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Re: Doubt on sending hello packets on NBMA networks

Kishore Rao wrote:

Possible scenarios

- Timing difference between dynamically changing the eligibility
configuration/setting interface priority Vs sending of a Hello.


Yup - You don't really even need timing differences - any event which causes a new DR/BDR to
be elected would cause the new DR/BDR to start polling non-eligible neighbors that
hadn't heard from them before.

- Mismatch in configuration between interface priority of a router and its
eligibility configuration on other routers.


Yes.

Kishore




hi Acee,

yeah i got it. but just for the sake of curiosity. can you give me
some more scenarious where this can happen?

Thanks
Srini

-----Original Message-----
From: Acee Lindem [mailto:acee at CISCO.COM]
Sent: Monday, May 09, 2005 6:40 PM
To: OSPF at PEACH.EASE.LSOFT.COM
Subject: Re: Doubt on sending hello packets on NBMA networks


Srinivasa J Ragavan wrote:



hi All,

I am a newbie to OSPF.
can anyone help me out.
this is with reference to the rfc 2328 sec. 9.5.1 whcih says
"  If the router is eligible to become Designated Router, it
          must periodically send Hello Packets to all neighbors that
          are also eligible."

but immediately in the next paragraph it says

" It must also send an Hello Packet in reply to an
          Hello Packet received from any eligible neighbor (other than
          the current Designated Router and Backup Designated Router)"

how can a non eligible router get a hello from a eligibe router if the
eligible router is not going to send(tatz what the first argument says)




Srini,
In the NBMA case (which is described in section 9.5.1), a non-eligible
router
needs to reply to any eligible neighbor since it may not know the current
DR/BDR. There are a number of scenarios where this can happen including
the case where the non-eligible neighbor first comes up and receives a
hello poll
from the current DR/DBR. The non-eligible neighbor needs to establish
bi-directional connectivity with the potential DR/BDR in order for its
local DR/BDR election to work.

Hope this helps,
Acee




Am i missing something here??

thanks
Srini





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