DB2 is installed on a single node. Last night out network guys failed over to a different server, which did not match the server entry in the db2nodes.cfg file and db2 crashed. Is db2nodes.cfg required if you only have one node? Any ideas how to avoid this issue?

DB21085I Instance "db2inst1" uses "32" bits and DB2 code release "SQL08022"
with level identifier "03030106".
Informational tokens are "DB2 v8.1.0.89", "special_15295", "U800790_15295", and
FixPak "9".
Product is installed at "/opt/IBM/db2/V8.1".

yes it is. One way to avoid this may be is to create another nodes.cfg file and rename current nodes.cfg to something else and this file to db2nodes.cfg before the database comes up on the alternate server. However, this may only serve the database coming up - it does not address the accessiblity issue. For that you would need virtual hostname with failover capabilities at the host level.

Hope this helps.