Chapter 13: AI2524 Frame Relay Configuration Steps
August 1997 Page 13-27
2524UM
Example: Transparent Bridging Using Subinterfaces
In this example, Frame Relay DLCIs 42, 64, and 73 are to be used as
separate point-to-point links with transparent bridging running over
them. The bridging spanning tree algorithm views each PVC as a sep-
arate bridge port, and a frame arri ving on the PVC can be relayed back
out a separate PVC. Be sure that routing is not enabled when config-
uring transparent bridging using subinterfaces.
interface serial 0
encapsulation frame-relay
interface serial 0.1 point-to-point
bridge-group 1
frame-relay interface-dlci 42
interface serial 0.2 point-to-point
bridge-group 1
frame-relay interface-dlci 64
interface serial 0.3 point-to-point
bridge-group 1
frame-relay interface-dlci 73
Configure a Backup Interface for a Subinterface
Both point-to-point and multipoint Frame Relay subinterfaces can be
configured with a backup interface. This approach allows individual
PVCs to be backed up in case of failure rather than d ependin g on th
entire Frame Relay connection to fail before the backup takes over.
You can configure a subinterface for backup on failure only, not for
backup based on loading of the line.
If the serial interface has a backup interface, it will have precedenc
over the subinterface's backup interface in the case of complete loss o
connectivity with the Frame Relay networ k. As a result, a subinterface
backup is activated only if the serial interface is up, or if the serial in-
terface is down and does not have a backup interface defined. If a sub-
interface has failed while its backup is in use, and then the serial
interface goes down, the subinterface backup stays connected.
Beginning in global configuration mode, configure a backup interface
for a Frame Relay subinterface:
1. Specify the interface.
interface serial
number
2. Configure Frame Relay encapsulation.
encapsulation frame-relay