AIS AI2524 user manual Example Typical X.25 Configuration

Chapter 12: AI2524 X.25 Configuration Steps

maximum packet sizes. PVCs also use these default values unless dif- ferent values are configured.

In interface configuration mode, set the default input and output max- imum packet sizes:

1.Set the default input maximum packet size. x25 ips bytes

2.Set the default output maximum packet size. x25 ops bytes

To send a packet larger than the agreed on X.25 packet size over an X.25 virtual circuit, the Cisco IOS software must break the packet into two or more X.25 packets with the M-bit (More data bit) set. The re- ceiving device collects all packets in the M-bit sequence and reassem- bles them into the original packet.

It is possible to define default packet sizes that cannot be supported by the lower layer (see the LAPB N1 parameter). However, the router will negotiate lower maximum packet sizes for all SVCs so the agreed on sizes can be carried. The Cisco IOS software will also refuse a PVC configuration if the resulting maximum packet sizes cannot be sup- ported by the lower layer.

Example: Typical X.25 Configuration

This example shows the complete configuration for a serial interface connected to a commercial X.25 PDN for routing the IP protocol. The IP subnetwork address 172.25.9.0 has been assigned for the X.25 net- work.

Note:	When you are routing IP over X.25, you must treat the
	X.25 network as a single IP network or subnetwork. Map
	entries for routers with addresses on subnetworks other
	than the one on which the interface's IP address is stored
	are ignored by the routing software. All routers using the
	subnet number must have map entries for all others
	routers. Using the broadcast option with dynamic routing
	can result in larger traffic loads, requiring a larger hold
	queue, larger window sizes, or multiple virtual circuits.

August 1997	Page 12-7
2524UM