Understanding Windows XP routing table

[sailor]

I am trying to understand the Windows XP routing table and how the routing is done. For example:

  Active Routes:
  Network Destination        Netmask          Gateway       Interface  Metric
1)          0.0.0.0          0.0.0.0      192.168.1.1   192.168.1.100       30
2)        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
3)      192.168.1.0    255.255.255.0    192.168.1.100   192.168.1.100       30
4)    192.168.1.100  255.255.255.255        127.0.0.1       127.0.0.1       30
5)    192.168.1.255  255.255.255.255    192.168.1.100   192.168.1.100       30
6)        224.0.0.0        240.0.0.0    192.168.1.100   192.168.1.100       30
7)  255.255.255.255  255.255.255.255    192.168.1.100   192.168.1.100       1
  Default Gateway:       192.168.1.1

I understand the basic concepts in the headers (destination, mask, gateway, interface, metric). What I am trying to understand is how the routing algorithm is implemented based on that table.

I see the order of the table is by destination but in what order are the lines evaluated? Does the order of the lines affect the routing? Several lines (rules) might apply to one single destination. How are they chosen? I know lower metric is chosen over higher metric.

What I would like to do in the end is have two (or more) network adapters and design the routing table myself. For example, maybe, one network adapter for Internet traffic and another adapter for the LAN.

ETA: Furthermore, even though it lists the table then any attempt to edit it gives an error:

C:\Documents and Settings\A>route delete 224.0.0.0
The route specified was not found.

C:\Documents and Settings\A>route delete 224.*
The route deletion failed: The parameter is incorrect.

Why is this?

 

[jjeff1]

You're making it more complicated than it really is.

When you configure an IP address on an interface, that network is considered locally attached, and all traffic bound for that network will go out that interface.

In your case, you have 1 NIC, and it's IP is 192.168.1.100, with a subnet mask of 255.255.255.0. Anything on that network, that is 192.168.1.0 to 192.168.1.255, will go out that interface.

The next statement you have to worry about is your default gateway, which is your statement #1, destination 0.0.0.0. This tells your PC that any other networks it doesn't know about, it should send the traffic to 192.168.1.1.

So, you want to have LAN traffic off one interface and WAN off another. So you'd install a 2nd interface, then configure a NEW network on that interface. If the new interface were your WAN only interface, you'd connect it to the router, and program the default gateway into it.

The LAN interface would have to be on a different network, eg 192.168.5.0, and anything else on the LAN you wanted to access via that interface would also have a 192.168.5.0.

if it helps, draw 2 clouds, now put your PC between those clouds. Each cloud is a network, your PC can access either one, but only via the interface attached to the cloud. You want to get to another network, ie the Internet? put another device hanging off the other side of one of the clouds. To get to the internet, you go through the cloud, to that device.

 

[sailor]

Thanks, that was very clarifying and helpful. It does make things simpler for me. I will experiment and observe how the routing table changes automatically.

One more question, what happens if there are two attached networks and *both* have internet access? Can Windows handle this? Will it use one (lower metric) exclusively and if that one does not work the other one exclusively? This is what I would expect as I would not expect Windows to use both at the same time but I would expect that it could handle being connected to the internet by more than one route.

By the way, I noticed that Windows XP will not allow you to edit or delete an entry in the routing table which was automatically created by Windows but you can get around that by ADDing the exact same entry and now you own it and can edit or delete it.