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ImageStream - Frame Relay Configuration

Frame Relay Configuration

A Frame Relay network represents two or more routers interconnected by a Frame Relay cloud. Each router on the Frame Relay cloud is connected to the Frame Relay network that has a Permanent Virtual Circuit (PVC). The Frame Relay network is connected to a Frame Relay switch that in turn connects to the Frame Relay cloud.

The interface or port used to connect the router to the Frame Relay network is called a Frame Relay interface and each Frame Relay interface must have an IP address.

  • Each router is a node on the Frame Relay network.
  • The Frame Relay network has its own IP network number that is normally a class C or a subnet of a class C that is unique from other subnets on the system.
  • Each router Frame Relay interface (port) is assigned an IP address from the Frame Relay network's subnet, thus the netmask for each Frame interface on each router of the Frame Relay network is the same.
  • Data Link Connector Identifier (DLCI) numbers are used to point from the Frame Relay switch located at the telephone company central office, to the PVC of a router(s) on the other side of the Frame cloud.
  • The router communicates with the switch by polling the switch at a manually configured polling interval. The default value is 10 seconds.
  • The router can communicate with the switch using Local Management Interface (LMI) or Annex-d  signaling. If the router receives 3 LMI packets back from the switch the connection is established, and the interface statistics (stats) will show the protocol status as "up". If LMI packets are not present  the connection (protocol in the stats interface) will go down.
  • When using LMI the switch will respond with a full DLCI list after a few exchanges of LMI packets. The router can use this information to build a dynamic DLCI list or the DLCI list can be set up statically.
====ETHERNET===================== ===
        | LAN IP:
|                |
|  Router A      |
|   Serial0      |
        | WAN IP:
       [-] CSU/DSU
        |Frame Relay Cloud WAN
        |                            |
       [-] CSU/DSU                   | WAN IP:
        |                    +-------+-------+
        | WAN IP:|   Serial0     |
+-------+--------+           |  Router C     |
|   Serial0      |           |               |
|  Router B      |           +-------+-------+
|                |                   | LAN IP: 192.168.300.300
+-------+--------+  ===ETHERNET=======
        | LAN IP:
====ETHERNET===================== ===

Configuring IP Over Frame Relay

The following is a sample of a port configuration: 

  • For this example: The Frame Relay interface on the router is Serial0
  • For this example: The IP address of the Frame Relay connection on the router is
# Comments (denoted by a hash mark at the beginning of the line)
# are permitted anywhere in the file
# See the Command Reference for more information on the
# commands below
version 2.00
interface Serial0
 description Port 0
 encapsulation frame-relay ietf
 frame-relay lmi-type ansi
# frame-relay lmi-type ccitt
# frame-relay lmi-type cisco
interface Serial0.1
 description UUNet T1
 encapsulation frame-relay ietf
 frame-relay interface-dlci 500
 ip address
ip route Serial0.1

At this point, LMI packets should be being transmitted and received. The status of the WAN port should change to up. It should now be possible to ping the other side. The interface statistics (Option 2 from the Main menu) should show:

19:03:17              Interface Summary                              Router A
#  Port      Description        Encaps       Bandwidth    HW  Proto  In   Out
 0 Ethernet0 100Mb Ethernet     Ethernet     100.00 Mbit  up   up     0%   0%
 1 Serial0   Port 0             Frame Relay    1.54 Mbit  up   up     0%   0%
 2   Serial0.1   UUNet  T1                     1.54 Mbit  up   up     0%   0%
d - Detail  s - Sleep interval  q - Quit