In a network that's being designed to provide wireless and wired access in a library, where there will be more or less 50 users at the same time...
Where would be better to handle the DHCP requests? Would it be better to handle all those requests at a unique point, or should I handle requests from the wired and from the wireless connections in separate ways ?
Edit: don't have the equipments yet, only a budget limit (will be $1,500 for network, including cables)
We handle them on the same server. If the server is not in the same VLAN/Network as the clients, you can use dhcp relay on the layer3 device (normally the gateway) of said network.
For example, if you have wireless going to vlan 10, wired vlan 15, and your server is on vlan 20; you'll configure the dhcp relay agent on vlans 10 and 15 interfaces to point to the server's IP address on vlan 20.
In cisco terms, the dhcp relay agent is enabled by the ip helper-address $serverIP address.
NOTE: ip helper-address is more than a dhcp relay agent. It can be used for other protocols as well. Info here: http://www.ciscopress.com/articles/article.asp?p=330807&seqNum=9
In general the use of multiple production DHCP servers within an organization tends to be a function of scale and availability.
Scale is going to be driven by the number of clients, the churn of said clients and, of course, the duration between reservation requests.
Availability is just a question of how much impact the loss of a server would create vs the cost to maintain (and synchronize) a redundant pair.
It's hard to make a definitive recommendation without knowing a bit more about the environment but at ~50 concurrent users it's incredibly unlikely that you'd be taxing just about any platform in common use today.
As to availability - losing DHCP can render the network virtually unusable. My usual tendency is to run redundant pairs if at all possible, but without knowing design/platform/budget constraints I can't really say if it would make sense in your environment.
A pair of DHCP servers could easily handle many different subnets and provides redundancy.
Separate VLANs for wired and wireless in this small network requires a little more setup, but I'd say it is still the way to go to give flexibility in security policies that might be different between the two connections types.
The advantages to sharing DHCP servers for wired and wireless are easier administration and troubleshooting, and you'll be able to create server-level options that can be shared across all scope options. For example, if you push the same DNS servers (Option 6) and DNS Domain Name (option 15) down to all of your DHCP clients, you can create these as server options, and only the default gateway/router (Option 3) needs to be different for each scope.
Please see all the answers on Setting up DHCP server on the router or on the switch for more DHCP info.
