Without knowing too much more information I would try this…

* Restart node each node in turn, watch the logs to see what it says about the other. 
* If that restart did not fix it, try using the  Dcassandra.load_ring_state=false JVM option when starting the node. That will tell it to ignore it's stored ring view and use what gossip is telling it. Add it as a new line at the bottom of cassandra-env.sh. 

If it's still failing watch the logs and see what it says when it marks the other as been down. 

Cheers


-----------------
Aaron Morton
Freelance Developer
@aaronmorton

On 1/02/2012, at 11:12 PM, Rene Kochen wrote:

I have a cluster with seven nodes.
 
If I run the node-tool ring command on all nodes, I see the following:
 
Node1 says that node2 is down.
Node 2 says that node1 is down.
All other nodes say that everyone is up.
 
Is this normal behavior?
 
I see no network related problems. Also no problems between node1 and node2.
I use Cassandra 0.7.10
 
Thanks,
 
Rene