Cisco Review: Basic IPv6 Address Configuration

Cisco Review: IPv6

The wide scale implementation of IPv6 is ongoing and the pace is increasing steadily. With this implementation comes a whole new addressing structure to understand and support. As of the writing of this article, almost all major Internet carriers actively support IPv6. With this, the implementation of IPv6 on all major networks (public and private) is quickly becoming required.

Over the next 10 years the phasing in of IPv6 addressing will accelerate quickly. Because of this network engineers with knowledge of IPv6 are becoming a sought after commodity. This article takes a look at the steps that are required to configure IPv6 on a Cisco router to make it reachable from neighboring devices.

The Internet Protocol (IP) version 4 was developed over 30 years ago and, at the time, provided over four billion different address combinations which seemed like an incredibly high number. However, with the wide scale explosion of Internet usage these numbers have been quickly allocated. Some of this has been mitigated by technologies like Network Address Translation (NAT) which allow multiple internal addresses to be represented with a single or a few external addresses (used on the public Internet). But regardless, the number of Internet users continues to rise exponentially requiring a solution to the addressing problem; this is where IPv6 comes in. IPv6 provides for a different addressing format which offers over three hundred and forty undecillion (3.4×1038).

One thing that can be initially confusing for those new to IPv6 is that its addressing formatting is typically represented in hexadecimal (base 16), whereas IPv4 addresses were typically represented in decimal (base 10). A common IPv4 address would look like 192.168.1.100 but a common IPv6 address would be 2000:abcd:1234:0000:0123:4567:5432:0001.

Like IPv4 addresses, IPv6 addresses are split into different networks through the use of a prefix length; a very common one seen with IPv6 is /64. When using a prefix length of /64, the first 64 bits are used to represent the network and the second 64 bits is used to represent the host portion of the network. For example, when using the /64 prefix length the IPv6 address shown above the network would be represented as 2000:abcd:1234:0000 and any combination used for the second 64 bits is considered within that network and is allocated to the hosts of that network.

With the basics out of the way, the next question is how can this actually be implemented on an actual piece of equipment (or emulated via dynamips/GNS3)? With some basic commands, a Cisco device can be connected via IPv6. These are shown below:

To configure a basic Ethernet connection between two Cisco routers the only steps that are required are to add an IPv6 address on both sides and to enable the interfaces. In this case, R1 and R2 are connected via their FastEthernet0/0 interfaces.

Configure Ethernet Connection
Figure 1

Table 1 – Basic IPv6 Interface Configuration

1 Enter privileged EXEC mode R1>enable
2 Enter global configuration mode R1#configure terminal
3 Enter interface configuration mode R1(config)#interface fastethernet0/0
4 Configure the IPv6 address R1(config-if)#ipv6 address 2000::1/64
5 Enable the interface R1(config-if)#no shutdown
6 Enter privileged EXEC mode R2>enable
7 Enter global configuration mode R2#configure terminal
8 Enter interface configuration mode R2(config)#interface fastethernet0/0
9 Configure the IPv6 address R2(config-if)#ipv6 address 2000::2/64
10 Enable the interface R2(config-if)#no shutdown

The configuration shown in Table 1 will provide for basic connectivity between R1 and R2. The next step is to configure IPv6 routing. To keep things simple Table 2 will show the configuration of a simple static route between R1 and R2.

Basic Connectivity
Figure 2

Table 2 – Simple Static Route Configuration

1 Enter privileged EXEC mode R1>enable
2 Enter global configuration mode R1#configure terminal
3 Enable IPv6 unicast routing R1(config)#ipv6 unicast-routing
4 Configure a static route for the 3000::/64 network R1(config)#ipv6 route 3000::/64 2000::2
5 Enter privileged EXEC mode R2>enable
6 Enter global configuration mode R2#configure terminal
7 Enable IPv6 unicast routing R2(config)#ipv6 unicast-routing
8 Enter interface configuration mode R2(config)#interface fa0/1
9 Configure the IPv6 address R2(config-if)#ipv6 address 3000::1/64
10 Enable the interface R2(config-if)#no shutdown

Summary

For those reading this article with some amount of Cisco experience the configuration of IPv6 is rather simple; what needs to be learned is the different IPv6 addressing concepts. For those new to the Cisco world and trying to get a handle on IPv6 implementation on a Cisco device, hopefully the contents of this article will provide enough of an understanding to test this implementation in a real or emulated environment.

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