From: OhioHondo (ohiohondo@columbus.rr.com)
Date: Sat Dec 07 2002 - 21:24:47 GMT-3
Everybody
I always assumed that the full mesh environment would "self heal" with the
loss of a single pvc in the mesh. I found this not to be the case. I tested
two instances using both OSPF network types "broadcast" and "non-broadcast".
If the findings below are true the advantages of having a full mesh only
apply to when an entire sync interface goes down?
1 - A pvc between two non-DR/BDR routers fail.
When this occurs traffic between the two non-DR/BDR routers is non-existant
even though the IP routing tables of the routers indicate that there is a
path. The reason seems to be that the non-DR/BDR routers receive their view
of the network from LSA's provided by the DR. The DR shows both of the
non-DR/BDR routers as active in a network, LSA type 2 update. The non-DR/BDR
routers build IP routing table entries showing the next-hop to one another
as direct to the others sync interface on the frame relay. That pvc is down
so no traffic flows between them.
2 - The pvc between the DR and the BDR fails.
When this happens the BDR may keeps its' neighbor relationship with the
non-DR/BDR routers and continue to receive updates from them OR if one of
the non-DR/BDR routers becomes BDR then the old-BDR router is totally
divorced from the network. In any case the BDR loses all connectivity with
the DR and therefor loses DR routes in its' routing table and doesn't
receive updates from the DR. Bad, bad, bad.
If an entire sync link is lost instead of a single pvc, the remaining
routers are still in a full mesh. They act accordingly, electing a new DR
and BDR if necessary. They do not reflect IP routes as accessible when they
are not -- as in the first instance above.
.
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