Starting with ExtremeXOS and Switch Engine 31.6, GRE tunnel supports IP Maximum Transmission Unit (MTU) configuration.
When the IP packet size exceeds the configured IP MTU value on a tunnel, the Path MTU (PMTU) mechanism can be used to notify the sender of the traffic that the packet size needs to be reduced.
ExtremeSwitching X590, X690, X695, and X465 series switches.
configure tunnel tunnel_name ip mtu mtu