Ethernet switched IP LAN with NW 5.1 SP6 and NW 6.0 SP3 servers
Installed new LAN fiber main switch - Cisco Catalyst 4506

After changing our main fiberswitch from Nortel Accellar 1200 to
Cisco Catalyst 4506, we experience communication problems.

The problems seems unstable and inconsistent, but the following
problems have been observed:
1. NSS volumes sometimes cannot be mapped
2. Server performance sometimes drastically drops (due to
communication problems?)
3. Copying/creating files larger than 1422 byte sometime fails
4. Browsing the internet results only in partially dowloaded pages.
Page load seems to halt, and refreshing the pages reports site not

We suspect this to have something to do with the new switch's handling
of MTU size.
When changing the Novell client MTU size from default 1500 to i.e.
copying files larger than 1422 bytes works OK. We have managed to walk
the server communication problems by physically changing NIC's, or byupdating LAN drivers, but still things occasionally fails. Other problems simply persists.

If we must statically tune the MTU size in the switch in any way, what
should it be,
in a pure IP Ethernet environment?

Or any other ideas?