Hi Steve, Thanks for offering to look. Here's the setup: VLAN ID 99 has 172.31.99.0/24 routed into it VLAN ID 100 has 172.31.100.0/24 routed into it I've got two physical nodes: aphost0 (172.31.99.50 on its eth0 in VLAN ID 99) aphost1 (172.31.100.50 on its eth0 in VLAN ID 100) Each of these servers are dom0 hosts for Xen domU guests using the dom0's bridged eth1. The domU cluster is having the same problem as the dom0 cluster, but let's just ignore that for the time being. Here's what I'm certain about as the network equipment. Both hosts are patched into the same catalyst 2960 G switch. aphost0 into a port assigned to VLAN ID 99 only and aphost1 into a port assigned to VLAN ID 100 only. >From here, I'm less certain, but I think the following is true: The cat 2960 is linked using Rapid Spanning Tree Protocol to two layer 3 switches - a Catalyst 6506 and a Catalyst 3750G-12S. I'm also quite certain that access control lists are applied on these switches, however I had one of the network admins do a quick check on the routers and he said IGMP should be working and the multicast IP range that I've been assigned internally (239.224.72.0/24) has not been used within the university for a long time. Indeed there are some video streams running around the campus using neighbouring ranges of multicast IPs and they seem to work well enough on the same network infrastructure. I've tried disabling iptables on the hosts and still see the same results, so it's not firewalls. Rebooting the nodes is very slow, because they sit for four or five minutes waiting at "Starting fencing ..." I'm going to send you the messages file off-list, it's just a bit too big, especially with all the spurious fencing and multipath errors that are going into it. Regards, Nik Lam -- Linux-cluster mailing list Linux-cluster@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/linux-cluster
