Configure Frame Relay in Point-to-Point

Configuring Frame Relay in Point-to-Point topology on Cisco IOS.

Configuring Frame Relay on Cisco Systems router is not so difficult and takes several minutes. My virtual lab consists of Dynamips network simulator running on Ubuntu. Here is the topology we will use:

In Frame Relay Point-to-Point topology every pair of routers have their own subnet (usually /30). It is not a good solution if you are running out of IP addresses in your network – in every subnet used for connecting routers, 2 of 4 available addresses are wasted for network address and broadcast address.

However configuring Frame Relay with point-to-point sub-interfaces avoids problem of split horizon rule that can appear when using distance vector routing protocols such as RIP orEIGRP.

Synopsis:

What we are going to do is configure routers R1, R2 and R3 with point-to-point sub-interfaces. We will use inverse ARP for IP to DLCI mapping. We will also configure Frame Relay switch (FRSWITCH). So, let’s get this network started!

First, we will configure Frame Relay switch. After enabling switching on router we will make some routes and specify interface type to be a DCE (by default a router is considered to be a DTE device).

FR-SWITCH(config)#frame-relay switching

FR-SWITCH(config)#int s 1/0

FR-SWITCH(config-if)#encapsulation frame-relay

FR-SWITCH(config-if)#frame-relay intf-type dce

FR-SWITCH(config-if)#frame-relay route 102 interface serial 1/1 201

FR-SWITCH(config-if)#frame-relay route 103 interface serial 1/2 301

FR-SWITCH(config-if)#no shutdown

FR-SWITCH(config-if)#int serial 1/1

FR-SWITCH(config-if)#encapsulation frame-relay

FR-SWITCH(config-if)#frame-relay intf-type dce

FR-SWITCH(config-if)#frame-relay route 201 interface s1/0 102

FR-SWITCH(config-if)#frame-relay route 203 interface s1/2 302

FR-SWITCH(config-if)#no sh

FR-SWITCH(config-if)#int s 1/2

FR-SWITCH(config-if)#encapsulation frame-relay

FR-SWITCH(config-if)#frame-relay intf-type dce

FR-SWITCH(config-if)#frame-relay route 301 interface s1/0 103

FR-SWITCH(config-if)#frame-relay route 303 interface s1/1 203

FR-SWITCH(config-if)#no sh

To examine and verify route statements type show frame-relay route

FR-SWITCH#show frame-relay route

 Input Intf     Input Dlci     Output Intf     Output Dlci     Status

 Serial1/0       102         Serial1/1       201         active

 Serial1/0       103         Serial1/2       301         active

 Serial1/1       201         Serial1/0       102         active

 Serial1/1       203         Serial1/2       302         active

 Serial1/2       301         Serial1/0       103         active

 Serial1/2       302         Serial1/1       203         active

Now we have to configure3 remaining routers. Configuration on each router will be very similar – after enabling FR encapsulation we will specify interface DLCI and IP address.

R2(config)#int s 1/0

R2(config-if)#encapsulation frame-relay

R2(config-if)#no ip add

R2(config-if)#clock rate 128000

R2(config-if)#no sh

R2(config)#int s 1/0.201 point-to-point

R2(config-subif)#ip add 10.1.1.2 255.255.255.252

R2(config-subif)#frame-relay interface-dlci 201

R2(config)#int s1/0.203 point-to-point

R2(config-subif)#ip add 10.1.1.9 255.255.255.252

R2(config-subif)#frame-relay interface-dlci 203

On router R1:

R1(config)#int s 1/0

R1(config-if)#encap frame

R1(config-if)#clock rate 128000

R1(config-if)#no sh

R1(config)#int s 1/0.102 point-to-point

R1(config-subif)#ip add 10.1.1.1 255.255.255.252

R1(config-subif)#frame-relay interface-dlci 102

R1(config)#int s1/0.103 point-to-point

R1(config-subif)#ip add 10.1.1.5 255.255.255.252

R1(config-subif)#frame-relay interface-dlci 103

And on R3:

R3(config)#int s 1/0

R3(config-if)#enc frame

R3(config-if)#enc frame-relay

R3(config-if)#clock rate 128000

R3(config-if)#no sh

R3(config)#int s 1/0.301 point-to-point

R3(config-subif)#ip add 10.1.1.6 255.255.255.252

R3(config-subif)#frame-relay interface-dlci 301

R3(config)#int s 1/0.302 point-to-point

R3(config-subif)#ip add 10.1.1.10 255.255.255.252

R3(config-subif)#frame-relay interface-dlci 302

Now, we can examine FR map f.e on R1:

R1#sh frame-relay map

Serial1/0 (up): ip 0.0.0.0 dlci 103(0x67,0x1870)

 broadcast,

 CISCO, status defined, active

Serial1/0 (up): ip 0.0.0.0 dlci 102(0x66,0x1860)

 broadcast,

 CISCO, status defined, active

Serial1/0.102 (up): point-to-point dlci, dlci 102(0x66,0x1860), broadcast

 status defined, active

Serial1/0.103 (up): point-to-point dlci, dlci 103(0x67,0x1870), broadcast

 status defined, active

Everything seems valid all circuits are in active state. Let’s perform a ping.

R1#ping 10.1.1.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.1.1.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 48/80/108 ms

Our network works. That’s all about Frame Relay in Point-to-Point topology.