There are several popular mechanisms which can allocate an IP address to a computer or network device, however DHCP is probably the most advanced method in common use.    It’s a robust and efficient protocol which uses UDP as it’s transport mechanism.   It exists largely as a result of the shortcomings of it’s predecessor BOOTP to which DHCP offers a host of enhancements.

One of the biggest improvements was that a DHCP allows the inclusion of a client’s subnet mask, which allows clients to be configured much easily particularly on large networks with many subnets.  The other addition was regarding the ability to lease IP addresses for a specified period.  In large networks this is crucial because of several reasons but primarily it made managing IP addresses much simpler and ensured that IP addresses weren’t locked into computers which weren’t even switched on.   It enabled a network administrator to work with a much smaller pool of usable IP addresses than the number of ‘potential’ network enabled clients.

Although DHCP is a huge improvement on the IP addressing allocations systems that preceded it, there is still some situations which can cause problems.  It’s worth considering issues with DHCP if there are network connectivity problems with your clients.

Typically DHCP related problems are to do with configuration or connectivity.  One of the simplest issues is that DHCP hasn’t actually been configured on a client, although most later versions of Windows attempt to use DHCP by default some older versions need the IP address mechanism configured first.

A DHCP server will often be on a different network segment that the client it is attempting to update, any issues of connectivity between the two segments will be made worse if IP addresses are not allocated by the DHCP server.   Remember the protocol uses UDP as it’s transport mechanism which does not have any delivery checking.   A client will also broadcast attempting to find the nearest connectible DHCP server, this can cause issues if these broadcasts are not repeated by some network hardware.

If you do have problems on larger networks with DHCP broadcasts not being repeated then you should configure IP helper addresses on routers within the network to solve this.  Sometimes it can get confusing with multiple DHCP servers on different networks, it’s important you have a good VPN service in order to connect to the various devices to ensure connectivity across segments.

If  you’ve ruled out connectivity problems make sure the DHCP server is configured properly and has plenty of available IP addresses to allocate.  Sometimes problems are not that the DHCP can’t be contacted but has simply run out of addresses to allocate to clients.

With Thanks

Raphael Silvano – Italian Networks, Rai Streaming Estero, 2017 Haver Press

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