Re: OSPF DR/BDR

It is true, there is replication when a ospf router sends a LSU to
224.0.0.6, which is then subsequently re-flooded by the DR to 224.0.0.5.
Interestingly, IS-IS doesn't have this issue, since routers simply
multicast LSPs onto the LAN and all other routers accept them, the DIS only
sends CSNPs on a regular interval to insure database synchronization. The
DIS would only re-flood an LSP if another router was missing or had an
outdated LSP listed in the CSNP, and requested it via PSNP.

I think one situation that makes OSPFs implementation more efficient is
when you have A LOT of updates being flooded onto a LAN segment by many
different routers. The DR could then send batch updates onto the LAN (as
controlled by the flood pacing timer), which theoretically saves cpu cycles
on other routers since they would be processing fewer LSUs.

-YuriB

On Thu, Mar 21, 2013 at 1:05 AM, shiran guez <shiranp3_at_gmail.com> wrote:

> Think of the difference between having DR/BDR on a LAN/NBMA to not as
> the difference of doing a star topology vs doing a full mash which is
> more expensive?! (the answer is full mash).
>
>
>
> On Thu, Mar 21, 2013 at 8:46 AM, Mohammad Mousa <mohd-mousa_at_hotmail.com>
> wrote:
> > Hello Folks,
> >
> > Appreciate if someone could clear up this point for me.While I'm
> reviewing the OSPF, I noticed this issue.
> > In the ospf Net-type (broadcast,Non-broadcast). The advantages of using
> the DR/BDR are:
> >
> > 1-Minimize the adjacencies.
> > 2-Minimize LSA replication.
> >
> > Suppose we have ethernet LAN segment between four routers R1,R2,R3,R4.
> R1 is DR, R2 is BDR. I know drothers will stay in the 2-way states. When R3
> generate LSU it will go for 224.0.0.6 and then DR will replicate this to
> all multicast ospf routers 224.0.0.5. My question is suppose we don't have
> the DR. R3 will generate the LSU to 224.0.0.5 (All routers on that LAN
> segment). So using DR IS NOT giving me the benefit by reducing the LSA
> replication on the segment. Am I correct? Any thought will be highly
> appreciated!
> >
> > Thanks in advance
> > --
> > Mohammad
> > CCIE #36990
> >
> >
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> >
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> >
>
>
>
> --
> Shiran Guez
> MCSE CCNP NCE1 JNCIA-ENT JNCIS-ENT JNCIP-ENT CCIE #20572
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Received on Thu Mar 21 2013 - 02:03:03 ART