From: Howard C. Berkowitz (hcb@gettcomm.com)
Date: Sun Dec 08 2002 - 13:57:47 GMT-3
At 7:24 PM -0500 12/7/02, OhioHondo wrote:
>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?
I can't answer completely because I also need to know your addressing
structure. Are all these PVCs in the same subnet?
>
>1 - A pvc between two non-DR/BDR routers fail.
Now I am confused. Is the full mesh among all the OSPF speakers
regardless of subnet?
NBMA generally assumes hub-and-spoke. Direct links between spokes
aren't really part of the paradigm. How could this link be in the
same subnet as the links to the DR?
>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 the BDR stops hearing the DR, it should promote itself to DR. Of
course, if the DR is still active, both the original DR and the BDR
may both think they are DR. In a true broadcast environment, this
shouldn't be a problem, because the updates are being sent the the
multicast group AllDRouters. Again, I'd need to see your addressing
as well as your topology.
>
>
>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.
Again, I am confused -- it sounds like you are describing something
that might have multiple subnets.
.
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