Split horizon

Now Lets look only on Router R1,R2 and R3

We know it’s a full mess topology. Hence R2 and R3 updates are directly exchanged via DLCI 203 and 302

Lets verify it!!!!

R3#ping 150.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 150.2.2.2, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 16/58/96 ms

R3#traceroute 150.2.2.2

Type escape sequence to abort.

Tracing the route to 150.2.2.2

  1 155.1.123.2 84 msec *  104 msec

We have the reachability Now make this full mess as hub and spoke topology.

As can't remove the DLCI its under SP so what shall we do hmmmm!!!!!!

Yeah rite we can disable the invarp for particular DLCI 203 and 302

R2#sh run

interface Serial0/0

 ip address 155.1.123.2 255.255.255.0

 encapsulation frame-relay

 serial restart-delay 0

 no frame-relay inverse-arp IP 203

end

R3#sh run int s0/0

interface Serial0/0

 ip address 155.1.123.3 255.255.255.0

 encapsulation frame-relay

 serial restart-delay 0

 no frame-relay inverse-arp IP 302

end

Now check the reachability on R2 and R3.

R2#ping 150.3.3.3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 150.3.3.3, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

Interesting uh?? So this make a issues what you think what the issues will be.

Correct!!! Its Split Horizon

To overcome this solution we can disable the split horizon on Hub(R1)

R1#sh run int s0/0.123

interface Serial0/0.123 multipoint

 ip address 155.1.123.1 255.255.255.0

 no ip split-horizon eigrp 100

 frame-relay interface-dlci 102

 frame-relay interface-dlci 103

end

Yep now we have disabled the split horizon. Lets take a look on R2 routing table

R2#sh ip route

     150.3.0.0/24 is subnetted, 1 subnets

D       150.3.3.0 [90/2809856] via 155.1.123.1, 00:03:30, Serial0/0

R3#sh ip route

     150.2.0.0/24 is subnetted, 1 subnets

D       150.2.2.0 [90/2809856] via 155.1.123.1, 00:03:58, Serial0/0

We got the updates from R2 and R3 via R1. Now lets try to pass the traffic

R3#ping 150.2.2.2

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 150.2.2.2, timeout is 2 seconds:

.....

Success rate is 0 percent (0/5)

We have the update but what we don't have is DLCI mapping to forward traffic to 150.2.2.2

R3#sh frame-relay map

Serial0/0 (up): ip 155.1.123.1 dlci 301(0x12D,0x48D0), dynamic,

              broadcast,

              CISCO, status defined, active