I'm handling a case where changing the mtu size of the packet is needed to have traffic passing through a GRE tunnel. The only thing that solves the issue is either reducing the ip tcp adjust-mss on the interface or the mss on the device.
Unfortunatelly customer doesn't have routers where to set the tcp adjust-mss command, only layer 3 switches where the command is not supported.
More specifically 6500 are not supporting tcp adjust command.
I tried workarounds like setting a PBR to set the DF bit to 0 for the traffic that will go over the tunnel, changing the mtu size on the tunnel to 1400 and 1600 but neither work, it seems that the remote server doesn't accept fragmented packets.
Lowering the MTU on the pc solves the problem but customer didn't like the workaround.
I wanted to know if you have any other workaround I could try to fix this kind of issues for this platform.