Configure Frame Relay in Multipoint

Configuring Frame Relay in Multipoint topology on Cisco IOS.

Configuration of Frame Relay on Cisco Systems router in multipoint topology is easy as pie and takes several minutes. My virtual lab consists of Dynamips network simulator running onUbuntu. Here is the topology we will use:

In Frame Relay Multipoint topology routers share one subnet. In such a solution IP addresses are saved and are not wasted like in Point-to-point topology. However there is  one drawback – distance vector routing protocols such as RIP or EIGRP may not work correctly because of split horizon rule.

Split horizon blocks sending routing updates from the interface they originated. The fastest solution is to disable split horizon on router’s interfaces – however there is a better one, you can use point-to-point sub-interfaces (for more information, check this article:http://reecon.wordpress.com/configuring-frame-relay-in-point-to-point-topology-on-cisco-ios/).

Synopsis:

What we are going to do is configure routers R1, R2 and R3 with point-to-point sub-interfaces. We will switch inverse ARP of and perform custom 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 configure remaining routers. Configuration on each router will be very similar – after enabling FR encapsulation we will specify  DLCI to IP address mapping.

Sample R2 configuration:

R2(config)#int s 1/0

R2(config-if)#encapsulation frame-relay

R2(config-if)#no ip add

R2(config-if)#no sh

R2(config)#int s 1/0.2 multipoint

R2(config-subif)#ip add 10.1.1.2 255.255.255.252

R2(config-subif)#frame-relay ip 10.1.1.1 201

R2(config-subif)#frame-relay ip 10.1.1.3 203

Now, we can examine FR map f.e on R2:

R2#show frame-relay map

Serial1/0.1 (up): ip 10.1.1.1 dlci 201(0xC9,0x3090), static,

 broadcast,

 CISCO, status defined, active

Serial1/0.1 (up): ip 10.1.1.3 dlci 203(0xCB,0x30B0), static,

 broadcast,

 CISCO, status defined, active

Configuration on R1 and R3 is similar. That’s all about Frame Relay multipoint.