Objectives–Cisco IPv4 and IPv6 Address Management
Upon completion of this chapter, you will be able to meet the following objectives:
- Describe network boundaries.
- Explain the purpose of Network Address Translation in small networks.
- Explain why IPv6 addressing will replace IPv4 addressing.
- Explain features of IPv6.
Key Terms
This chapter uses the following key terms. You can find the definitions in the Glossary.
Internet of Things (IoT) page 200
Network Address Translation (NAT) page 197
Network Address Translation 64 (NAT64) page 203
Regional Internet Registries (RIRs) page 199
Stateless Address Autoconfiguration (SLAAC) page 203
Introduction (10.0.1)
So far, we‛ve talked only about the existence of IPv4 addressing. This chapter explains how IPv4 and IPv6 will coexist in networks for some time to come. It shows you how an IPv6 address is structured and the benefits of IPv6 addressing over IPv4. But the fun part of this chapter is converting binary to hexadecimal notation. Don‛t know what hexadecimal notation is? Read on.
Network Boundaries (10.1)
Routers connect one network to another network. Only devices on separate networks need to forward their packets to a router to be able to communicate.
Video—Gateways to Other Networks (10.1.1)
Refer to the online course to view this video.
Routers as Gateways (10.1.2)
The router provides a gateway through which hosts on one network can communicate with hosts on other networks. Each interface on a router is connected to a separate network.
The IPv4 address assigned to the interface identifies which local network is connected directly to it.
Every host on a network must use the router as a gateway to other networks. Therefore, each host must know the IPv4 address of the router interface connected to the network where the host is attached. This address is known as the default gateway address. It can be either statically configured on the host or received dynamically by DHCP.
When a wireless router is configured to be a DHCP server for the local network, it automatically sends the correct interface IPv4 address to the hosts as the default gateway address. In this manner, all hosts on the network can use that IPv4 address to forward messages to hosts located at the ISP and get access to hosts on the Internet. Wireless routers are usually set to be DHCP servers by default.
The IPv4 address of that local router interface becomes the default gateway address for the host configuration. The default gateway is provided, either statically or by DHCP.
When a wireless router is configured as a DHCP server, it provides its own internal IPv4 address as the default gateway to DHCP clients. It also provides them with their respective IPv4 address and subnet mask, as shown in Figure 10-1.
Figure 10-1 A Router Serving as a Default Gateway
Routers as Boundaries Between Networks (10.1.3)
The wireless router acts as a DHCP server for all local hosts attached to it, either by Ethernet cable or wirelessly. These local hosts are referred to as being located on an internal, or inside, network. Most DHCP servers are configured to assign private addresses to the hosts on the internal network rather than Internet routable public addresses. This configuration ensures that, by default, the internal network is not directly accessible from the Internet.
The default IPv4 address configured on the local wireless router interface is usually the first host address on that network. Internal hosts must be assigned addresses within the same network as the wireless router, either statically configured, or through DHCP. When configured as a DHCP server, the wireless router provides addresses in this range. It also provides the subnet mask information and its own interface IPv4 address as the default gateway, as shown in Figure 10-2.
Figure 10-2 Default Router as Both a DHCP Server and a DHCP Client
Many ISPs also use DHCP servers to provide IPv4 addresses to the Internet side of the wireless router installed at their customer sites. The network assigned to the Internet side of the wireless router is referred to as the external, or outside, network.
When a wireless router is connected to the ISP, it acts like a DHCP client to receive the correct external network IPv4 address for the Internet interface. ISPs usually provide an Internet-routable address, which enables hosts connected to the wireless router to have access to the Internet.
The wireless router serves as the boundary between the local internal network and the external Internet.