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Table Of Contents  The TCP/IP Guide
 9  TCP/IP Lower-Layer (Interface, Internet and Transport) Protocols (OSI Layers 2, 3 and 4)
      9  TCP/IP Internet Layer (OSI Network Layer) Protocols
           9  Internet Protocol (IP/IPv4, IPng/IPv6) and IP-Related Protocols (IP NAT, IPSec, Mobile IP)
                9  Internet Protocol Version 4 (IP, IPv4)
                     9  IP Addressing
                          9  IP Addressing Concepts and Issues

Previous Topic/Section
IP Addressing Categories (Classful, Subnetted and Classless) and IP Address Adjuncts (Subnet Mask and Default Gateway)
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1
2
Next Page
IP Address Management and Assignment Methods and Authorities
Next Topic/Section

Number of IP Addresses and Multihoming
(Page 1 of 2)

Each network interface on an IP internetwork has a separate IP address. In a classical network, each regular computer, usually called a host, attaches to the network in exactly only one place, so it will have only one IP address. This is what most of us are familiar with when using an IP network (and is also why most people use the term “host” when they really mean “network interface”.)

If a device has more than one interface to the internetwork, it will have more than one IP address. The most obvious case where this occurs is with routers, which connect together different networks and thus must have an IP address for the interface on each one. It is also possible for hosts to have more than one IP address, however. Such a device is sometimes said to be multihomed.

Multihoming Methods

There are two ways that a host can be multihomed:

  • Two Or More Interfaces To The Same Network: Devices such as servers or high-powered workstations may be equipped with two physical interfaces to the same network for performance and/or reliability reasons. They will have two IP addresses on the same network with the same network ID.

  • Interfaces To Two Or More Different Networks: Devices may have multiple interfaces to different networks. The IP addresses will typically have different network IDs in them.

Figure 59 shows examples of both types of multihomed device. Of course, these could be combined, with a host having two connections to one network and a third to another network. There are also some other “special cases”, such as a host with a single network connection having multiple IP address aliases.


Figure 59: Multihomed Devices On An IP Internetwork

This internetwork consists of two LANs, A (shown in purple) and B (shown in blue). LAN A has a multihomed workstation, shown with two IP network interface “circles”. The two LANs are connected together through a multihomed, shared server, that has been configured to route traffic between them. Note that this server also handles all traffic passing between LAN B and the Internet (since the Internet connection is in LAN A only.)

 


Note: When subnetting is used the same distinction can be made between multihoming to the same subnet or a different subnet.



Previous Topic/Section
IP Addressing Categories (Classful, Subnetted and Classless) and IP Address Adjuncts (Subnet Mask and Default Gateway)
Previous Page
Pages in Current Topic/Section
1
2
Next Page
IP Address Management and Assignment Methods and Authorities
Next Topic/Section

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Version 3.0 - Version Date: September 20, 2005

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