Curtis,

Curtis Call wrote:

> I couldn't find this answer in the archives. I suspect that I am missing a
> step somewhere so I'd appreciate any clarification someone could offer:
>
> On a broadcast network, Router A is the DR, Router B is the BDR, and Router C
> and D are DRother routers. Router A goes offline, but it is still within the
> DeadInterval so the other routers are not aware of this yet. Router C floods
> an update packet to AllDrouters. Router B receives this packet but does not
> acknowledge it because it is the BDR and it wasn't flooded out the receiving
> interface (13.5) At this point Router B also adds the LSA to the
> retransmission list for router A and D (but not neighbor C since it sourced
> the packet) but it does not flood the packet onto the interface since it is
> the BDR (13.3). Now, since Router A is down and D will not receive the packet
> or acknowledge it Router B will end up sending a retransmission to Router D as
> a unicast with the LSA. However, the problem I see is that at no point will
> Router B acknowledge the receipt of the LSA to Router C, so Router C will end
> up retransmitting the LSA to Router B. Am I missing something somewhere?
>
> Thanks.

when there is no ack from a neighbor we retransmit the LSA after RxmtInterval time
and unicast it, so when Router C send an update while DR is down since there would
be no Ack from DR ( even BDR is waiting for DR update back on the same Interface )
Router C end up unicasting this to both DR and BDR.
but DR notice that this is a duplicate LSA and per RFC we send imediately a
unicast Ack.

Sina

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