Odd network issue - VM's in certain IP range can't be accessed when on specific host

[maytrix0]

This is an odd one that I haven't seen before. It started without any changes being made.  We just had an issue one day with users being unable to connect and I narrowed it down to it having something to do with the hosts.  We initially thought it may have had to do with a switch, but it seems that isn't the case.

Here's what I've found now.  In testing out one of the hosts, I moved a number of VM's back to it.  I discovered that some of the VM's weren't reachable.

Our LAN is 192.168.0.1 with a subnet of 255.255.254.0.

Systems that are in the 192.168.1.X range could be accessed on this host.  Systems that were in the 192.168.0.X range cannot be accessed on this host.  I don't see anything anywhere in the network that would impede this and the ports on the switch are fine as well.

Any thoughts on what might cause this or where to look?

Thanks

[vcallaway]

Is the issue happening across hosts or isolated to inter-host communication?

[sjesse]

Do you also use vlans? If that range is in a certain vlan, you will want to check the vswitchs on that host. There are portgroups probably, one for each network range, see if you can find that one and if you try and edit it there should be vlan tagging option.

[maytrix0]

It is across hosts.

Interestingly enough I moved 2 VM's to the host having issues.  One was 192.168.0.5 and the other 192.168.0.55.  The .55 server could communicate with everything.  The .5 server could only communicate with the .55 server and nothing else.

We use VLANS, but untagged.  So the nics on all the hosts for the LAN are in the default VLAN.  iSCSI and VMotion traffic are in different VLANS.

[maytrix0]

So..  I think the problem is resolved.

The one host having issues was running 5.5.  Our other hosts 6.0.  We simply had it on 5.5 since we had issues updating it previously and didn't have an urgent need to upgrade it.  I decided to try it again and it worked and the problem is resolved.  I'm not sure why, since this has been running like this for over a year and we haven't done any updates prior to the issue occurring.  Regardless, I'm glad it is resolved.  We'll be replacing the hosts soon and upgrading but wanted this resolved in the meantime.

Thanks for the input!