How to Enable IPv6 on a Cisco Router?

Cisco routers do not have Internet Protocol version 6 (IPv6) routing enabled by default. So how do we enable IPv6 on a router?

  1. First, 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.
  2. Configure the IPv6 global unicast address on an interface using the ‘ipv6 address address/prefix-length [eui-64]’ command. After you enter this command, the link local address will be automatically derived. If you omit the ‘eui-64’ parameter, you will need to configure the entire address manually.


IPv6 Configuration and Verification

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 the IP configuration and IP settings 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):
  MTU is 1500 bytes

From the output above, we can verify the following:

  1. The link local IPv6 address has been automatically configured. Link local addresses begin with FE80::/10, and the interface ID is used for the rest of the address. Because the interface’s MAC address is 00:01:42:65:3E01, the calculated address is FE80::201:42FF:FE65:3E01.IPv6 hosts check that their link local IP addresses are unique and not in use by reaching out to the local network using Neighbor Discovery Process (NDP).
  2. 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 configured on R1 (2001:0BB9:AABB:1234/64). We can test the connectivity between the devices using the ‘ping’ command 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. So that’s how to enable IPv6 on router. IPv6 addresses and the default gateway can also be configured on hosts automatically using SLAAC and DHCPv6. DNS servers are still required to be able to reach the Internet.

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