what does logic have to do with it? the protocol behaves in a particular
manner. one can devise all kinds of bizarre scenarios that reveal situations
that make no sense.
if I read the scenario below correctly, you have R1, R3, R4, and R5 on a
broadcast network? or just R1 and R3? Actually, it should not matter.
what should happen, when the R1 ethernet connection is restored, is that R3
and R1 are both DR's, and that a new election takes place. This can happen
when the network first comes up, by the way. yes it may seem illogical, but
in fact, things are happening the way they are supposed to happen. what
other method of operation would make more sense?
In general, broadcast networks are deemed far more reliable than other kinds
of links. the procedure is designed more to account for hardware failure
than link failure, I would think.
Chuck
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]]
Sent: Monday, September 17, 2001 8:05 AM
To: [EMAIL PROTECTED]
Subject: RE: Need clarification on BDR promotion to DR [7:20163]
I understand this principle, but there is no logic with the scenario
On convergence as outlined in BSCN as follows....
R2
R5 ---- R4 ---- R3 ------------R1
Here, R2 has serial links to R1 and R3. Let's say R3=DR and R1=BDR.
BSCN states that if the Ethernet link is disconnected between
R1 and R3, then R1 would sense that the DR went "down" and proceed
To promoting itself as the new DR.
I must admit I haven't tested this exact scenario yet, but I've seen
Similar cases where the two routers in question would get stuck in
Exstart/Exchange forever, and this particular behavior I've succeeded
In reproducing on a test lab.
Elmer
-----Original Message-----
From: Peter Van Oene [mailto:[EMAIL PROTECTED]]
Sent: Monday, September 17, 2001 9:42 AM
To: [EMAIL PROTECTED]
Subject: Re: Need clarification on BDR promotion to DR [7:20163]
So far as the multiaccess segment is concerned, when you remove the DR from
the segment, the DR is down. The only way a DR can do its job is if it has
access to the segment in question. In this case, promoting the BDR makes
sense since the BDR is the only other router on the segment which has
adjacencies with all other routers and has sufficient information on where
the DR left off to be able to take over quickly. When the old DR comes
back, it will not become the BDR unless it is the only other router eligible
on the segment since a BDR election would have already taken place to
replace the promoted BDR.
Does that help?
Pete
*********** REPLY SEPARATOR ***********
On 9/17/2001 at 8:55 AM Elmer Deloso wrote:
>Hi, all.
>I'm trying to understand the PURPOSE and LOGIC behind OSPF BDR
>Promotion to DR. Let's say R1 is DR and R2 is BDR connected via Ethernet
>Link. If I disconnect the cable, this would mean the BDR will promote
>itself
>To DR status, even though the DR never went "down". So when I reconnect the
>Link the DR will just "abdicate" the role? I just don't see the logic here.
>So now the DR will become the BDR, and if we repeat the process of
>disconnecting
>The link, the original scenario is restored. I've read OSPF on CCO and
>Doyle
>but
>Have not come across the explanation of why OSPF was designed to behave
>this
>Way. Any enlightenment on this is welcome.
>
>Elmer
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=20202&t=20163
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