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ospf dr election and adjok? event

HI all,

someone knows in which circumstances the adjok? event is invoked?

The rfc 2328 ospf says :

If the above calculations have caused the identity of either
            the Designated Router or Backup Designated Router to change,
            the set of adjacencies associated with this interface will
            need to be modified.  Some adjacencies may need to be
            formed, and others may need to be broken.  To accomplish
            this, invoke the event AdjOK?  on all neighbors whose state
            is at least 2-Way.  This will cause their eligibility for
            adjacency to be reexamined (see Sections 10.3 and 10.4).

I have noted tha in some cases, even if the election of DR and BDR is estabilished , when a new adjacency is formed (with a potentially BDR or DR) , an event of Adjok? is invoked from the two-way adjacent router:

the adjiacent 2-way  send  (or receive?) an AdjOK to 10.10.1.1 , and the DR election restart:

Jul 21 06:50:17: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.1.1 on FastEthernet1/0/

0 from INIT to 2WAY, 2-Way Received

Jul 21 06:50:17: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.1.1 on FastEthernet1/0/

0 from 2WAY to EXSTART, AdjOK?

In other cases this event is not invoked:

Jul 21 07:37:04: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.1.1 on FastEthernet1/0/

0 from DOWN to INIT, Received Hello

Jul 21 07:37:09: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.1.1 on FastEthernet1/0/

0 from INIT to 2WAY, 2-Way Received

Thanks

Everyone's tags (1)
2 REPLIES
Hall of Fame Super Silver

Re: ospf dr election and adjok? event

Hello Federica,

in the second log example that you have provided the initiial OSPF neighbor state is down so the message is not generated as there is no need to reconsider adjacencies on a new link.

In first example the OSPF neighbor state initial state is init

So we could say that if the neighbor state regresses to down the list of adjacencies is cleared and the link is considered a new link.

Actually only a new BDR election can be triggered when a new router comes online no one can preempt over current DR in segment.

As a result of this in many network segments the OSPF DR is likely the device with the highest uptime not the one with the highest priority/router-id.

This could explain the different behaviour that you see (for example if you have played with OSPF priority on link).

But this would too easy and you wouldnt have written here!

Hope to help

Giuseppe

New Member

Re: ospf dr election and adjok? event

Thanks Giuseppe for your suggestion...

So:

If a new adjacency from a DOWN state comes, that's no need to recalculate the new BDR/DR , even if the new routers has priority/RID higher than the existing BDR/DR . SO no new election is computed.  This is the acquainted behavoiur ...

BUT if a neighbor (with the highest priority/RID)  with state INIT comes (not passing to down state), the neighboring in two-way state,invokes the adjok? to recalculate the new BDR/DR..?

If it seems so,  I've to understand why  10.10.1.1 is passed from FULL (he was the DR/BDR) to INIT,

Jul 21 06:49:47: %OSPF-5-ADJCHG: Process 1, Nbr 10.10.1.1 on FastEthernet1/0/

0 from FULL to INIT, 1-Way

This is because the hello packet the neighbor has receveid from  10.10.1.1  was without his router id .. it's very strange , I suspect a bug on the version of 10.10.1.1.. (12.0.S15..)..

Let me know your opinion...

Federica

ANYWAY In rfc 2328 (pages 93-94)  I don't see differences in the passage from any state -to DOWN and from FULL To INIT,

"""  State(s):  Any state                Event:  LLDown            New state:  Down               Action:  The Link state retransmission list, Database summary                      list and Link state request list are cleared of                      LSAs.  Also, the Inactivity Timer is disabled.                            State(s):  2-Way or greater                Event:  1-WayReceived            New state:  Init               Action:  The Link state retransmission list, Database summary                      list and Link state request list are cleared of                      LSAs."""""

The database is cleared in both case....  So the problem is why there is an adjok? invoke....

Federica

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