Eric's Beijing Diary

A bit of a hectic week. This is a brand new institution, so it is not surprising that there should be some bugs to work out. But in this case it is particularly frustrating, because network administration has been outsourced to China Mobile, so configuration of the internal network must be done by them.

What they have done, is to set up every system in the lab so that the computers can all access the internet. That is not good enough for me. I want them also to be able to see each other, and also the instructor machine. They say this can be done if we use static IP's. In one sense, I should not object to this, because they do that in Beijing, too. But in Beijing, they have someone assigned to manage the IP addresses. I don't like it there, either, but at least someone is in charge. Here, the guy gets up in front of the class and tries to assign individual IP's to each student based on where they are sitting in the classroom, and then expects them to configure their own system. Mayhem.

Here is the issue: Each computer on a network must have an individual IP address. If you are connected to any network (such as the Internet), you can go to the Command Prompt, type IPCONFIG, and see your IP address. This address can be assigned to your computer in one of two ways. It can be assigned manually, or it can be assigned by a DHCP (Dynamic Host Configuration Protocol) server. I strongly prefer the latter method, because it doesn't require any expertise on the part of the end user. If the user can be shown how to configure his or her system as a DHCP client, which just means configuring the system to get an IP address dynamically, all other configuration, such as subnet mask, and DNS server, can be done from the server side. In addition, the DHCP server takes care of making sure that no two systems are using the same IP address.

They don't want to use DHCP here. It seems crazy, but without seeing the network schematic, I am pretty sure that they prefer static IP addresses because it allows them to create two or more virtual subnets on the same physical network. If you have a DHCP server on your network, any client on the same physical subnet could conceivably grab an IP from that server. Any two machines that get an IP address from the same server, will be on the same subnet. There is no way to keep the machines apart unless you physically subnet the network. But with static IP addresses, you can actually create two or more subnets on the same physical network by changing the subnet mask. Computers with the same subnet mask will be able to see each other (as long as that part of the IP address covered by the mask is identical), but they will not be able to see computers with a different subnet mask, even though those computers are on the same physical subnet.

Sorry for being so technical. Actually, I don't teach network engineering anymore. I have more or less specialized in database. But it sure helps to have a little of that background, given the problems I run into here, such as an institution of higher learning with it's entire internal network configuration outsourced to an offsite ISP. Anyway, I am crossing my fingers and hoping they finally get the bugs worked out by next week. I really need a working lab for the courses I teach. Stay tuned.