, and if you would benefit by this
decrease in overhead.
>>>Brian
>From: "Fowler, Joey" <[EMAIL PROTECTED]>
>Reply-To: "Fowler, Joey" <[EMAIL PROTECTED]>
>To: [EMAIL PROTECTED]
>Subject: RE: DR Election
>Date: Wed, 31 Jan 2001 10:44:40 -0500
>
>There are three main types on environments (I hope)
>
>Broadcast
>Point-to-Point
>NBMA (Non-Broadcast Multi-Access)
>
>Point to Point would not be a multi-access segment. The other two would. An
>Example of Broadcast is Ethernet, while an example of NBMA would be
>Frame-Relay. Following this logic ' DR and BDR concepts ' would not have to
>be broadcast, only multi-access. Point to point creates an adjacency
>instead
>of using DR's and BDR's.
>
>I hope the diagram below turns out, but the first one is point to point, so
>information is exchanged directly, however in a multi-access environment
>both other routers only exchange information with the DR so as not to have
>to have an adjacency with every single router.
>
>X-------X
>
> ----O
>X-|
> ----O
>
>If OSPF worked that way and you had 10 routers connected via Ethernet, each
>would each have to exchange information with the other 9. That would create
>45 adjacency's. Way to much traffic would have to exchanged. With those
>same
>10 Routers using OSPF DR and BDR concepts, you could have 1 Router with 10
>"Adjacency's" total. Much less routing traffic. I hope I haven't muddled
>things to much.
>
>Joey
>
--snipped By me!
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