Changinging configuration of a network - DHCP (IP scope)

[Koldov]

Hi All,

 

Not sure where to post this, but...

 

Asking to enhance my knowledge, so please excuse my ignorance on the subject.

 

How much work would you say it would need to remote in and change the I.P. scope given out by the DHCP server on the core-switch from one range to another?

 

We have VLANS half of which aren't used, which I'm not really sure we need (not that I have the required knowledge to make an informed choice), but obviously seemed to be a fashionable practise when it was installed - also just from a bit of research a flat network seems to be preferable (that would save me a few headaches getting certain apple devices to talk to printers and air-server and the mac-mini used as an update cache and... anything Apple related it seems).

 

However, I digress... Can anyone can give me a basic overview of what is required?

 

Thanks in advance.

 

Kol.

[Steve21]

As in to get all the clients on a single VLAN?

 

Only thing that would really need changing is the VLAN tag on the switches. Doesn't matter if there's 100 VLANs configured if you stick them all on a single vLAN lets call it 10, all will be "flat"

 

In regards to DHCP/server wise that depends on things like how many devices and whether you'd need to expand scopes etc.

 

Generally it's not advised to use a flat one though, as security/management wise it's a lot worse

 

Steve

[Koldov]

 

In regards to DHCP/server wise that depends on things like how many devices and whether you'd need to expand scopes etc.

 

 

Steve

 

Haha! No, the 'FLAT' network was just a gripe on my part

 

Literally this, just changing the scope on the DHCP to give out a different set of addresses...

 

We only use four of our VLANS, they don't have a huge amount of clients each and we have been given a /21 address range - so plenty of room to carve that up?

 

I'm just wondering how much work it would take to log onto the DHCP in the switch and tell it to give IP addresses from this range in those 4 vlans instead of the current ones?

 

Kol.

[Julian]

You have not mentioned what brand of central network switch you are using. This will also need programing so that it can get the data from your revised vlans to where it is needed. If you are merely tweaking your existing vlan, that is simple, completely different ip ranges (ie 172.16.*.* to 192.168.*.*) is more work.

[twin--turbo]

So DHCP is commin from the switch, not a server.

 

Do you have a management network for the switchws?

 

What brand of switches..

 

Time? if it's all relativly correct so far, 2-3 mins of work on most common switch OS's

 

TT

[Koldov]

completely different ip ranges (ie 172.16.*.* to 192.168.*.*) is more work.

 

So DHCP is commin from the switch, not a server.

 

Do you have a management network for the switchws?

 

What brand of switches..

 

Time? if it's all relativly correct so far, 2-3 mins of work on most common switch OS's

 

TT

 

Yes, a completely different set of ip ranges (and I'm looking to get the VLANS cleaned up and half of them deleted), CISCO switches, yes I think there is a management network, DHCP is done from the network not a server.

 

Kol.

[twin--turbo]

Should just be a couple of one liners on IOS, long time since I have looked at DHCP on one though. But can't see it being more than a few mins work.

[Julian]

DHCP requests, come from the server, but go through the central switch. When the server is on one vlan, and the requesting computer is a different vlan, then switch has to be programed how to handle the request.

 

In addition for the switch to route between vlans (layer3) the switch has to have its own ip address on each vlan (this address will be the gateway address for that vlan).

 

Because of both of the above points, when changing the range of ip address DHCP gives out for a vlan, it may be necessary to change the settings that your network switch uses for routing your data.

[twin--turbo]

DHCP requests, come from the server, but go through the central switch. When the server is on one vlan, and the requesting computer is a different vlan, then switch has to be programed how to handle the request.

 

Not from what the OP says. They are using the Cisco as the DHCP server.

 

As soon as a VLAN is given an IP then that enters the routing table as a CONNECTED route which is classed as the most reliable route.

 

If the helpers are configured to point a the local switch DHCP server, and there is a range in the local switch relating to the VLANS Subnet then the local switch will serve the DHCP.

 

TT