AIS Router AI2524 - Manual (Page 274)

AI2524 Router Card User’s Manual
Page 12-16 August 1997
2524UM
Note: When configuring IP routing over X.25, you might need
to make adjustments to accommodate split horizon effects.
Refer to the Configuring IP Routing Protocols chapter in
the Network Protocols Configuration Guide, Part 1 for
details about how the Cisco IOS software handles possible
split horizon conflicts. By default, split horizon is enabled
for X.25 networks.
Example: Point-to-Point Subinterface Configuration
This example creates a point-to-point subinterface and maps IP to a re-
mote host:
interface Serial0.1 point-to-point
x25 map ip 172.20.170.90 170090 broadcast
Map Protocol Addresses to X.121 Addresses
This section describes the X.25 single-protocol and multiprotocol en-
capsulation options that are available and describes how to map proto-
col addresses to an X.121 address for a remote host. This section also
includes reference information about how protocols are identified.
Understand Protocol Encapsulation for Single-Protocol and
Multiprotocol Virtual Circuits
The AI2524 supports encapsulation of a number of datagram protocols
across X.25, using a standard method when available, or a proprietary
method when necessary. These traditional methods assign a protocol
to each virtual circuit. If more than one protocol is carried between th
router and a given host, each active protocol will have at least one vir-
tual circuit dedicated to carrying its datagrams.
The AI2524 also supports RFC 1356, a standardized method for en
capsulating most datagram protocols over X.25. It also specifies ho
one virtual circuit can carry datagrams from more than one protocol.
The Cisco IOS software can be configured to use any of the available
encapsulation methods with a particular host.
After you establish an encapsulation virtual circuit, the Cisco IOS soft-
ware sends and receives a datagram by simply fragmenting it from and
reassembling it into an X.25 complete packet sequence. An X.25 com-
plete packet sequence is one or more X.25 data packets that have the
M-bit set in all but the last packet. A virtual circuit that can carry mul-
tiple protocols includes protocol identification data as well as the pro-
tocol data at the start of each complete packet sequence.