Packet reassembly

Packet size and fragmentation#

Packets received that are larger than the MTU (Maximum Transmissible Unit) of the connection will be fragmented automatically at the kernel level in linux.

Packet reassembly is handled in a similar way.

MTU tuning#

Connections are tuned for MTU on calibration and commissioning. MSS (Maximum Segment Size) is set so that TCP based traffic flows are informed of the MTU accordingly to avoid fragmentation wherever possible.

Set MTU on router/firewall#

Whatever the device used to connect to an EVX at an edge site, it should be set with the MTU of the overall aggregated connection to avoid fragmentation

The MTU can be determined by running a series of pings with different MTUs.

It is especially important to set the MTU when running certain VPNs over a connection. The encapsulated packets of the VPN will need a smaller MTU to cope with the extra overhead of the VPN.