What is Windows XP's automatic metric feature?

A. XP introduced the TCP/IP automatic metric feature. The OS uses metrics to assign costs to IP routes that let the IP component select the "cheapest" cost route when sending packets. Traditionally, you could manually assign a cost to a route--XP lets you automatically assign a route cost according to the link's connection speed, as shown below:

Link Speed	Metric
Greater than 200Mbps	10
Greater than 20Mbps, and less than or equal to 200Mbps	20
Greater than 4Mbps, and less than or equal to 20Mbps	30
Greater than 500Kbps, and less than or equal to 4Mbps	40
Less than or equal to 500Kbps	50

Assigning route costs is useful when you have multiple network connections to one destination. In such a scenario, XP will use the fastest link connection because it will have the lowest cost.

To see the end result, from the command prompt type

route print

The following sample shows metric values assigned for multiple IP routes:

Active Routes:
Network Destination        Netmask          Gateway       Interface  Metric
          0.0.0.0          0.0.0.0      192.168.1.1   192.168.1.102       30
          0.0.0.0          0.0.0.0      192.168.1.1   192.168.1.101       20
        127.0.0.0        255.0.0.0        127.0.0.1       127.0.0.1       1
      192.168.1.0    255.255.255.0    192.168.1.101   192.168.1.101       20
      192.168.1.0    255.255.255.0    192.168.1.102   192.168.1.102       30
    192.168.1.101  255.255.255.255        127.0.0.1       127.0.0.1       20
    192.168.1.102  255.255.255.255        127.0.0.1       127.0.0.1       30
    192.168.1.255  255.255.255.255    192.168.1.101   192.168.1.101       20
    192.168.1.255  255.255.255.255    192.168.1.102   192.168.1.102       30
        224.0.0.0        240.0.0.0    192.168.1.101   192.168.1.101       20
        224.0.0.0        240.0.0.0    192.168.1.102   192.168.1.102       30
  255.255.255.255  255.255.255.255    192.168.1.101   192.168.1.101       1
  255.255.255.255  255.255.255.255    192.168.1.101               4       1
  255.255.255.255  255.255.255.255    192.168.1.102   192.168.1.102       1
Default Gateway:       192.168.1.1

In this sample, you can see two interfaces: 192.168.1.101 and 192.168.1.102. The first interface has a metric value of 20 and the second interface has a metric value of 30. The first interface, 192.168.1.101, is a 100Mbps LAN link and the second interface, 192.168.1.102, is an 11Mbps wireless network that connects to my 1Mbps broadband link. Where both interfaces are available, XP would use the lowest metric (i.e., 20), which corresponds to the 100Mbps link.

Comments

Plain text