DHCP routers

cdad2000

Hey everybody,

When would a router be preferred over a server to assign IP address( DHCP).

dtlokee

When there is no server to do it!

There can be many factors that play into the choice to use DHCP on a server vs using DHCP on the routers. Some of the ones that come to mind invilve remote servers with no servers to install DHCP on, it makes sense to use the router for DHCP incase the link to other sites becomes unavailable. It can also become a political issue if the servers and the network infrastructure are controlled by different groups of administrators. Typically IP addressing design falls to the network engineers so they choose to keep DHCP on the network infrastructure devices they control (routers).

Also the idea of keeping a conflict database on a Cisco rotuer is a bit chunky.

r_durant

When there is no server to do it!

Agreed!! My former company was bought over and during the network transition, the Domain Controllers/DHCP servers were not ready yet, since there was also IP addressing change as well, so the pools were setup on a router...As soon as the servers were rolled out, DHCP was disabled on the routers...

networker050184

Some of the ones that come to mind invilve remote servers with no servers to install DHCP on, it makes sense to use the router for DHCP incase the link to other sites becomes unavailable.

Main reason we use it is this ^. Remote sites pulling services from the main site where all the services are located. We migrated the main site over despite not wanting to due to the other reason dtlokee stated of having two seperate departments controlling the netwrok and the servers.

joshgibson82

Just one thing to watch out for...

If the site will use almost the entire pool of addresses, make sure to put in the global command "no ip dhcp conflict logging" ....I think that's the command...or else the router can run out of addresses due to the fact that the dhcp server pulls addresses with any conflict out of the pool for available use. I ran into this issue and was constantly having to reset the pool. I thought it was an IOS bug, but it was actually just doing its job. The command above solved my issue.

kafifi13

I wouldn't recommend doing this. just setup a server with W2k3 and set it up for DHCP

dtlokee

kafifi13 wrote:

I wouldn't recommend doing this. just setup a server with W2k3 and set it up for DHCP

I wouldn't recommend doing this either, think about the cost of hardware and software for a server, then the ongoing maintenence. At a branch office with 10 users would it make sense?

kafifi13

Really depends on your hardware and really your topology. Where your main DHCP server is located. If you have multiple sites connected together then maybe you want them all to connect to 1 DHCP server which is handing out all the IP addresses. If your talkinga bout just 1 site with 10 people then yes a router will do.

Again it depnds on alot of things. Including the company. We have 3 remotes sites. One of which only has 4 people. They are still using the Main DHCP server that is setup at the main(hub) office. If this is a big company which has it's own servers, my guess is that they are using something like Windows server 2000 or 2003 anyway. Get a box setup for DHCP and set your scope for what addresses are to be availble and your good. If you need to switch out your routers in teh future you don't have to worry about any new configurations. you will have a centralized server to do all of your DHCP. Let your routers do it's routing.

networker050184

If you need to switch out your routers in teh future you don't have to worry about any new configurations. you will have a centralized server to do all of your DHCP.

And what happens when you need to switch out your server?

It is more practical to have small remote sites pull addresses from their router. You need the router there like dtlokee stated so why not run the DHCP off of it? Its not going to consume enough recources to degrade the routing. Also if you put a server in you need people with server expertise that means even more money.....

dtlokee

In most cases the decision comes down to who controls the IP addressing. If the network engineers contril the IP addressing design then they will likely want put DHCP on the devices they can control, the rotuers and switches. If the network admins control IP addressing then it will generally be placed on servers. I think the case here is your company is small enough that you control both parts so the choice for you is to use the Windows servers to do it.

kafifi13

networker050184 wrote:

If you need to switch out your routers in teh future you don't have to worry about any new configurations. you will have a centralized server to do all of your DHCP.

And what happens when you need to switch out your server?

It is more practical to have small remote sites pull addresses from their router. You need the router there like dtlokee stated so why not run the DHCP off of it? Its not going to consume enough recources to degrade the routing. Also if you put a server in you need people with server expertise that means even more money.....

Your exactly right. Like i said it depends on your topology. If i have a large network it's easier in my judgement to have 1 dhcp server for alls sites. If you have a small ma and pa operation then yes going with DHCP on routers will work. It's not hard to maintain a DHCP server.

It's like using VPN on your firewall. It's there but if you have the money get a concentrator. Let the firewall do it's job in protecting the network and let the Concentrator worry about VPN.

To me it's the same. Let the router do the routing and the DHCP server handle the Ip address assignment. There is really no right or wrong answer.