Re: [OSPF] LSA Data Base Exchange Between the Master and the Slave

Hi Biswajit,

On Jul 3, 2013, at 6:35 AM, Biswajit Sadhu wrote:

Hi All,

I have a query in the OSPF Design of LSA Data Base Exchange.

In data base exchange process if the master has smaller database the the slave and the master sends the More bit as zero in its DB packet  then the slave should also set the M bit to 0 in reply to the master's DB packet with the same sequence number ?

No. The slave should continue to set the M bit until it has sent its entire database. The master should continue to poll the slave with increasing sequence numbers until the slave has completed exchanging its entire database and cleared the M bit. Excerpt from RFC 2328:

        This sending and receiving of Database Description packets is
        called the "Database Exchange Process".  During this process,
        the two routers form a master/slave relationship.  Each Database
        Description Packet has a sequence number.  Database Description
        Packets sent by the master (polls) are acknowledged by the slave
        through echoing of the sequence number.  Both polls and their
        responses contain summaries of link state data.  The master is
        the only one allowed to retransmit Database Description Packets.
        It does so only at fixed intervals, the length of which is the
        configured per-interface constant RxmtInterval.

Each Database Description contains an indication that there are
more packets to follow --- the M-bit. The Database Exchange
Process is over when a router has received and sent Database
Description Packets with the M-bit off.

Read RFC 2328 sections 10.6 and 10.8 and it should be clear. The actions of the database exchange master and slave are described in detail.

Hope this Helps,
Acee

 Should the data base exchange stop after that. what if the slave had more lsa's to send to the Master?

What about the vice-versa case where Master has a large Data base to exchange then the Slave  ?

   As per page 101 .rfc 2328 i am quoting few lines for the same RFC

    http://tools.ietf.org/html/rfc2328

        Master
            Increments the DD sequence number in the neighbor data
            structure.  If the router has already sent its entire
            sequence of Database Description Packets, and the just
            accepted packet has the more bit (M) set to 0, the neighbor
            event ExchangeDone is generated.  Otherwise, it should send
            a new Database Description to the slave.

        Slave
            Sets the DD sequence number in the neighbor data structure
            to the DD sequence number appearing in the received packet.
            The slave must send a Database Description Packet in reply.
            If the received packet has the more bit (M) set to 0, and
            the packet to be sent by the slave will also have the M-bit
            set to 0, the neighbor event ExchangeDone is generated.
            Note that the slave always generates this event before the
            master.

 Best Regards,

Biswajit Sadhu

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