7.2 Configuring X.25
7.2.6 Configuring X.25 packet sizes
The x25 ips and x25 ops commands set the default maximum input/output packet size:

To set the incoming packet size, use the x25 ips command:

Router(config-if)#x25 ips bytes

To set the outgoing packet size, use the x25 ops command:

Router(config-if)#x25 ops bytes

The Table describes the x25 ips and x25 ops command.

The input and output values should match unless the network supports asymmetric transmissions. If the stations of an X.25 attachment conflict on the maximum packet size of the VC, the VC is unlikely to work.

Fragmentation is a feature of X.25. The PAD will reassemble the IP packet at the destination.

Before configuring the maximum packet size on your X.25 WAN connection, ask your service provider the maximum packet size it supports.