Whenever you use encryption services or any encapsulation technique, packet size and fragmentation become an issue. The SteelHead is aware of which paths are using an encapsulation technique, such as firewall traversal or secure transport, and lowers the TCP maximum segment size (MSS) as part of the initial setup of the connection. This behavior occurs for pass-through and accelerated traffic and minimizes the possibility for fragmentation.

The secure transport feature uses more overhead than the 24 bytes for the generic routing encapsulation (GRE) header used in the firewall traversal feature but operates in the same manner. For information about maximum transmission unit (MTU) considerations for the firewall traversal feature, see the SteelHead Deployment Guide.