Cisco routers do not have IPv6 routing enabled by default. To configure IPv6 on a Cisco routers, you need to do two things:
- enable IPv6 routing on a Cisco router using the ipv6 unicast-routing global configuration command. This command globally enables IPv6 and must be the first command executed on the router.
- configure the IPv6 global unicast address on an interface using the ipv6 address address/prefix-length [eui-64] command. If you omit omit the eui-64 parameter, you will need to configure the entire address manually. After you enter this command, the link local address will be automatically derived.
Here is an IPv6 configuration example:
R1(config)#ipv6 unicast-routing R1(config)#int Gi0/0 R1(config-if)#ipv6 address 2001:0BB9:AABB:1234::/64 eui-64
We can verify that the IPv6 address has been configured by using the show ipv6 interface Gi0/0 command:
R1#show ipv6 interface Gi0/0 GigabitEthernet0/0 is up, line protocol is up IPv6 is enabled, link-local address is FE80::201:42FF:FE65:3E01 No Virtual link-local address(es): Global unicast address(es): 2001:BB9:AABB:1234:201:42FF:FE65:3E01, subnet is 2001:BB9:AABB:1234::/64 [EUI] Joined group address(es): FF02::1 FF02::2 FF02::1:FF65:3E01 MTU is 1500 bytes ....
From the output above we can verify two things:
- the link local IPv6 address has been automatically configured. Link local IP addresses begin with FE80::/10 and the interface ID is used for the rest of the address. Because the MAC address of the interface is 00:01:42:65:3E01, the calculated address is FE80::201:42FF:FE65:3E01.
- the global IPv6 address has been created using the modified EUI-64 method. Remember that IPv6 global addresses begin with 2000::/3. So in our case, the IPv6 global address is 2001:BB9:AABB:1234:201:42FF:FE65:3E01.
We will also create an IPv6 address on another router. This time we will enter the whole address:
R2(config-if)#ipv6 address 2001:0BB9:AABB:1234:1111:2222:3333:4444/64
Notice that the IPv6 address is in the same subnet as the one configured on R1 (2001:0BB9:AABB:1234/64). We can test the connectivity between the devices using ping for IPv6:
R1#ping ipv6 2001:0BB9:AABB:1234:1111:2222:3333:4444 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 2001:0BB9:AABB:1234:1111:2222:3333:4444, timeout is 2 seconds: !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 0/0/0 ms
As you can see from the output above, the devices can communicate with each other.