We have a strange issue where every time we try to enable a trunk on our VSS switches, we lose our EIGRP adjacencies. We have an 8-port 10GE blade in slot 9, and we are using ports 1/5/4, 2/5/4, 1/9/8 and 2/9/8 for our links between the 2 chassis. We deployed 2 new 6120 fabric interconnects for our UCS project. When I try to enable port 1/9/1, I lose my EIGRP adjacencies to my 2 core switches. On 1/5/5, I have a link through a 4270 IPS going to core1, using a /30 on vlan X. On 2/5/5, I have a similar setup going to core2. Obviously losing all connectivity to my server farm is bad, so I can't leave the link on to troubleshoot. Any ideas as to what might be causing this? I have tried it in the past, and that's how we ended up with the routed server farm block. I wanted to trunk the vlans to the server VSS switch, but it kept dropping EIGRP adjacencies. Ports on blades 1 or 2 in the VSS work fine as trunks, and ports in blade 9 work as access. I attached a crappy network diagram. Thanks.