We have 2 locations (using 6500's in hybrid mode) in our WAN that are connected our main bulding (using a 3550-12G) via fiber from Comcast. Both connections run over seperate VLANS on Comcast's network to their switches on sites. Our interfaces on their switches are access ports, so their vlans are transparent to us. They have set their MTU to 1504 to allow for 802.1Q tagging on their network. WE can pass 1500 byte packets with no difficulty.
Currently, I have seperate vlans at each site with a VLAN (499) connectinng all 3 sites. I am statically routing between all 3 sites using vlan 499. I have added another VLAN (808) to span all 3 sites for virtual server redundancy for all 3 sites.
The problem I am having is that I cannot send packets any larger than 1496 bytes across the new vlan(808). The vlan 499 does not have any problems with 1500 byte packets.
Anyone have any ideas why this is?