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
>
>
>
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