To begin with I check my routing table on R0.
R0#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.1.0/30 is subnetted, 1 subnets
C 192.168.1.0 is directly connected, Serial1/0
Currently I can only see directly connected interfaces. Without any static routes or routing protocols traffic from one network cannot reach the other.
R0#ping 192.168.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/11/24 ms
R0#ping 192.168.1.5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.5, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
I can ping the R1 interface on my network but not the interface on the other network. This is because R0 does not know where 192.168.1.5 is. By creating a static route I tell R0 which interface to send packets out of.
R0(config)#ip route 192.168.1.4 255.255.255.252 192.168.1.3
R0(config)#end
Now when I examine the route table I can see the static route I have created.
R0#sh ip route
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2
i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
ia - IS-IS inter area, * - candidate default, U - per-user static route
o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial1/0
S 192.168.1.4 [1/0] via 192.168.1.3
Now If I attempt to ping the ethernet interface on R1 I get a response.
R0#ping 192.168.1.5
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.5, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/6/8 ms
So what about R2?
R0#ping 192.168.1.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.6, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Well R2 is receiving the ICMP ping packets but it doesn't know how to get them back to me. By going to R2 and giving it a route to get back it will know which direction to send packets back.
R2#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R2(config)#ip route 192.168.1.0 255.255.255.252 192.168.1.4
Because R1 know which networks it is directly connect to it happily passes the packets to the correct interface.
R1#sh ip route connected
192.168.1.0/30 is subnetted, 2 subnets
C 192.168.1.0 is directly connected, Serial0/0
C 192.168.1.4 is directly connected, Ethernet1/0
Attempting to ping R2 from R0 now produces the desired result.
R0#ping 192.168.1.6
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.1.6, timeout is 2 seconds:
.!!!!
Success rate is 80 percent (4/5), round-trip min/avg/max = 4/12/24 ms
