When was DBD(database descriptor) packets sent ?

[solemdoms5]

I know DBD packets would be exchanged when establishing adjacency after booting the router .

However after that ,Im not sure how DBD works .So

DBD packets was sent every 30 minutes ?  I mean .

When Router exchange LSDB every 30 minutes , First Do OSPF routers exchange DBD(database descriptor ) packets ?

thank you .

[Peter Paluch]

Hi John,

Without that, the other neighbor can't compare what links this peer has  to its own database in order to make an intelligent decision on what LSA  this peer could be missing.

Actually, it's the other way around: it is you (as a router) who is unable to make an intelligent decision on what LSAs you are missing. You do not force your LSAs upon your neighbor, quite the contrary: you want your neighbor's LSAs you don't have yourself.

Peter...help me out here if that's correct or not 

Don't worry - it's correct!

Best regards,

Peter

[iamkapil]

My doubts are :-

1) Can slave increase the sequence number when refreshing LSA after 30 seconds.If yes then when DR updates the same LSA to other router does it use the same sequence number shared by Slave or he will give a new sequence number.

2) In Exchange state does Slave  send LSR message  first ?

3) In Exchange state while sending LSU which sequence number slave uses. Is it the sequence number

    shared by Master 

Thanks In Advance

Kapil

[Richard Burts]

I assume that when you say " when refreshing LSA after 30 seconds" you really mean 30 minutes. Is that correct? If we are talking about the 30 minute refresh of the LSA there is no master and no slave in this activity. Each router generates a new LSA, with incremented sequence number, for each of its own locally generated LSAs. There is not any aspect of master or of slave in this. The master slave relationship is only used when the adjacency is initially being formed. After the adjacency is formed there is no more master/slave.

[iamkapil]

Thanks for the reply. By mistake i wrote 30 secs. Sorry for that.

One more doubt:-

When a Router is both ABR and ASBR does it send LSA 4 in case of 1) Standard Area and 2) NSSA AREA

[Richard Burts]

Kapil

LSA type 4 are generated for both standard and NSSA areas.

[Cristian Matei]

Hi,

@Richard Burts An ABR will generate a Type4 LSA (one for each ASBR it knows about) into a destination area, only if it forwards a Type5 LSA into that area. As NSSA means there are no Type5 LSA's, thus the ABR will never forward a Type5 LSA in that area, it means the ABR will never generate a Type4 LSA in the NSSA area.

Regards,

Cristian Matei.

[Richard Burts]

The source that I consulted in preparing my response clearly stated that type 4 LSA was used in both standard and NSSA areas. But I find the logic from @Cristian Matei to be compelling and to show a mistake in the source that I consulted and therefore a mistake in my response. I thank you for the correction.

[Cristian Matei]

Hi,

   @Richard Burts I appreciate you coming back on this, as it gives me the opportunity to thank you and respect you for the attitude you're showing, caring more about making sure we help each other to understand how things work so that everyone can benefit, rather than not admitting that we all can be wrong sometimes, no matter why. If you would have not replied, someone else reading the thread, would have left with more questions, instead of an answer.

              To double that, I never correct someone, this s not my scope, by far. I just say how things work, but most importantly why, as this is one of the keys for gaining knowledge and keeping it long-term. I've been struggling for years to learn how to learn so i never have to re-learn or have the feeling of actually not knowing it, or forgetting it. At some point, i made it, so that whatever i learn, i do it only once, and i want to share this approach.

PS:  Don't trust the Internet :) 

Regards,

Cristian Matei.

[Richard Burts]

@Cristian Matei I appreciate your contribution to the community and your attitude about it. One of the great advantages of this community is the cooperative attitude that is exhibited. We have multiple people looking at discussions and sharing their insight. And it provides opportunity when we occasionally make a mistake (as we all do from time to time) for someone to provide the clarification. We all benefit in the end.