Arch Linux

phrakture

Arch Overlord

From: behind you

Registered: 2003-10-29

Posts: 7,879

Website

stupid static ip question

IANANG (I Am Not A Network Guru):
Can you specify a static IP on a dhcp based network?  I am assuming the ip has to be out of the dhcp range if this is possible.. like if my dhcp ips are from X.X.X.2 to X.X.X.100 can i specify X.X.X.150 as a static IP?
I want to setup a few local network boxes to handle some stuff but don't want DHCP to screw up my settings and don't want to specify static IPs for everything

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incinerator

Member

From: Edinburgh, Scotland

Registered: 2005-02-15

Posts: 80

Re: stupid static ip question

Hmmm, I should have read your posting a wee bit more thoroughly, that's why the edit.

Short answer: Yes.
Short explanation: As long as the static address you use is still inside the your local networks mask it should be safe to do so. There may still be some nasty sideeffects like routers not routing that machine but that is unlikely and you will find out early enough anyway.

Long explanation:
Any box on any IP-based network can be set to any IP address you like. It is a matter of living with the consequences of that.

If you tell a computer not to get its IP via dhcp, what happens? It will happily use its static IP (if set up) and the dhcp server won't even know about it. The danger here will be that the dhcp server "accidentally" may assign that IP to another computer just because he feels in the mood of doing so. You end up having two computers having the same IP which basically puts your network in an undefined state.

Ways to get around this are:
1.) Every network card has a unique MAC address. You can configure the dhcp-server to map the IP-address (and hostname etc.) to a specific MAC address. That way no other computer will get the IP address from dhcp (but it may still statically spoof it), which allows you to configure all computers as dhcp clientss and still being able to rely on a certain computer always having the same IP address and/or hostname. Remember, it is also very easy to spoof MAC-addresses, thus you probaly don't want to do MAC-address mapping in a potentially hostile environment.

2.) A dhcp server can be configured to only use a part of the network's available address range. All other IP addresses will be free to play with as the dhcp server won't assign them to computers.
Therefore the address range not used by the dhcp server is free to play with.

I just can't be arsed to give you exact config-file-level instructions right now. Go and find out yourself. It is not my fault that Arch Linux packages include so few manpages.

Cheers,
Dominik

phrakture

Arch Overlord

From: behind you

Registered: 2003-10-29

Posts: 7,879

Website

Re: stupid static ip question

that's what I was looking for...

and I doubt network topology lessons are contained in any of the manpages 8)

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http://phraktured.net