8.3 Looking ahead

Throughout these eight sessions we been looking at networking, IP addressing and related ideas in the context of home networks. Actually, what we’ve been showing you wouldn’t just be found in homes. It would also be found in small businesses, such as shops, cafés and restaurants, solicitors’ offices, estate agents, and so on.

In large businesses and organisations, the same basic principles of IP addressing, subnet masks, DHCP, network address translation, and so on, apply. But the way they are implemented, for example the equipment used and the network structures, are more complicated. In fact, organisations like these to employ full-time network managers to keep things working.

Networks at this level areis often described as ‘enterprise’ networks, and the equipment used is described as enterprise routers, enterprise switches, and so on. Setting up enterprise equipment and networks is more involved than it is for home equipment and networks.

The next eight sessions relate mainly to the enterprise context. In this part I want to give a quick overview of the way enterprise networking differs from home networking.

As we’ve already mentioned, the home gateway, which is often informally called a router, combines the functions of a router, a switch, a DHCP server, and a Wi-Fi access point.

In the enterprise context, these are usually separate pieces of equipment, and often far from each other.

In a home gateway, the router has just two interfaces. Setting up these interfaces was mainly a matter of entering appropriate numbers in a graphical interface.

An enterprise router might have two or more interfaces. Giving an interface an IP number on one of these routers is usually done through a command-line interface, and involves several steps. It’s very different from the way you do it on a home gateway. Just to give you a flavour of what’s involved, I’ll set up an IP address on one of the router interfaces here, using the command-line interface.

I go to the command prompt of the router. I type enable. The prompt changes to a hash sign.

The next stage isn’t actually necessary, but it’s useful: show ip interface brief. It shows that there are two Ethernet interfaces, without IP addresses, and both are ‘down’, that is, not working.

So now I type a new instruction, configure terminal, and the prompt changes again.

Now I choose which interface to set up. This is the gigabit Ethernet 0 slash 0 interface.

The prompt changes again, and I key in the IP address and the subnet mask.

And then this curious instruction, no shutdown, to switch it on, or ‘up’.

Now it’s useful to go back to the show ip interface briefcommand, just to check everything looks right. And there we see that the 0 slash 0 interface has the right IP address and is ‘up’, that is working. So all that’s just for one interface.

Another distinctive feature of enterprise networks is the extensive use of subnetworking to create manageable groups of users.

For example, in a large organisation, you could have subnetworks for these groups of staff, and within each of these groups there might be further subnetworks. Typically there might be differing security policies for these subnetworks. For example, some subnetworks might only be accessible to certain categories of staff.

There might be further subnetworks for functions like printing, and subnetworks for servers providing public-facing services such as web pages, online purchasing, enrolment, and so on.

Enterprise networks also often span multiple sites, often widely separated, but interlinked so that, for the staff, there’s no difference between communicating with someone on the same site, or someone on a different site, possibly in another country.

So the world of enterprise networking is quite a step up from what we’ve been looking at so far.