The master/slave relationship exists ONLY during the interface states from
EXSTART (where this relationship is negotiated) until a FULL adjacency is
achieved. The master/slave relationship is then terminated for the two
routers involved.
The DR may indeed become the slave. Master is the router with highest
router ID; but consider the other two factors that influence DR
selection: timing and interface priority. It may in fact be that a router
with lower router ID was booted up first on the link and became DR; but he
would still be slave for the exchange process. This in no way affects the
functions of the DR/BDR--they are two different issues entirely.
It doesn't matter which router becomes master with respect to database
synchronization, and they don't switch roles at any point. Master will
make certain that BOTH routers have a chance to request and receive all the
information they need to achieve identical link-state databases at the end
of the process.
BTW, the master/slave relationship IS negotiated during EXSTART on
point-to-point links as well as multiaccess ones.
Little-known bit of trivia, never mentioned in the Cisco course
materials: another thing the routers examine during EXSTART is MTU
size. If the MTUs don't match on both router interfaces involved, they
will not proceed beyond EXSTART.
Pamela
At 11:08 AM 1/17/01 +0500, you wrote:
>Hi ,
>
>I agree with priscilla , but doesnt this master/slave relationship change
>after the slave had sent its dd packets to the master then the master
>becomes slave and sents the dd packets?
>
>can you send me the report of ur sniffer priscilla cause i havent yet been
>able to see this besides books
>Priscilla Oppenheimer <[EMAIL PROTECTED]> wrote in message
>[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > I don't think the master/slave business is related to DR and BDR. It has
>to
> > do with neighbor adjacency and establishing the protocol for exchanging
>the
> > link state database.
> >
> > After initializing, two neighbors establish bidirectional communication
>and
> > then enter the ExStart state. In this state, the routers establish a
> > master/slave relationship and determine the initial database description
> > (DD) sequence number.
> >
> > At first both neighbors will claim to be the master by sending an empty DD
> > packet with the Master/Slave (MS) bit set to one. The neighbor with the
> > lower Router ID will become the slave and will reply with a DD packet in
> > which the MS bit is zero and the DD sequence number is set to the master's
> > sequence number. This DD packet is the first one with actual data, that
>is,
> > LSA summaries.
> >
> > The routers then know who is the master and who is the slave and enter the
> > Exchange state where they synchronize their link state databases.
> >
> > When I first looked at all of this on a Sniffer I was pleasantly surprised
> > to discover how complicated it is! &;-) It's a little like a TCP 3-way
> > handshake.
> >
> > Priscilla
> >
> >
> > At 02:43 PM 1/16/01, Gopinath Pulyankote wrote:
> > >Hello all,
> > > Could someone explain what is master/slave relationship during DBD
> > >exchange. My understanding is that since DR is the Router with the
>highest
> > >priority value, it will always be the master. So why have this definition
>?
> > >Or is it only used on Point-to-Point links, which don't elect DR & BDR?
> > >TIA
> > >Gopinath
> > >
> > >
> > >
> > >_________________________________
> > >FAQ, list archives, and subscription info:
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> >
> >
> > ________________________
> >
> > Priscilla Oppenheimer
> > http://www.priscilla.com
> >
> > _________________________________
> > FAQ, list archives, and subscription info:
>http://www.groupstudy.com/list/cisco.html
> > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
> >
>
>
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