Advance WAN Configuration, Frame Relay

While preparing for my CCIE (Routing & Switching), I am going through the detail concept of each topic, lets talk little bit about frame relay. The different terminology that are used in frame realy are as under:

Terminlogy

Permanent Virtual Circuti (PVC)
Data-Link Connection Identifier (DLCI)
Local Management Interface (LMI)
Network-to-Network Interface (NNI)
Local Access Rate / Committed Information Rate

Configuration

Base Config, W/Inverse-ARP
Manual Config, Sub-Interfaces
Hybrid Config Example
Verification
Frame-Relay Config, W/Inverse ARP

What this Inverse-ARP means, when Router-A sends request with DLCI 102 so the response of Router-B is positve that I available here so this response of Router-B is Inverse-ARP. Whenever configuration of frame relay is done so we can have any one of the following state by issuing a single command:

Router-B # Show frame-relay map

Status:

Active: This means that Local and Remote connection are working
InActive: This means that Local Connection is woring while Remote is not working
Deleted: Local Connection is not working while Remote is unknown
Let suppose Router-A say to Router-B that I want to reach DLCI 109 and in response Router-B say I am unaware of this DLCI so this is Deleted Status.
Lets look at the output on one router

Router-C#show frame-relay map

Serial1/0 (up): ip 172.16.1.3 dlci 301(0x12D,0x48D0), static,
broadcast,
CISCO, status defined, active
Serial1/0 (up): ip 172.16.1.1 dlci 301(0x12D,0x48D0), static,
broadcast,
CISCO, status defined, active

NOTE: In CCIE Lab and actual lab we have to turn off this INVERSE-ARP as it will dynamically find the DLCI and Traffice will send to those route to which we don’t want to send.

Frame Relay Configuration, Sub Interfaces

First Let me clear why we using sub-interfaces, why not single interfaces so there are couple of reason for it, 1st Reason is that we have two different subnets, 2nd Reason is Due to Split Horizon (“It states that don’t send traffic back on interface on which it arrives” for further deatil see Here), 3rd Reason is that look at the topology when LAN traffic of Router-B send to Router-A so it will send to Router-C and Routing loops will be created and split-horizon rules tells us not to do this, so we use sub-interfaces for this reason.


Look at the configuration below, but let me explain two commands that why I used that here:

Router-A (config) # interface serial 1/0
Router-A (config-if) # no frame-relay inverse-arp

We block to discover who is on other side

Router-A (config-if) # no arp frame-relay

This command states that one any onw try to access you, so don’t response
After configuration between Router-A and Router-B as Point-to-Point and Router-A and Router-C, Router-D as Multipoint so when we chek connectivity between Router-C and Router-D so it will not work as we have to do the DLCI mapping for them also.
Another most important thing is that at end of all configuraion The Router-D LAN traffice will be there in Router-A but not in Router-B and Router-C and it is because of split-horizon, so we have to turn off it manually (Traffice send from Router-D on interface serial 1/0.2)

Router-A(config)# interface serial 1/0.2
Router-A(config-subif)# no ip split-horizon eigrp 1

Router-C # show ip route

172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
D 172.16.0.0/16 is a summary, 00:01:12, Null0
C 172.16.1.0/24 is directly connected, Serial1/0
D 10.0.0.0/8 [90/2681856] via 172.16.1.1, 00:00:12, Serial1/0
C 192.168.2.0/24 is directly connected, FastEthernet2/0
D 192.168.3.0/24 [90/2684416] via 172.16.1.1, 00:00:07, Serial1/0
The Router-D LAN route is shown as bold in the output.

Now lets look at the detail configuration on each router:

Frame-Relay Switch

hostname FRS
!
boot-start-marker
boot-end-marker
!

ip cef
!
frame-relay switching
!
interface FastEthernet0/0
no ip address
shutdown
duplex half
!
interface Serial1/0
no ip address
encapsulation frame-relay
serial restart-delay 0
clock rate 64000
no fair-queue
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 102 interface Serial1/1 201
frame-relay route 103 interface Serial1/2 301
frame-relay route 104 interface Serial1/3 401
!
interface Serial1/1
no ip address
encapsulation frame-relay
serial restart-delay 0
clock rate 64000
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 201 interface Serial1/0 102
!
interface Serial1/2
no ip address
encapsulation frame-relay
serial restart-delay 0
clock rate 64000
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 301 interface Serial1/0 103
!
interface Serial1/3
no ip address
encapsulation frame-relay
serial restart-delay 0
clock rate 64000
frame-relay lmi-type cisco
frame-relay intf-type dce
frame-relay route 401 interface Serial1/0 104
!

Router-A CONFIGURATIONS
!
hostname A
!
ip cef
!
interface Serial1/0
no ip address
encapsulation frame-relay
serial restart-delay 0
no fair-queue
no arp frame-relay
no frame-relay inverse-arp
!
interface Serial1/0.1 point-to-point
ip address 10.1.1.1 255.255.255.0
frame-relay interface-dlci 102
!
interface Serial1/0.2 multipoint
ip address 172.16.1.1 255.255.255.0
no ip split-horizon eigrp 1
frame-relay map ip 172.16.1.3 104 broadcast
frame-relay map ip 172.16.1.2 103 broadcast
!
router eigrp 1
network 10.0.0.0
network 172.16.0.0
auto-summary
!

Router-C CONFIGURATIONS
!
hostname C
!
no aaa new-model
!
!
ip cef

interface Serial1/0
ip address 172.16.1.2 255.255.255.0
encapsulation frame-relay
serial restart-delay 0
clock rate 64000
no arp frame-relay
frame-relay map ip 172.16.1.3 301 broadcast
frame-relay map ip 172.16.1.1 301 broadcast
no frame-relay inverse-arp
frame-relay lmi-type cisco
!
interface FastEthernet2/0
ip address 192.168.2.1 255.255.255.0
duplex auto
speed auto
!
router eigrp 1
network 172.16.0.0
network 192.168.2.0
auto-summary
!

I Hope this will be informative for You !

Cheers :)