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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.
Sending 5, 100-byte ICMP Echos to 10.10.12.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 40/112/232 ms

R1#sh frame-relay map
Serial1/0 (up): ip 10.10.12.2 dlci 102(0x66,0x1860), dynamic,
broadcast,
CISCO, status defined, active

R2#ping 10.10.12.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.12.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 28/114/288 ms

R2#sh frame-relay map
Serial1/0 (up): ip 10.10.12.1 dlci 201(0xC9,0x3090), dynamic,
broadcast,
CISCO, status defined, active

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
R2(config-if)#no frame-relay inverse-arp
R2(config-if)#frame-relay map ip 10.10.12.1 201 broadcast

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.
Sending 5, 100-byte ICMP Echos to 10.10.12.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 36/155/376 ms

R1#sh frame-relay map
Serial1/0 (up): ip 10.10.12.2 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active

R2#ping 10.10.12.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.10.12.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/101/248 ms

R2#sh frame-relay map
Serial1/0 (up): ip 10.10.12.1 dlci 201(0xC9,0x3090), static,
broadcast,
CISCO, status defined, active

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
R2(config-if)#encapsulation frame-relay
R2(config-if)#int s1/0.21 multipoint
R2(config-subif)#ip address 10.10.12.2 255.255.255.0
R2(config-subif)#frame-relay interface-dlci 201

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
Serial1/0.21 (up): ip 10.10.12.1 dlci 201(0xC9,0x3090), dynamic,
broadcast,, status defined, active

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
R2(config-subif)#frame-relay map ip 10.10.12.1 201 broadcast

R1#show frame-relay map
Serial1/0.21 (up): ip 10.10.12.2 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active

R2#sh frame-relay map
Serial1/0.21 (up): ip 10.10.12.1 dlci 201(0xC9,0x3090), static,
broadcast,
CISCO, status defined, active

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
R2(config-if)#encapsulation frame-relay
R2(config-if)#int s1/0.12 point-to-point
R2(config-subif)#ip address 10.10.12.2
R2(config-subif)#frame-relay interface-dlci 201

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
Serial1/0.12 (up): point-to-point dlci, dlci 201(0xC9,0x3090), broadcast
status defined, active

3 comments

  1. Dear Wael,

    Thanks for the post :) but I have a question to sort this topic out.

    1- Why do we need to assign interface DLCI when using sub interfaces? Is it because:

    – ILMI doesn’t work, somehow, correctly with sub interfaces affecting automatic assignment of DLCIs from the local FR switch?

    – Sub interface is by default a point to point network type, but if configured as a multipoint type, it should work fine?

    What I want to know here is that: Is the physical “mutlipoint” or sub interface “multipoint” working as one BIG exiting interface which has some logical ones, and to send data using this “one big interface”, weather it’s a physical or multipoint subinterface, it should be assigned to a “small logical one” which is DLCI?

    2- What is the difference between using Multipoing and NMBA in OSPF design? If the full mesh is not an issue?

    Thanks for your time.

  2. Hi Kamal,

    The “frame-relay interface-dlci” command is used when we make point-to-point sub-interfaces. For point-to-point sub-interfaces, we must use this “frame-relay interface-dlci” statement. We cannot use the “frame-relay map” command. The “frame-relay map” command can be used for physical interfaces (e.g. serial 0/0) or multipoint sub-interfaces (e.g. serial 0/0.1 multipoint). We usually make use of sub-interfaces to get around the split-horizon non-advertisement problem.

    NBMA is used to denote technologies like frame-relay. As an example, if we typed, “no frame-relay inverse-arp” (see Task 1 above), and then followed with a frame map statement, e.g. “frame-relay map ip 10.10.12.2 102” without the broadcast parameter, this is an acceptable statement, i.e. . We can sent pings around, but note that ping is unicast. When we try to run our dynamic routing protocol over this NBMA (say frame-relay) network, we are not able to do so. Why? Remember that we left out the broadcast parameter of the “frame-relay map” statement. Taking RIP as an example, RIP V1 is broadcast and RIP V2 is multicast (224.0.0.9). As the names NBMA (non-broadcast multiple access) denotes, it does not work. Try comparing this with a broadcast medium e.g. Ethernet.

    I hope this helps.

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