Usage Guidelines
Many DLCIs can be known by a router or access server and can send
data to many different places, but they are all multiplexed over one physical
link. The Frame Relay map defines the logical connection between a specific
protocol and address pair and the correct DLCI or PVC bundle.
The optional
ietf and
cisco keywords allow flexibility in the
configuration. If no keywords are specified, the map inherits the attributes
set with the
encapsulation frame-relay command. You can also use the
encapsulation options to specify, for example, that all interfaces use IETF
encapsulation except one, which needs the original Cisco encapsulation method
and can be configured through use of the
cisco keyword with the
frame-relay map command.
Data-stream compression is supported on interfaces and virtual
circuits (VCs) using Cisco proprietary encapsulation. When the
data-stream stac keyword is specified, Cisco encapsulation is
automatically enabled. FRF.9 compression is supported on IETF-encapsulated VCs
and interfaces. When the
frf9 stackeyword is specified, IETF encapsulation is automatically
enabled.
Packet-by-packet compression is Cisco-proprietary and will not
interoperate with routers of other manufacturers.
You can disable payload compression by entering the no frame-relay map payload command and then entering the
frame-relay map command again with one of the other
encapsulation keywords (ietf or
cisco).
Use the
frame-relay mapcommand to enable or disable payload compression on multipoint
interfaces. Use the
frame-relay payload-compressioncommand to enable or disable payload compression on
point-to-point interfaces.
We recommend that you shut down the interface before changing
encapsulation types. Although shutting down the interface is not required, it
ensures that the interface is reset for the new encapsulation.
The
broadcast keyword provides two functions: it
forwards broadcasts when multicasting is not enabled, and it simplifies the
configuration of OSPF for nonbroadcast networks that will use Frame Relay.
The
broadcast keyword may also be required for
some routing protocols--for example, AppleTalk--that depend on regular routing
table updates, especially when the router at the remote end is waiting for a
routing update packet to arrive before adding the route.
By requiring selection of a designated router, OSPF treats a
nonbroadcast, multiaccess network such as Frame Relay in much the same way as
it treats a broadcast network. When the
frame-relay map command (with the
broadcast keyword) and the
ip ospf networkcommand (with the
broadcast keyword) are configured, there is
no need to configure any neighbors manually. OSPF will run automatically over
the Frame Relay network as a broadcast network. (See the
ip ospf network interface command for more detail.)
Note |
The OSPF broadcast mechanism assumes that IP class D addresses are
never used for regular traffic over Frame Relay.
|
Examples
The following example maps the destination IP address 172.16.123.1 to
DLCI 100:
interface serial 0
frame-relay map ip 172.16.123.1 100 broadcast
OSPF will use DLCI 100 to broadcast updates.
The following example maps the destination IP address 172.16.123.1 to
the Frame Relay PVC bundle named “MAIN-1”:
interface serial 0
frame-relay map ip 172.16.123.1 vc-bundle MAIN-1 broadcast
The following example shows FRF.9 compression configuration using
the frame-relay mapcommand:
interface serial2/0/1
ip address 172.16.1.4 255.255.255.0
no ip route-cache
encapsulation frame-relay ietf
no keepalive
shutdown
frame-relay map ip 172.16.1.1 105 ietf payload-compression frf9 stac
The following example shows data-stream compression configuration
using the
frame-relay map command:
interface serial0/0
frame-relay map ip 10.0.0.1 100 payload-compression data-stream stac