FIGURE-1: Pseudo Broadcast and Routing Protocols


In figure-1, the routing protocol is RIP version 1. R4 is advertising to R3. Since updates are sent as broadcast, R3 will replicate the update as pseudo broadcast (or replicated unicast) to R1 and R2. The “frame relay map” statement requires the “broadcast” keyword for this functionality to be enabled. Otherwise, routing protocols like RIP, OSPF and EIGRP and other networking technologies relying either on broadcast or multicast will not work on Frame Relay networks.


Cisco IOS allows the emulating of broadcast (the pseudo broadcast) using the “broadcast” keyword at the end of frame relay DLCI mapping statement.

Step-1: configure terminal

Step-2: interface serial

Step-3: encapsulation frame-relay

Step-4: frame-relay map ip broadcast ß Note the broadcast keyword

Step-5: end


The IP address is the address of far-end device. For example, router-A is being configured to connect to router-B, the IP address of router-B is used. DLCI is local DLCI assigned by the service provider.

Pseudo broadcast is enabled (by-default) when Dynamic Inverse-ARP is used or frame relay is configured in point-to-point configuration. No explicit configuration is required for Inverse-ARP.

Let us consider an example. R3 (from figure-1) is being configured to communicate with R2 and R1. The ISP provided the following details:

  •  No Inverse-ARP
  •  DLCI for R1 circuit is 301
  •  DLCI for R2 circuit is 302
  •  Logical multipoint interface should be used.

The following will be the configuration script:


R3(config)#interface serial0/0

R3(config-if)#encapsulation frame-relay

R3(config-if)#interface serial0/0.123 multipoint

R3(config-subif)#ip add

R3(config-subif)#no frame-relay inverse-arp

R3(config-subif)#frame-relay map ip 301 broadcast

R3(config-subif)#frame-relay map ip 302 broadcast


R3(config)# interface serial0/0

R3(config-if)# no shutdown

R3(config-if)# end


R3#show frame-relay map

Serial0/0.123 (up): ip dlci 301(0x12D,0x48D0), static,


 CISCO, status defined, active

Serial0/0.123 (up): ip dlci 302(0x12E,0x48E0), static,


CISCO, status defined, active

R3#show frame-relay pvc 302

PVC Statistics for interface Serial0/0 (Frame Relay DTE)




input pkts 8 output pkts 8 in bytes 832

out bytes 832 dropped pkts 0 in pkts dropped 0

out pkts dropped 0 out bytes dropped 0

in FECN pkts 0 in BECN pkts 0 out FECN pkts 0

out BECN pkts 0 in DE pkts 0 out DE pkts 0

out bcast pkts 0 out bcast bytes 0

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

pvc create time 00:06:14, last time pvc status changed 00:02:56


Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 96/145/272 ms

R3# R3#ping

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to, timeout is 2 seconds:


Success rate is 100 percent (5/5), round-trip min/avg/max = 99/150/280 ms

This brings us to the end of our discussion of Non-Broadcast Multi-Access networks.