when to use DHCP?

yoda · 28 Sep 2006 at 14:24

the IT admin of a small company network is using DHCP for clients and servers throught the site....
as far as I'm concerned this is wrong as their is only 200 PC's at the most and their all STATIC...
It's only a single site with very few laptops...

I'm after a recognised guide, preferably cisco or microsoft that states when to use DHCP and when not....
Aparently he was told at college to allways use DHCP... - Thats his current argument againsed me.... he left college about 8 years ago...

Can someone please help me....

Thanks

shine · 28 Sep 2006 at 14:27

I've got no link to official guides but the rule is all servers should have static ip's and clients can be a mix depending on the requirements.

rpstewart · 28 Sep 2006 at 14:35

As above for servers definitely.

DHCP is just far easier to administer and deal with, no need to ensure that each PC has the right address, subnet, gateway etc, you don't need to keep track of which addresses are allocated and which aren't...

To be honest I can't think of a sensible argument for having a static IP on a machine with no server type services on it.

growse · 28 Sep 2006 at 14:36

If you have a situation where clients need a static ip (because they're routers, servers, etc), then they need static ips. If it's just clients connecting to the network, DHCP is far easier to manage.

From memory, I think DHCP tends to give out the same ip address to a mac address it's seen before, but only if it's available. If you have fewer clients than ip addresses, then the clients will nearly always get the same ip. However, this obviously doesn't guarantee that a client will get the same ip, and shouldn't be used for clients that need a static ip.

yoda · 28 Sep 2006 at 16:34

All the clients are allways connected to the network.... that have static assignments in the DHCP server...

I allways thaught that DNS and master browser functions work better with static IP addressing and it produces less network traffic.

Avalon · 28 Sep 2006 at 16:58

200 PC's with static IP's would be a major headache, if they are all built with DHCP enabled it saves a lot of agro and potential conflicts. If you have a LAN and you want to run a service of some form on it then yes without doubt static IP's.

richard smith · 29 Sep 2006 at 08:39

There is nothing wrong with DHCP. It's easier to setup, maintain and if you need to change things like DNS server/default gateways etc, a damn sight easier with DHCP. Dhcp will re-assign the same IP to machines when leases are renewed in general. You can always set an incredibly long lease time and you have essentially a static IP although there isn't really much point.

Obviously, servers, print servers, printers and routers should have static addresses.

I usually set networks up (assuming a 192.168.x.x/24) 1-30 static. Setup the DHCP scope for 31-253. 254 is our router to the rest of our group.

stoofa · 29 Sep 2006 at 09:58

Ever since I started supporting networks in general I've always used DHCP where possible.
"Only 200 machines....." DHCP - no question.
Sure some machines need static addresses, however as long as you've correctly configured DNS and it is working then the list of items that need static addresses should be very short.

If something desperately needs a static address setup a reservation via MAC address in the DHCP server.

When to use DHCP?
For me - 5 machines and above sounds good to me.

Uhtred · 29 Sep 2006 at 11:16

Why wouldn't you want to use dhcp? what if you changed your gateway and had to change all 200 pcs? As said, set your servers to static and then have a pool of addresses reserved for clients using dhcp

daztrouk · 29 Sep 2006 at 11:53

at my previous place there were about 70 odd machines, all with static. Network admin said it was easier in general to deal with....remote connections, pinging and the like :confused:

stoofa · 29 Sep 2006 at 11:59

daztrouk said:
at my previous place there were about 70 odd machines, all with static. Network admin said it was easier in general to deal with....remote connections, pinging and the like

These are the network admins who sit in the corner of their IT rooms.
When Mr. Jones walks in from accounts they look at them and say:

"Ah, 10.171.24.50 - how are you?"

Us newer generation of IT managers and Network Admins know Mr. Jones by his first name and connect remotely or ping via a computer name rather than memorising everyones IP address

Uhtred · 29 Sep 2006 at 12:09

there's something to be said for that, however it's probably easier to use comptuer names

daztrouk · 29 Sep 2006 at 12:35

stoofa said:
These are the network admins who sit in the corner of their IT rooms.
When Mr. Jones walks in from accounts they look at them and say:

"Ah, 10.171.24.50 - how are you?"

Us newer generation of IT managers and Network Admins know Mr. Jones by his first name and connect remotely or ping via a computer name rather than memorising everyones IP address

*cough*database*cough*

yoda · 29 Sep 2006 at 13:13

but, why would you ever need to change gateways or DNS servers if you set it up right in the first place????

With the exception of large companies with multiple sites....
NET: 192.168.1.X

1: Unix / Linux main server
2: Exchange
3: Proxy
4: Gateway/firewall
5-10: DNS1-5 / ADS1-5
11-30: other servers
31-50: print servers
51-251: Client PC's
Use an excel spread sheet with IP number and what it's assigned to = no conflicts...
It works, I've implemented it and in three years I never needed to change it...

shine · 29 Sep 2006 at 13:24

To keep the spreadsheet up to date is extra work that you don't need to do.

yoda · 29 Sep 2006 at 13:27

meh, for how often it changed, one change per week... at the most....

stoofa · 29 Sep 2006 at 13:27

But DHCP won't allow conflicts either - you can even check the "Ping before assigning address" option.
If the DHCP server gets a reply from an IP address that it is trying to assign (not renew) it won't allow it to be used.

Why would gateways & DNS change?
I don't know about you but our network is constantly evolving.
We will bring up new machines along side old ones before migrating and if we've setup a new DNS server it's nice and easy to bring it up, make sure it's working, change the DHCP settings, take the old server down than it would be to go and change settings manually.

Recently we replaced our Cisco router with a Dell server running IPTables.
That was very much a "run alongside" situation where the final setting change was made to the DHCP config for a painless move over.

When it comes to networks I always ask myself "Which is the simplest way of getting exactly what I need".
I look at static over DHCP and I simply cannot see anything at all that gives me any kind of benefit - what advantages does static addressing give to a network admin over DHCP?

shine · 29 Sep 2006 at 13:30

stoofa said:
I look at static over DHCP and I simply cannot see anything at all that gives me any kind of benefit - what advantages does static addressing give to a network admin over DHCP?

Job security?

stoofa · 29 Sep 2006 at 15:19

shine said:
Job security?

ROFL
Good call!!

tolien · 29 Sep 2006 at 15:20

You could even have the best of both worlds - static addressing using DHCP. That way the machines that should get the same IP all the time do, and you can remotely change their default gateway et al.