Image of Cortney & Jeremy

Configuring Frame-Relay, Part 3

by Jeremy L. Gaddis on July 7, 2009 · 2 comments

in Networking

Okay, after much delay here’s part 3 of the “Configuring Frame-Relay” series. In part 3, we’ll combine what we’ve learned from part one and part two and work with this topology:

As you can see from the diagram, we’ll be using the physical serial 0/0 interfaces to connect R1, R2, and R3. In addition, we’ve added a new router, R4, to the diagram. R1 and R4 will be connected over a point-to-point subinterface (serial 0/0.14). The purpose of this part three is to show how we can use both the physical interface and a point-to-point subinterface at the same time (we could also add a point-to-multipoint subinterface if we wanted, but we’ll save that for later).

The initial configurations for R1, R2, and R3 will be identical to what we saw in part one. If you haven’t already viewed the video in part one, I recommend you do that now.

For the sake of completeness, here are the initial configurations for the hub-and-spoke portion of our frame relay network:

R1# configure terminal
R1(config)# interface serial 0/0
R1(config-if)# encapsulation frame-relay
R1(config-if)# no frame-relay inverse-arp
R1(config-if)# ip address 172.16.123.1 255.255.255.0
R1(config-if)# frame-relay map ip 172.16.123.2 102 broadcast
R1(config-if)# frame-relay map ip 172.16.123.3 103 broadcast
R1(config-if)# no shutdown
R2# configure terminal
R2(config)# interface serial 0/0
R2(config-if)# encapsulation frame-relay
R2(config-if)# no frame-relay inverse-arp
R2(config-if)# ip address 172.16.123.2 255.255.255.0
R2(config-if)# frame-relay map ip 172.16.123.1 201 broadcast
R2(config-if)# frame-relay map ip 172.16.123.3 201
R2(config-if)# no shutdown
R3# configure terminal
R3(config)# interface serial 0/0
R3(config-if)# encapsulation frame-relay
R3(config-if)# no frame-relay inverse-arp
R3(config-if)# ip address 172.16.123.3 255.255.255.0
R3(config-if)# frame-relay map ip 172.16.123.1 301 broadcast
R3(config-if)# frame-relay map ip 172.16.123.2 301
R3(config-if)# no shutdown

With this portion up and running (make sure to verify reachability!), we can get to work bringing up the point-to-point connection between R1 and R4. Let’s start with R1. The encapsulation on the physical interface is already configured, so we can skip that part and jump straight in:

R1(config-if)# interface serial 0/0.14 point-to-point
R1(config-subif)# frame-relay interface-dlci 104
R1(config-fr-dlci)# ip address 172.16.14.1 255.255.255.0

Easy enough, right? Now let’s set up R4:

R4# configure terminal
R4(config)# interface serial 0/0
R4(config-if)# encapsulation frame-relay
R4(config-if)# no shutdown
R4(config-if)# interface serial 0/0.14 point-to-point
R4(config-subif)# frame-relay interface-dlci 401
R4(config-fr-dlci)# ip address 172.16.14.4 255.255.255.0

Since we’ve already saw the video in part two, this is a piece of cake as well. At this point, we should be able to ping R1 from R4 and vice versa. Verify:

R4(config-subif)# do ping 172.16.14.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.14.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms
R1(config-subif)# do ping 172.16.14.4

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 172.16.14.4, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms

Success! Our configuration is now complete. Here’s what the routing table looks like on R1:

R1(config-subif)# do show ip route | begin Gateway
Gateway of last resort is not set

     172.16.0.0/24 is subnetted, 2 subnets
C       172.16.14.0 is directly connected, Serial0/0.14
C       172.16.123.0 is directly connected, Serial0/0

Note that we don’t have “full reachability”, however. While R1 can talk to all the other routers, R2 and R3 and effectively segmented from R4 — they don’t have a route back and forth. We’ll address that in part four, where we’ll continue on and configure OSPF throughout our frame-relay network.

Here, for your viewing pleasure, is a video walking through the complete configuration from start to finish (without narration this time):

{ 2 comments… read them below or add one }

Tim December 11, 2012 at 7:00 pm

Chris, love your site, hopefully you still monitor the ‘ask’ section; I have two questions for you:
Why config ppp over top of frame encapsulation? Security reasons?
Also, why is the ‘broadcast’ command not required when using frame relay with P2P links? Thanks man!

Reply

Tim December 11, 2012 at 7:10 pm

Jeremy, (a.k.a Chris), I don’t know why the hell I called you Chris, but I still love your website man, sorry about that :/

Reply

Leave a Comment

Previous post:

Next post: