Basic networking and DHCP theory

Question

Background

We're organizing an event where we need to connect about 10 PCs into a single LAN network (no internet access). We've got some general experience with "home" and "web" networking but we've never set up a custom network for ourselves before.

Our plan

1. Get a basic managed or unmanaged switch
2. Connect all PCs to it via ethernet
3. Assign fixed IP to each one of them for easier access
4. That's it

Questions

1. Could someone with a bit more experience confirm if the above approach will "just work" as we imagine, or is there something we haven't taken into account?
2. DHCP. If we set up a DHCP server on one of the PCs, will it "just work"? I.e. if we connect a laptop to the switch during the event, will it be assigned an IP from that PC, or does the DHCP server need to run directly on the switch?

Answer 1

At the basic IP level, yes

• Static addressing will work
• Setting up one DHCP server will work
  • Either one of the PCs
  • On a small router

Most small-business switches without any configuration behave like a simple unmanaged switch, and certainly you don't need anything beyond that for what you desccribe.

By "work" I mean these:

• ping another host by IP address
• web from one host to another by IP address (on presumption you have a web server)
• SSH from one host to another by IP address (on presumption they are set up to accept SSH)

What won't work is any name-to-address translation

For short-duration small networks

• Just using IP addresses is fine
• Use /etc/hosts (unix) or hosts.txt (Windows) for the few names you need
• Set up a DNS server (not recommended if you are new to this)
• Set up Windows NetBIOS-type name resolution (not recommended if you're new to that)

Another thing which won't work (as you've described your network) is any kind of check-license-over-internet, which a lot of software uses these days.

Something which might surprise you is the amount of software which checks the reverse lookups of incoming IP addresses. For example, many telnet, SSH, web, mail server programs will reverse lookup the IP address (ie, make a DNS lookup to find the name from the IP address). These programs will normally make DNS lookup to their configured DNS server, which is possibly on the far side of a local router. These things can sometimes fail and retry rather slowly. Some applications and operating systems will let you use /etc/hosts as mentioned above.

This issue is definitely worth checking with your planned applications.

Answer 2

Welcome to Network Engineering!

Your plan is fine, as long as you assign IP addresses in the same subnet. You can, for example, use addresses 192.168.0.1, 192.168.0.2, etc. The subnet mask should be 255.255.255.0.

As an alternative, you can let the PCs assign their own addresses. All the PCs will assign themselves addresses in the 169.254.0.0 network, with the subnet 255.255.0.0. You don't have to do anything for this to happen. This method has a slight disadvantage in that you have to look at each PC to see their address.

For a small network like this, DHCP is an unnecessary complication.

Answer 3

Honestly, small business level routers are so cheap nowadays, I'd just pick up one of those for fifty bucks, pick up an unmanaged switch, and do the DHCP that way. It's a LOT easier. This way, if your situation changes, and you do need internet access, you can plug in the upstream. If your situation does not change, you can leave it alone. You can leave the router's defaults in place and have your clients use DHCP.