- Read the theory lesson below
- Read the ICND1 cram guide
As you have learned in the previous module, numerous advantages can be gained by migrating from IPv4 to IPv6. To recap, these advantages include the following:
- The simplified IPv6 packet header
- Larger address space
- IPv6 addressing hierarchy
- IPv6 extensibility
- IPv6 Broadcast elimination
- Stateless autoconfiguration
- Integrated mobility
- Integrated enhanced security
This module maps to the following CCNA syllabus requirement:
ü Describe the technological requirements for running IPv6 in conjunction with IPv4, such as dual-stack implementation
NOTE: Because the above advantages were described in detail in the previous module, they will not be described again here.
In Day 7’s lesson on IPv6, we focused exclusively on a pure IPv6 environment and learned about how IPv6 operates, as well as how the different routing protocols that support IPv6 routing are configured and validated in Cisco IOS software. While it is important to have a solid understanding of IPv6 on its own, the reality of the situation is that IPv4 is still the most predominately used version of the Internet Protocol. For this reason, it is important to understand how to integrate the two different protocol stacks when considering migrating to a pure IPv6 environment.
While migrating to an IPv6 environment would offer the previously mentioned advantages, the reality of the present situation is that not all addressable devices support IPv6, and therefore IPv4 and IPv6 must coexist within the same network for devices running different protocol stacks in order to use the same network infrastructure. IPv4 and IPv6 integration and coexistence strategies are divided into three broad classes, as follows:
- Dual-stack implementation
- Tunnelling
- Protocol translation
Dual-stack implementation is required when internetwork devices and hosts use both protocol stacks (i.e., IPv4 and IPv6) at the same time. Dual-stack implementation allows the hosts to use either IPv4 or IPv6 to establish end-to-end IP sessions with other hosts.
NOTE: Dual-stack implementation does not mean that the IPv4-only and IPv6-only hosts have the ability to communicate with each other. To do so, additional protocols and mechanisms are needed. Dual-stack simply means that the hosts (and infrastructure) are able to support both the IPv4 protocol stack and the IPv6 protocol stack.
In situations where dual-stack implementation cannot be used, it is possible to tunnel the IPv6 packets over IPv4 networks. In these implementations, tunnels are used to encapsulate IPv6 packets in IPv4 packets, allowing them to be sent across portions of the network that don’t have or do not yet natively support IPv6. This allows the IPv6 “islands” to communicate over the underlying IPv4 infrastructure.
NOTE: With tunnelling, nodes or internetwork devices must support dual-stack in order to tunnel the IPv6 packets over the IPv4 infrastructure.
Finally, in some cases, it is possible that IPv4-only environments will need to communicate with IPv6-only environments, and vice versa. In these situations, neither dual-stack nor tunnelling implementations can be used so protocol translation between IPv4 and IPv6 must be enabled. While supported, this is the least desirable method of integrating IPv4 and IPv6 networks. However, because it is supported, it is important to understand how to do this.
The remainder of this module will describe, in detail, the dual-stack implementation and tunnelling methods of integrating IPv4 and IPv6 networks. Included are configuration examples specific to Cisco IOS software.