AnyConnect MTU Size

ben.wiechman · ‎04-16-2009

Going through the release notes for AnyConnect 2.3 it gives the example that the MTU size is set to 1406 bytes just after Figure 11, but includes no explanation. Is this just an example of how to change the MTU size or is this a recommendation for optimal performance?

Does anyone know?

smalkeric · ‎04-22-2009

You can adjust the Maximum Transmission Unit size (from 256 to 1406 bytes) for SSL VPN connections established by the AnyConnect Client by using the svc mtu command from group policy webvpn or username webvpn configuration mode:

[no] svc mtu size

This command affects only the AnyConnect Client. The Cisco SSL VPN Client (SVC) is not capable of adjusting to different MTU sizes.

The default size for this command in the default group policy is 1406. The MTU size is adjusted automatically based on the MTU of the interface that the connection uses, minus the IP/UDP/DTLS overhead.

This command affects AnyConnect Client connections established in SSL and those established in SSL with DTLS.

The following example configures the MTU size to 1200 bytes for the group policy telecommuters:

hostname(config)# group-policy telecommuters attributes

hostname(config-group-policy)# webvpn

hostname(config-group-webvpn)# svc mtu 1200

ben.wiechman · ‎04-22-2009

So the example of 1406 bytes was completely arbitrary?