We are going to build our first IPv6 network. We will configure first two routers and then we will connect a host to C00 and test network connectivity. Although we do not need so many hosts we will use a 112 netmask for simplicity. This way we will have to care only on the last block of the IPv6 address.



|| Router || Interface || IP ||
| C00 | Fa0/0 | 2001:DB8::1/112 |
| C00 | Fa0/1 | 2001:DB8::1:1/112 |
| C01 | Fa0/0 | 2001:DB8::2/112 |
| Host | Fa0/0 | 2001:DB8::1:2/112 |

Although the host is represented by a router we will use it only to test connectivity. First, we will configure the devices, do not forget to enable the interfaces!. On C00:

C00(config)#int Fa0/0
C00(config-if)#ipv6 address 2001:DB8::1/112
C00(config-if)#int Fa0/1
C00(config-if)#ipv6 address 2001:DB8::1:1/112

On C01:

C01(config-if)#int Fa0/0
C01(config-if)#ipv6 address 2001:DB8::2/112

Finally, on the Host:

Host(config)#int Fa0/0
Host(config-if)#ipv6 address 2001:DB8::1:2/112

Let's try to ping from C00 both C01 and the Host:

C00#ping 2001:DB8::2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/11/24 ms

C00#ping 2001:DB8::1:2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8::1:2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 4/5/8 ms

Let's see, however, what happens if we ping C00 and C01 from Host. We will add first a static network on Host to reach the network 2001:DB8::0/112 through the IP 2001:DB8::1:1 and a route back to the host on C01 using C00 as a next-hop:

C01#conf t
Enter configuration commands, one per line. End with CNTL/Z.
C01(config)#ipv6 route 2001:DB8::1:0/112 2001:DB8::1
C01(config)#end

Host#conf t
Enter configuration commands, one per line. End with CNTL/Z.
Host(config)#ipv6 route 2001:DB8::0/112 2001:DB8::1:1
Host(config)#end
Host#ping 2001:DB8::1:1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8::1:1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 0/5/12 ms
Host#ping 2001:DB8::2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8::2, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
Host#

It seems we can not ping C01 using C00 as a router, let's debug ipv6 packets on C00:

C00# debug ipv6 packets
*Mar 1 00:36:35.407: IPV6: source FE80::C604:57FF:FE97:1 (local)
*Mar 1 00:36:35.407: dest FE80::C60A:57FF:FE97:0 (FastEthernet0/1)
*Mar 1 00:36:35.407: traffic class 224, flow 0x0, len 72+8, prot 58, hops 255, originating
*Mar 1 00:36:35.407: IPv6: Sending on FastEthernet0/1
*Mar 1 00:36:35.411: IPV6: source FE80::C60A:57FF:FE97:0 (FastEthernet0/1)
*Mar 1 00:36:35.411: dest FE80::C604:57FF:FE97:1
*Mar 1 00:36:35.411: traffic class 224, flow 0x0, len 64+14, prot 58, hops 255, forward to ulp
*Mar 1 00:36:36.919: IPV6: source 2001:DB8::1:2 (FastEthernet0/1)
*Mar 1 00:36:36.919: dest 2001:DB8::2 (FastEthernet0/0)
*Mar 1 00:36:36.919: traffic class 0, flow 0x0, len 100+14, prot 58, hops 64, not a router?
*Mar 1 00:36:38.923: IPV6: source 2001:DB8::1:2 (FastEthernet0/1)
*Mar 1 00:36:38.923: dest 2001:DB8::2 (FastEthernet0/0)
*Mar 1 00:36:38.923: traffic class 0, flow 0x0, len 100+14, prot 58, hops 64, not a router?
*Mar 1 00:36:40.919: IPV6: source 2001:DB8::1:2 (FastEthernet0/1)
*Mar 1 00:36:40.919: dest 2001:DB8::2 (FastEthernet0/0)
*Mar 1 00:36:40.919: traffic class 0, flow 0x0, len 100+14, prot 58, hops 64, not a router?
*Mar 1 00:36:42.923: IPV6: source 2001:DB8::1:2 (FastEthernet0/1)
*Mar 1 00:36:42.923: dest 2001:DB8::2 (FastEthernet0/0)
*Mar 1 00:36:42.923: traffic class 0, flow 0x0, len 100+14, prot 58, hops 64, not a router?
*Mar 1 00:36:44.919: IPV6: source 2001:DB8::1:2 (FastEthernet0/1)
*Mar 1 00:36:44.919: dest 2001:DB8::2 (FastEthernet0/0)
*Mar 1 00:36:44.919: traffic class 0, flow 0x0, len 100+14, prot 58, hops 64, not a router?

Not a router? We have to enavle 'ipv6 unicast-routing' just like in the old days. Let's do it and try again:

C00(config)#ipv6 unicast-routing

C01(config)#ipv6 unicast-routing

Host#ping 2001:DB8::2

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 2001:DB8::2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 8/13/24 ms

If you were still debugging ipv6 packets when you enabled the ipv6 routing you could see that the router started advertising itself as a router on the local-link network:

*Mar 1 00:39:04.103: IPv6: Sending on FastEthernet0/0
*Mar 1 00:39:04.103: IPV6: source FE80::C604:57FF:FE97:1 (local)
*Mar 1 00:39:04.103: dest FF02::1 (FastEthernet0/1)
*Mar 1 00:39:04.103: traffic class 224, flow 0x0, len 104+1396, prot 58, hops 255, originating
*Mar 1 00:39:04.103: IPv6: Sending on FastEthernet0/1
*Mar 1 00:39:08.271: IPV6: source FE80::C604:57FF:FE97:0 (local)
*Mar 1 00:39:08.271: dest FF02::1 (FastEthernet0/0)
*Mar 1 00:39:08.271: traffic class 224, flow 0x0, len 104+1396, prot 58, hops 255, originating

We will talk about this later on another post.

So, we already built our first IPv6 network. On future posts we will continue growing this network adding a more of functionalities and testing capabilities.