DNS and DHCP

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Hi guys,

Can anyone help me get a better understanding of these two? i have only a really basic understanding of the two (ie DHCP assigns IP addresses and sets the default gateway and DNS is, i believe, supposed to be use for when you ask for a connection to 'pc1', in that it converts the name into the IP for the machine in question.... i think), and im aware that they must interact with each other, but i really dont think i have a clear picture of the two.

Thanks
Fergal

 

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You pretty much have it right. However - they don't interact with each other, and either might not be present (although the lack of DNS would be a pain to human users!).

The only thing I would add is that DHCP is basicaly an Ethernet (and related protocols) based thing, so it's use is confined to the local physical network, whereas DNS is an IP based thing, and hence global over the Internet.

Harry.

 

so, if DNS converts a 'friendly' name into an IP, how does it do this without interacting with DHCP? how does it know that pc1 is equivalent to asking for 192.168.1.12??

 

Ah - I see what you are getting at here.

Outside of the Microsoft world, on the Internet at large then the DNS servers are loaded for the local info by hand.

If a DNS query isn't for a local box it is sent to other servers until it is answered.

As a quick example: You want to contact www.tech-unity.com. Your local DNS (being in the UK in my case) doesn't know this one, but *does* know the server where .com addresses can be looked up, so asks there.

In the case of dial-up and DSL with dynamic IPs the 'name' is often dynamicaly constructed on the fly. Where this isn't the case the name is retreived from the RADIUS server.

What *exactly* happens in the Microsoft world I'm not sure, but I suspect that the DHCP server updates AD, and the DNS queries AD. Any Microsoft gurus want to comment?

Harry.

 

It is amazing what a leisurely bath and dinner will do!

I need to correct some previous points.

DHCP is not involved in 'logging on'. It just sees a request for an IP address, nothing more. It doesn't know the identity of the person requesting this. So it provides an IP address.

This includes some info about the local network, which enables Windows to 'login' to the domain. It is *this* that updates AD as to what is happening.

I base this on my work domain, in which all machines have machine generated 'domain' addresses, no matter who is actualy logging on. If you need to find out more then you need to use M$ tools.

Harry.

 

Harry, in Windows, you can chose to allow DHCP to update the local DNS entries on behalf of clients that may not support Windows dynamic DNS i.e. legacy and non Microsoft OS's.

Clients that can register themselves in local DNS directly, are Windows 2000/XP and Microsoft server boxes etc.

 

Out of the two, concentrate on DNS more, since it's literally everywhere. Active Directory can't live without it, and the Internet is based on it. I like Harry's explanation that DNS is IP based, and DHCP (in it's basic form) is ethernet-based. A DHCP server (i.e. Windows 2000/2003) can, however, offer several settings and options that enhance IP address allocation. Home routers usually have a DHCP server, but it's normally very restricted -- IP allocation only. Here's some good links:

DNS on Windows 2000

DHCP on Windows 2000

They are simple setups in Windows 2000. To truly understand DNS (at least), it's a bit of a history lesson:

DNS Wiki

DHCP Wiki

Happy reading!