 Hello
Readers!
If you're using static IP assignments, then you know there are drawbacks. A user
picks up his PC and walks to another part of the building, and suddenly you have
a connectivity problem. Users set up their own servers without your knowledge,
and introduce all kinds of security issues.
Tired of stamping out fires one by one because of static addresses? Then you need
to look into dynamic IPs. Dynamic IPs are more "economical" in many ways. You'll
save headaches by dynamically assigning addresses, plus you won't need as many
addresses if you have lots of users on the go. Terry Dawson clues you in on the
many ways you can benefit in the following article. Read on to find out more about
the options open to you.
Do you have any tips on assigning dynamic IPs or on any other topic that other
sys admins might like to read? Go ahead and send them along! Also encouraged are
sys admin "war stories." If you've been a systems administrator for any length
of time at all you can probably fill a book. I’ll publish them here, give you
credit (unless you want to stay anonymous), and even give you a little plug for
your business. Send your comments, quips, tips and stories to jackie@sysadminnews.com.
Dynamic Address Assignment
By Terry Dawson
In many networks, IP addresses are manually assigned to hosts. There are a number
of reasons why for most hosts this is an unnecessary and even undesirable arrangement.
In this column we'll describe how to manage the automatic allocation of IP
addresses (and other useful information) in a Linux environment for hosts connected
to a broadcast-style network like Ethernet. For convenience, we'll refer to these
networks as Ethernet, but the same principles apply to many different types of
underlying protocols such as FDDI, Token Ring, and AX.25.
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What advantages does dynamic assignment offer?
There are a number of situations where dynamic IP address assignment provides
benefit. Some of the more important of these are:
- Diskless workstations
- This was the application that generated the first standard implementations
of dynamic IP address assignment. Diskless workstations typically have no stored
configuration data. Instead, when they are booted they request configuration data
from their network connection. One very important configuration item is the IP
address they should use in order to download their operating system.
- Itinerant hosts
- If you're a laptop owner, you'll understand the nuisance it is to have to
manually reconfigure your network configuration every time you move, for example,
from your docking station at home, to your GPRS-based mobile telephone while traveling
to your docking station at work. Dynamic address assignment automates the low-level
network configuration for you when you connect to each new network.
- Allows "overbooking" of IP address space
- IP addresses are a scarce resource. If you have a number of potential hosts
on your network, but an actual occupancy rate that is significantly lower than
the total, dynamic assignment allows you to efficiently manage the number of IP
addresses required to support large numbers of potential hosts. Internet service
providers routinely support quite large numbers of customer on pools of IP addresses
that are quite small, this is sometimes called "overbooking." Dial-up modem, ADSL,
and cable modem technologies are prime examples of network technologies that typically
exploit this mechanism.
- Reduces documentation and duplicates IP address clashes
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- Manually and statically assigning IP addresses to hosts requires accurate
and up-to-date documentation in order to prevent duplicate IP address problems.
Nearly all dynamic address assignment systems provide logging and reporting capabilities
that make the IP address assignment process largely self-documenting.
- Reduces user-induced faults
- In office environments, it is common to have more than one IP network supporting
the user desktop computers. It is common for users to move from desk to desk and
often they will consider it reasonable to move their computer with them when they
do. Unfortunately if they happen to move from one Ethernet port supporting one
IP network on one desk, to another identical-looking Ethernet port supporting
another IP network their computer will require reconfiguration to work. Inevitably
this results in a call to the IT help-desk wanting someone to "come fix my PC."
Dynamic IP address assignment handles this situation elegantly by providing them
with a new address from their new network when they first boot up, completely
avoiding the manual intervention required to get them working at their new desk.
- Discourages inappropriate configuration of servers
- Dynamic address assignment can help to discourage inappropriate configuration
of some types of application servers on user desktop computers. Most application
servers require the end-user to know the IP address of the server machine in order
to connect, having the IP address change periodically on user desktop computers
frustrates attempts to run those types of servers on them. It's important to note
that it's only a frustration and not an insurmountable problem. Dynamic DNS server
technology exists specifically to overcome this problem, and some application
servers use directory services or other mechanisms to advertise their presence
and at what address they're available. Their IP address then becomes largely irrelevant.
Read
more Here
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