03-30-2011 02:13 PM - edited 03-04-2019 11:55 AM
Hi Everybody,
The best definition that I have found for OSPF exchange state is the following:
In this state, the routers exchange DBD packets, which describe their entire link-state database. The routers also send link-state request packets, which request more recent link-state advertisements (LSA) from neighbors.
I am not sure about this definition because I do not see any information about DBD packets when I am looking at OSPF DB Descr. packets with WireShark.
Can somebody also confirm me that this exchange state will be done with every neighbor in a multi-access segment.
Thanks for your help
Stéphane
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03-30-2011 09:44 PM
Hi Stephane,
If you focus between two routers only, you will see that the first DD packets exchanged are used to establish master/slave relationship. Then the following ones will contain the LSA header. I noticed there is a last empty DD exchange but not sure about the reason of this one. I saw the M bit is set during the 2nd exchange which explains the 3rd exchange but don't know why.
For DR/BDR election to occur, all routers on the segment must have reach 2-ways or higher state so yes you can expect DD exchange between everyone until DR/BDR election is done.
Please check RFC 2328 for all the dirty details ;-)
HTH
Laurent.
03-30-2011 07:12 PM
Stephane
Actually a router does not do the full exchange of database with every neighbor on a multiaccess network. It will do the full exchange with the DR of the segment and with the BDR ( if present ) but not with every neighbor.
HTH
Rick
Sent from Cisco Technical Support iPhone App
03-30-2011 09:44 PM
Hi Stephane,
If you focus between two routers only, you will see that the first DD packets exchanged are used to establish master/slave relationship. Then the following ones will contain the LSA header. I noticed there is a last empty DD exchange but not sure about the reason of this one. I saw the M bit is set during the 2nd exchange which explains the 3rd exchange but don't know why.
For DR/BDR election to occur, all routers on the segment must have reach 2-ways or higher state so yes you can expect DD exchange between everyone until DR/BDR election is done.
Please check RFC 2328 for all the dirty details ;-)
HTH
Laurent.
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