The first step before playing with the topology is setting up the router acting as frame relay switch, this is a very straight forward process, so I will show you how to do it in a few minutes.
If you take a look at the topology you will see that R1, R4, R7 and R9 are directly connected to the Frame Relay cloud using their Serial0/0 interfaces. Behind the cloud is R3, another Cisco 3725 router like the others. Watching the corresponding sh cdp neigh we can check which router is connected to R3 serial interfaces.
R3(config-line)#do sh cdp ne Capability Codes: R - Router, T - Trans Bridge, B - Source Route Bridge S - Switch, H - Host, I - IGMP, r - Repeater Device ID Local Intrfce Holdtme Capability Platform Port ID R1 Ser 0/0 134 R S I 3725 Ser 0/0 R7 Ser 0/2 136 R S I 3725 Ser 0/0 R4 Ser 0/1 137 R S I 3725 Ser 0/0 R9 Ser 0/3 125 R S I 3725 Ser 0/0
Before start typing, we have to write down the corresponding bindings between routers and DLCIs because we will configure the router based on this table. Our table will look like this:
R1 -> DLCI 104 -> R4 R1 -> DLCI 107 -> R7 R1 -> DLCI 109 -> R9 R4 -> DLCI 401 -> R1 R4 -> DLCI 407 -> R7 R4 -> DLCI 409 -> R9 R7 -> DLCI 701 -> R1 R7 -> DLCI 704 -> R4 R7 -> DLCI 709 -> R9 R9 -> DLCI 901 -> R1 R9 -> DLCI 904 -> R4 R9 -> DLCI 907 -> R7
Once the table has been built we are ready to start configuring. The first step is enabling frame-relay switching on the router, change the encapsulation type to frame relay and declare the interfaces facing the neighbors as DCE for providing clocking.
interface Serial0/0description ToR1no ip addressencapsulation frame-relayclock rate 512000frame-relay intf-type dceinterface Serial0/1description ToR4no ip addressencapsulation frame-relayclock rate 512000frame-relay intf-type dceinterface Serial0/2description ToR7no ip addressencapsulation frame-relayclock rate 512000frame-relay intf-type dceinterface Serial0/3no ip addressencapsulation frame-relayclock rate 512000frame-relay intf-type dce
Secondly, we need to translate the mapping created in above table to a understandable IOS language. The key command for this purpose is frame relay route <input-dlci> interface <output-interface> <output-dlci> With this command we are instructing the router to do something like this: “Every frame received for this interface with input-dlci, forward to the output-interface and replace the initial-dlci with the output-dlci”.
And this results in the following output:
interface Serial0/0
description ToR1
no ip address
encapsulation frame-relay
clock rate 512000
frame-relay intf-type dce
frame-relay route 104 interface Serial0/1 401
frame-relay route 107 interface Serial0/2 701
frame-relay route 109 interface Serial0/3 901
interface Serial0/1
description ToR4
no ip address
encapsulation frame-relay
clock rate 512000
frame-relay intf-type dce
frame-relay route 401 interface Serial0/0 104
frame-relay route 407 interface Serial0/2 704
frame-relay route 409 interface Serial0/3 904
interface Serial0/2
description ToR7
no ip address
encapsulation frame-relay
clock rate 512000
frame-relay intf-type dce
frame-relay route 701 interface Serial0/0 107
frame-relay route 704 interface Serial0/1 407
frame-relay route 709 interface Serial0/3 907
interface Serial0/3
no ip address
encapsulation frame-relay
clock rate 512000
frame-relay intf-type dce
frame-relay route 901 interface Serial0/0 109
frame-relay route 904 interface Serial0/1 409
frame-relay route 907 interface Serial0/2 709
With the configuration applied on R3 and the endpoints serial interfaces with frame relay encapsulation enabled we are ready to check connectivity between them. First take a look to the R1 pvc table to find out if we are receiving the correct pvc information:
R1(config-if)#do sh fram pvc summFrame-Relay VC SummaryActive Inactive Deleted StaticLocal 2 0 0 0Switched 0 0 0 0Unused 1 0 0 0R1#sh fram pvc | i PVCPVC Statistics for interface Serial0/0 (Frame Relay DTE)DLCI = 104, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0DLCI = 107, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0DLCI = 109, DLCI USAGE = UNUSED, PVC STATUS = ACTIVE, INTERFACE = Serial0/0
Notice DLCI 109 shows as UNUSED while the other two are in LOCAL state. The reason is quite simple, based on our currently configuration, R1, R4 and R7 have an ip assigned to the serial 0/0 and inarp has run over the pvcs, changing their states. R9, however, hasn’t an ip assigned and any packet traversed the pvc yet. So let’s fix it and check that ping works.
R9(config-if)#int se0/0R9(config-if)#ip add 85.0.146.9 255.255.255.0R1#sh fram pvc | i PVCPVC Statistics for interface Serial0/0 (Frame Relay DTE)DLCI = 104, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0DLCI = 107, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0DLCI = 109, DLCI USAGE = LOCAL, PVC STATUS = ACTIVE, INTERFACE = Serial0/0R1#ping 85.0.146.4Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 85.0.146.4, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 4/28/68 msR1#ping 85.0.146.7Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 85.0.146.7, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 1/29/80 msR1#ping 85.0.146.9Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 85.0.146.9, timeout is 2 seconds:!!!!!Success rate is 100 percent (5/5), round-trip min/avg/max = 4/34/64 ms
Perfect! We succesfully configured the frame relay swith and tested end to end connectivity.
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