TCP/IP Settings in XP

Before you start

Objectives: learn how to enter static TCP/IP configuration on XP machine and which tools can be used to troubleshoot connectivity.

Prerequisites: you should know what parameters should be entered for network connection. Also, you should know what is IP address and what is MAC address.

Key terms: address, ip, default, server, gateway, network, tcp, apipa, configuration, ipconfig, alternate, dns, local, protocol


Entering Information

Along with the IP address and the Subnet Mask, we can also enter information about Default Gateway and DNS server. There are two ways of entering all this information. The first way is manual entry, and we call that Static Configuration. The second way of entering this information is using Automatic Configuration. For automatic configuration we use a service called Dynamic Host Configuration Protocol (DHCP). If the client is configured to use DHCP for configuration, but is unable to contact one, it will configure itself. This means that it will use the function called the Automatic Private IP Addressing, or APIPA. The APIPA network address is 169.254.0.0, so it is easy to tell if the computer is using APIPA.

To configure basic TCP/IP settings, open the Control Panel, and open Network Connections.

 Network Connctions

Image 229.1 – Network Connections

By default, Windows XP will configure the connection to use TCP/IP. To edit TCP/IP settings, right-click the Local Area Connection and open its properties. Select the Internet Protocol (TCP/IP), and then click the Properties button.

 Internet Protocol Selected

Image 229.2 – Internet Protocol Selected

Internet Protocol Settings

Image 229.3 – Internet Protocol Properties

By default, TCP/IP is configured to receive both the IP address and the DNS server address from a DHCP server. Let’s change that to static configuration. First, we must check the ‘Use the following IP address‘ option. Then, we will enter 192.168.1.70 as our IP address. The Subnet mask will be 255.255.255.0, and the Default gateway will be 192.168.1.1. In order for the Default Gateway to be valid, it needs to be on the same subnet as the IP address. In this example notice that the IP address and the Default Gateway are both on the network 192.168.1.0. DNS server will be the same as our Default gateway.

 Static Configuration

Image 229.4 – Static Configuration

We can manually enter DNS server, while the IP address can still be assigned automatically. Also notice that we can’t get a DNS server address automatically if we are using static IP address. DNS servers don’t need to be on the same subnet as the IP address, but they do need to be accessible through the Default Gateway.

Windows XP includes a new feature that lets us configure an alternate IP address for connection. This alternate address is used when the computer cannot contact a DHCP server for its address. We can use the alternate IP address for computers that connect to networks without a DHCP server, or to configure a backup IP address in case the DHCP server goes down. To edit alternate settings for TCP/IP, click on the Alternate Configuration tab in Internet Protocol Properties.

Alternate Configuration Tab

Image 229.5 – Alternate Configuration Tab

By default, our computer is configured to use Automatic Private IP Addressing (APIPA). Let’s imagine that our computer will connect to two different networks, one with DHCP, and one without DHCP server. If the computer can’t find DHCP, it will self configure it self using an Automatic Private IP Addressing scheme (APIPA). The default network address for APIPA is 169.254.0.0. Sometimes APIPA is not desirable, because we may be using some services that require that we use static or predefined IP address. To avoid APIPA we can set Alternate Configuration for TCP/IP.

First, we have to select ‘User configured‘ option. In this case, for alternate configuration we will set 172.16.0.10 as IP address, 255.255.0.0 as Subnet Mask, 172.16.0.1 as our Default gateway. Preferred DNS server will be the same as our Default Gateway.

Alternate Configuration Configured

Image 229.6 – Alternate Configuration Configured

Now, when the computer boots and cannot contact a DHCP server, it will use the manually configured alternate address.

Address Resolution Protocol (ARP)

IP address is used to transfer data between various networks and MAC address is used by network devices to communicate on the local network. The bond between the IP address and the MAC address is made trough the Address Resolution Protocol (ARP). The function of the ARP is to take the IP address and link it to the physical address (MAC address) of our particular device. Every network interface card is assigned a hardware address. To check ARP settings, go to the CMD, and type the arp /a command.

 ARP

Image 229.7 – ARP Cache

Using that command we can see the content of our ARP cache. We can see the IP address and the Mac addresses of every computer that we’ve talked to. The cache stores this information for total of two minutes. If we reuse that information inside of the two minutes, the information is kept for ten minutes. After ten minutes, information is purged form cache.

Troubleshooting

There are several tools that we can use to troubleshoot connectivity problems in Windows XP. The first tool is ipconfig utility.

IPCONFIG

To use ipconfig, first we have to open command prompt. Then we can type in ipconfig. We can also use switches with that command, and the most common used switch with ipconfig is ‘/all‘.

 ipconfig

Image 229.8 – IPCONFIG /ALL

Using ipconfig tool we can verify our IP address, Subnet mask, Default Gateway, etc. If we use DHCP, and we have some problems, we can try and use the ‘ipconfig /renew‘ command to try and renew the IP address from the DHCP server. If this does not help, we’ll need to do additional troubleshooting to find out exactly what is wrong. If we see an IP address of 169.254.0.0 network, then we know that the DHCP was not available, and that our computer used APIPA for auto configuration.

PING

The other tool we can use is Packet Internet Groper or ‘PING’. This tool allows us to send small packets to particular machine to see if it will respond back to us. Microsoft recommends the following order for using the PING. First we should test the Loopback Address which is 127.0.0.1. By pinging this address we are checking that the TCP/IP protocol stack is properly installed. The next address to ping is the local IP address assigned to the machine. This ensures that the communication to our NIC is possible. If we have done ipconfig, and if it was successful, the ipconfig already did the same two steps that we mentioned. The next step is to check the communication with local hosts. To do that, we can ping the Default Gateway since it is also on the local network. By pinging Default Gateway we check that our local network is up and running. The next ting to do is to ping remote hosts. In this case we are checking the connectivity between the Default Gateway and the remote host. If this is was not successful, we know that we have problem with our Router.

ping

Image 229.9 – PING

TRACERT

Another tool we can use is tracert (trace route). By typing in tracert and then the destination IP address or host name, we can see the route that our computer will take in order to communicate with the destination. We will see all the Routers that we will use in order to get to destination, and also we will see the the responsiveness from all those particular Routers.

 tracert

Image 229.10 – TRACERT

PATHPING

To get more even more information we can use the ‘pathping’ tool. This tool is a combination of ‘tracert’ an ‘ping’, and it enables us to see how fast particular Routers respond back to us. We will also be able to see the entire route taken from our computer to the destination computer.

pathping

Image 229.11 – PATHPING

Using these tools we can see which Router is causing problems. In the example above, we can see that our Internet Service Provider is using firewall to prevent pathping requests being made. We know that because there are ‘*’ at the third hop (after our Default Gateway).

Remember

When configuring TCP/IP settings, we have to enter IP and Subnet Mask at minimum. For full connectivity we should also enter Default Gateway Address and DNS server address. By default, XP will configure our connection to use DHCP. If the DHCP server can’t be contacted, it will use APIPA. We can also configure alternate IP address, in which case APIPA will not be used. ARP is used to take the IP address and link it to the physical address (MAC address) of our particular device. We can use IPCONFIG /ALL command to check our TCP/IP settings. We can use PING tools to check connectivity with another host. We can use TRACERT command to check the route that our computer will take.

Commands that are mentioned in this article

Commands are entered in CMD.

arp /a – display ARP cache

ipconfig /all – verify IP configuration

ipconfig /renew – renew the IP address from the DHCP server

ping – test a network connection

tracert – check the route to the destination

pathping – trace route and provide network latency and packet loss

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