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Routing to Mobile Hosts (Mobile IP)
Course: Systems Programming (01:198:214)
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University: Rutgers University
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Routing to Mobile Hosts (Mobile IP)
It appears in many different places that IP addresses don't change. Transport protocols
functioning in a mobile world, for instance, require some re-evaluation of the assumption that the
IP address would remain constant for the duration of a connection, as we'll see in the following
chapter. It is important to note that routers can also relocate, even if moving endpoints are
something we are all familiar with. Although endpoint mobility is already more prevalent, there
are still many situations where a mobile router might be useful. An emergency response team
setting up a network after a natural disaster has destroyed all the fixed infrastructure is one
instance that comes to mind. Support for mobility poses challenges with incremental rollout, as is
the case with many technologies. It's reasonable to anticipate that there will be many routers and
hosts around for the foreseeable future that make that assumption given that the Internet's first
two decades were exclusively made up of nodes that didn't migrate. As a result, solutions for
mobility must handle gradual deployment.
In contrast, IP version 6 was able to incorporate mobility into its design from the start, giving it
considerable advantages. A few clarifications are necessary before we look at some of the
methods for supporting mobile devices. People frequently conflate mobility with wireless
networks. After all, for obvious reasons, wireless and mobility are frequently seen together.
Mobility, on the other hand, deals with what occurs when a node moves around as it
communicates, whereas wireless communication is actually about transferring data from point A
to point B without a cable, as explored in some depth in Chapter 2. Undoubtedly, a lot of nodes
that use wireless communication channels are stationary, and stationary nodes occasionally
employ wired connection with mobile nodes (although this is less common). Finally, what we
can refer to as network-layer mobility is the main focus of this chapter.
In other words, we want to know how to handle nodes that switch between networks. However,
in large heterogeneous systems like the Internet, we need to support mobility more broadly
across networks. As we saw in Section 2.7, moving from one access point to another within the
same 802.11 network can be handled by mechanisms specific to 802.11, and cellular telephone
networks also have ways to handle mobility, of course. The main method used in the current
Internet architecture to address the issue of packet routing to mobile hosts is mobile IP. Although
it adds a few new features, it does not necessitate any modifications from non-mobile hosts or
the majority of routers, solving the incremental deployment problem mentioned before. It is
expected that the mobile host has a fixed IP address, also known as its home address, with a
network prefix identical to that of its home network. Since it doesn't change, long-lived
applications can use it as the mobile host roams.
This is the address that other hosts will use when they first transmit packets to the mobile host.
This can be regarded as the host's persistent identifier. This address will change every time the
host roams to a new network, so we can think of it as being more like the host's locator.
However, it is important to note that the host does not lose its permanent home address when it
acquires a new address on the foreign network. As we'll see later, this home address is essential
to its capacity to maintain communications when it's moving. Agent advertisement messages are
used by both domestic and foreign agents to periodically make their presence known on the
