User Manual

Physical and Layer 2 Interfaces 71
Software Release 2.5.2
C613-02034-00 REV A
3. Add logical interfaces if required
Frame Relay logical interfaces (FRLI) provide a mechanism for organising
DLCs into groups. Each FRLI, or group of DLCs, are assigned its own IP
address to split the Frame Relay network into subnets. A default FRLI 0 is
always created when a Frame Relay interface is created. To create
additional FRLI’s, enter the command:
ADD FRAMERELAY=fr-interface LI=logical-interface
By default, all DLCs are associated with the default FRLI 0. To associate
DLCs with other FRLIs, enter the command:
SET FRAMERELAY=fr-interface DLC=dlci LI=logical-interface
4. Enable routing modules to use the interface
Once a Frame Relay interface is defined and configured, configure routing
modules to use the interface. The procedures for achieving this are
described in the chapter for the particular routing module.
In general, commands that contain the parameter INTERFACE= can refer
to a Frame Relay interface by name. The form of the name is “frn”, where n
is the instance for the Frame Relay module. Examples of commands that
can refer to a Frame Relay interface include:
ADD IP INTERFACE=FRn...
ADD IPX CIRCUIT=circuit INTERFACE=FRn...
SET DNT ADD=INTERFACE INTERFACE=FRn...
One important point concerning the use of Frame Relay interfaces by the IP
routing module is the way that the IP routing module maps IP addresses to
a Frame Relay DLCI and vice versa. This mapping is an example of
Address Resolution Protocol or ARP. Two methods of ARP are supported
for Frame Relay interfaces on the router, Inverse ARP and static ARP.
The router supports the Inverse ARP, a protocol specially developed for
Frame Relay that involves the exchange of packets between routers
connected by a DLC in order to map an IP address to a Data Link
Connection Identifier (DLCI). Inverse ARP is described in RFC 1293.
To enable the router to communicate with DTEs that do not support
Inverse ARP, static ARP entries are added, by entering the command:
ADD IP ARP=ipadd INTERFACE=FRn DLCI=dlci
The use of static DLCs and static ARP information is not normally required for
interoperation of the router with other vendors’ equipment. These facilities are provided
for interoperation with equipment that does not fully support the Frame Relay
standards. Networks that consist purely of routers that support Inverse ARP will not
need static ARPs.