Simple Frame-Relay Hub & Spoke Network

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Let's discuss about setting up a simple Frame-Relay Hub & Spoke network today. But before getting deep into the configuration let's first discuss about FR(Frame-Relay) hub & spoke requirements and other stuff:

Frame-Relay is a Layer 2 NBMA technology (OSI layer 2 - Data Link). That means it can only provide layer 2 connectivity between routers. Frame-Relay is basically a layer 2 WAN encapsulation just like PPP & HDLC.

Some of the FR terminologies are as mentioned below:

LMI (Local Management Interfaces) - Used between DCE and DTE, manages the connection (signaling messages, keepalive messages).

PVC (Permanent Virtual Circuit) - A predefined VC (equated to leased line)

DLCI (Data-link Connection Identifier) - Frame Relay address used in headers to identify the VC

NBMA (Non Broadcast Multi Access) - Broadcasts not supported, but more than 2 devices can be connected

To setup connectivity between two routers through FR Cloud we need L3 to L2 resolution to occur. That means a mapping/resolution is required between Local router's DLCI and remote router's ip address. This can be achieved in two ways: 1.) Using Inverse ARP 2.) Using Static FR Map Statements.

If the FR network is point to point type than we can go for Inverse ARP option but it's not recommended for Hub & Spoke topology. Now let me show you a simple Hub & Spoke Network configuration. In Hub & Spoke topology Spoke-to-Spoke traffic will always pass through Hub router. Advantage of this design is we need to buy less FR circuits from ISP as topology is not fully meshed. So setup will be cheaper. Disadvantage would be Single point of failure that means if hub router gets failed in that situation no spoke will be able to reach each other.

Config is as below:

R1#sh run int s0/0
Building configuration...

Current configuration : 219 bytes
!
interface Serial0/0
ip address 10.0.0.1 255.0.0.0
encapsulation frame-relay --> Enables Frame Relay encapsulation on WAN interface
frame-relay map ip 10.0.0.2 102 broadcast --> L2 to L3 mappings between local router's DLCI
and Remote router's ip address
frame-relay map ip 10.0.0.3 103 broadcast --> Same as mentioned in previous step
no frame-relay inverse-arp --> Disabling inverse arp as we are using Static FR maps
end

R1#sh frame-relay map
Serial0/0 (up): ip 10.0.0.2 dlci 102(0x66,0x1860), static,
broadcast,
CISCO, status defined, active
Serial0/0 (up): ip 10.0.0.3 dlci 103(0x67,0x1870), static,
broadcast,
CISCO, status defined, active



R1#sh frame-relay lmi

LMI Statistics for interface Serial0/0 (Frame Relay DTE) LMI TYPE = ANSI
Invalid Unnumbered info 0 Invalid Prot Disc 0
Invalid dummy Call Ref 0 Invalid Msg Type 0
Invalid Status Message 0 Invalid Lock Shift 0
Invalid Information ID 0 Invalid Report IE Len 0
Invalid Report Request 0 Invalid Keep IE Len 0
Num Status Enq. Sent 19 Num Status msgs Rcvd 20
Num Update Status Rcvd 0 Num Status Timeouts 0
Last Full Status Req 00:00:13 Last Full Status Rcvd 00:00:13

R2#sh run interface serial0/0
Building configuration...

Current configuration : 209 bytes
!
interface Serial0/0
ip address 10.0.0.2 255.0.0.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.0.0.1 201 broadcast
frame-relay map ip 10.0.0.3 201 --> No broadcast is included here as it's already enabled for
DLCI 201 by previous static map. So no need to enable
redundant broadcast support.
no frame-relay inverse-arp
end



R3#sh run int s0/0
Building configuration...

Current configuration : 209 bytes
!
interface Serial0/0
ip address 10.0.0.3 255.0.0.0
encapsulation frame-relay
clock rate 2000000
frame-relay map ip 10.0.0.1 301 broadcast
frame-relay map ip 10.0.0.2 301
no frame-relay inverse-arp
end


By Default we cannot ping our FR interface ip address. To make it possible we need local L2 to L3 resolution.

R1#ping 10.0.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)


R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#int s0/0
R1(config-if)#frame map ip 10.0.0.1 102 broadcast
R1(config-if)#ex
R1(config)#do ping 10.0.0.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 72/111/148 ms

Best Regards,
Deepak Arora