This document does a good job of showing how the Interconnections work.  www.dell.com/.../ps3q05-20050163-Brundridge-OE.pdf I/O module 1 will go to port 1 and I/O module 2 will go to port 2 of the LOM. So it may be worth checking which ports are being used by the server. If 3 are on port 1 and then the other 2 are on port 2, try and get all the 172.50.1.x addresses assigned to port 2 for example.
Hi, I have recently put one of our old clusters back online, its a poweredge 1855. I'm working on 5 nodes, and it has a PowerConnect 5316M on the back. The 5316M has only 1 cable connecting it to the uplink switch. Each blade has 2 NIC's. One of them is a normal production NIC, with a normal IP on our range. All blades can ping each other on this address, and they all have internet. The other NIC is what I'm going to use for live migration, or cluster heartbeat or something ..either way, it has a different range with no gateway (172.50.1.x) Now, 3 of the blades can all ping eachother, but not the other 2. And the 2 that cant ping, can ping eachother. So it looks like 2 are on the same VLAN, and the other 3 are on the same VLAN. The problem i have, is the switch shows them all on the default VLAN ..and one thing i cant work out ..is if the servers all have 2 NICs, but there are only 10 internal switch ports? ..so how can i set either NIC on a different VLAN? The switch config is here: 
Cluster nodes cant ping each other