tree 7082972f63b091f0e8bcbbf9a285fe10e5136a8d
parent 4b4bda9bb1913579bd54667f62fafe58e2746478
author Lu Feng <lu.feng@6wind.com> 1392970275 +0000
committer David Lamparter <equinox@opensourcerouting.org> 1400078788 +0200

ospfd: check the LS-Ack's recentness instead of only comparing the #seq

ISSUE:

RTA(DR)-----(BackupDR)RTB

RTA advertises a new LSA to RTB, and then flushes the LSA (with setting
the age of the LSA to MaxAge) within 1 second. Then the LSA is deleted
from RTA, while it still exists on RTB with non-MaxAge and can not be
flushed any more.

FIX:

The reason can be explained in below:

a) RTA -- new LSA, #seq=1 --> RTB (RTB will send the delayed Ack in 1s)
b) RTA -- MaxAge LSA, #seq=1 --> RTB (RTB discards it for the MIN_LS_ARRIVAL)
c) RTA <-- Ack for the new LSA, #seq=1 -- RTB (RTA accepts it)

In the step c), ospf_ls_ack() compares the #seq of the entry in the LS-Ack
with that of local MaxAge LSA. The #seq of the two entries are same. So
the Ack is accepted and the LSA is removed from the retransmit-list (while
it should not).

In RFC2328, section  13.7.  Receiving link state acknowledgments:

o   If the acknowledgment is for the same instance that is  <==
    contained on the list, remove the item from the list and
    examine the next acknowledgment.  Otherwise:

where "same instance" does not mean the same #seq. We must call
ospf_lsa_more_recent() to check whether the two instances are same.

Signed-off-by: Feng Lu <lu.feng@6wind.com>
Signed-off-by: Christian Franke <chris@opensourcerouting.org>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>