How to Configure Frame-relay interfaces
Frame relay interfaces can be configured as Physical, Multipoint and point-to-point interfaces. Frame relay routing protocols and mostly all network configuration is heavily affected by interface type selected.
In the following digram R1 is connected to R2 using frame-relay and we are going to explore different configuration options.
Task1: Configure frame-relay PVC between R1 and R2 using physical
Physical interfaces are considered to be multipoint interfaces by default, which means that address resolution is essential in order for both ends to communicate.
Address resolution can be accomplished manually using the frame-relay map command or dynamically using inverse ARP.
Dynamic address resolution using InArp:
R1 configuration:
| R1(config)#int s1/0 R1(config-if)#encapsulation frame-relay R1(config-if)#frame-relay inverse-arp R1(config-if)#ip address 10.10.12.1 255.255.255.0 R1(config-if)#no shut |
R2 configuration:
| R2(config)#int s1/0 R2(config-if)#encapsulation frame-relay R2(config-if)#frame-relay inverse-arp R2(config-if)#ip address 10.10.12.2 255.255.255.0 R2(config-if)#no shut |
Configuration Notes:
DLCI is automatically received from the frame-relay switch and assigned to the physical interface by default. we don't need to make any special configuration for DLCIs when using physical interfaces. Frame relay address resolution is accomplished dynamically using inverse ARP as shown in the following commands output.
Verification and troubleshooting:
| R1#ping 10.10.12.2
Type escape sequence to abort. R1#sh frame-relay map R2#ping 10.10.12.1 Type escape sequence to abort. R2#sh frame-relay map |
Manual address resolution:
If Inverse ARP requests are disabled, address resolution must be configured manually using the frame-relay map command.
| R1(config)#int s1/0 R1(config-if)#no frame-relay inverse-arp R1(config-if)#frame-relay map ip 10.10.12.2 102 broadcast R2(config)#int s1/0 |
The broadcast keyword is optional but recommended as it allows broadcast and multicast traffic to traverse the PVC.
Verification and troubleshooting:
| R1#ping 10.10.12.2
Type escape sequence to abort. R1#sh frame-relay map R2#ping 10.10.12.1 Type escape sequence to abort. R2#sh frame-relay map |
Task2: configure the frame-relay connection between R1 and R2 using multipoint sub interfaces:
Dynamic address resolution:
| R1(config-subif)#int s1/0 R1(config-if)#encapsulation frame-relay R1(config-if)#int s1/0.21 multipoint R1(config-subif)#ip address 10.10.12.1 255.255.255.0 R1(config-subif)#frame-relay interface-dlci 102 R2(config)#int s1/0 |
Verification and Troubleshooting:
| R1#sh frame-relay map Serial1/0.21 (up): ip 10.10.12.2 dlci 102(0x66,0x1860), dynamic, broadcast,, status defined, active R2#sh frame-relay map |
Manual address resolution:
| R1(config-subif)#int s1/0.21 R1(config-subif)#frame-relay map ip 10.10.12.2 102 broadcast R2(config-subif)#int s1/0.21 R1#show frame-relay map R2#sh frame-relay map |
Task3: Configure frame-relay connection between R1 & R2 using point-to-point subinterfaces.
Point-to-Point interfaces do not need any kind of address resolution, only the DLCI must be assigned to the subinterface using the frame-relay interface-dlci command.
| R1(config)#int s1/0 R1(config-if)#encapsulation frame-relay R1(config-if)#int s1/0.12 point-to-point R1(config-subif)#ip address 10.10.12.1 255.255.255.0 R1(config-subif)#frame-relay interface-dlci 102 R2(config)#int s1/0 |
Verification and Troubleshooting:
| R1#sh frame-relay map Serial1/0.12 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast status defined, active R2#sh frame-relay map |
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