Back to Back Multilink Frame-Relay

I had this task on a recent lab. I was surprised I actually got it to work (with some help from the DocCD). Sometimes I skip these boring WAN technology tasks, but sometimes they can be fun if you get them to work :)

R6 ==== R9

R6 and R6 are connected via two serial links, serial 0/2/0 and serial 0/2/1. The task says to configure these with a /31 on the subnet 172.30.96.0 network. R6 should use DLCI 609 and R9 should use DLCI 906. Now let me say the PG was mistaken in its answer, it didn't have any frame-relay whatsoever - still waiting to hear via email what the deal was. So this is my "tentative" solution, which works great.

Here is my R6 config:

interface MFR1
ip address 172.30.96.0 255.255.255.254
no keepalive
frame-relay map ip 172.30.96.0 609
frame-relay map ip 172.30.96.1 906 broadcast
frame-relay interface-dlci 609
!
interface Serial0/2/0
no ip address
encapsulation frame-relay MFR1
clock rate 2000000
no arp frame-relay
!
interface Serial0/2/1
no ip address
encapsulation frame-relay MFR1
clock rate 2000000
no arp frame-relay

Here is the R9 config:

interface MFR1
ip address 172.30.96.1 255.255.255.254
no keepalive
frame-relay map ip 172.30.96.0 609 broadcast
frame-relay map ip 172.30.96.1 906
frame-relay interface-dlci 609
!
interface Serial0/2/0
no ip address
encapsulation frame-relay MFR1
no arp frame-relay
!
interface Serial0/2/1
no ip address
encapsulation frame-relay MFR1
no arp frame-relay

The one thing I am confused about is when the task says "R6 should use DLCI 609". I don't know whether they are referring to a global-dlci type configuration where R9 uses 609 to reach R6 or if R6 should use 609 to reach R9. Anyways, here are the points to to remember:

- Create the MFR with the the "Interface MFR 1" command first. The use the enacpsulation command on each serial interface to specify the MFR number.
- When using different DLCI's on each end, remember to map your local IP to the DLCI that the other device is using. In this case R6 needs to map it's local IP address to DLCI 609, because R9 is sending on this DLCI.
- Remember "no keepalive" on the MFR interface. Otherwise the line protocol will not come up.