Configuring IP and DNS

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Configuring IP

First, a little terminology. The campus has two Class B network address spaces, 128.194.0.0 and 165.91.0.0. These spaces are "variably subnetted". This means that a particular network within these two spaces is specified by a network number and a network mask. The network mask will vary from network to network within an address space. The network mask determines which part of an IP address describes the host number and which part describes the network number.

For example, the network mask of 255.255.255.128 along with a network number of 165.91.45.128 results in a network with 126 host addresses. The host addresses are 165.91.45.129 thru 165.91.45.254. A concise way of specifying this network is 165.91.45.128/25 where the /25 specifies that the top 25 bits of the network mask are set to 1.

Here is a table of sizes:

Network Size	Network Mask	Bits set to 1
2	255.255.255.252	30
6	255.255.255.248	29
14	255.255.255.240	28
30	255.255.255.224	27
62	255.255.255.192	26
126	255.255.255.128	25
254	255.255.255.0	24
510	255.255.254.0	23
1022	255.255.252.0	22
2046	255.255.248.0	21

Typically, each building on campus will have one or two networks within it. In the past, the last host number on the network (typically 254) was used as the default router for the network. This policy is being changed due to the introduction of variable length networks. It will now be host 1. For instance in the example above the default router would be 165.91.45.129.

For instance, assume your IP address is 128.194.1.42 on network 128.194.1.0/24. Applying the network mask of 255.255.255.0 (24 one bits) to that address gives you a network number of 128.194.1.0 and a host number of 42.

Typically, configuring IP on a machine consists of the following three steps.

1. Configure your IP address
2. Configure your network mask
3. Configure your default router/gateway

All of this information is provided to you via NIM.

Contact Help Desk Central at helpdesk@tamu.edu or 845-8300 if you need more assistance configuring IP on your machine. They will attempt to assist you or will point you to a more appropriate source of information.

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Configuring DNS

Configuring DNS varies widely from platform to platform. The following are instructions for the more common applications and operating systems.

1. Windows 95

   Modem Users with TAMUNet installed:

   1. Double-click My Computer
   2. Double-click Dial-Up Networking
   3. Single-click TAMUNet Connection
   4. From the menu bar, select File and select the Properties
   5. Click Server Type...
   6. Click TCP/IP Settings...
   7. Click Specify name server addresses

   Ethernet Users:

   1. Double-click My Computer
   2. Double-click Control Panel
   3. Double-click Network
   4. Click TCP/IP
   5. Click Properties
   6. Click the DNS Configuration tab
   7. Click Enable DNS

2. UNIX

   Nameservice is configured via the /etc/resolv.conf file on most UNIX systems. The file contains a line specifying the domain, followed by multiple nameserver lines (you should use the order recommended for your location):

   domain tamu.edu
   nameserver 128.194.254.1
   nameserver 128.194.254.2
   nameserver 128.194.254.3

   Note that enabling DNS is usually configured elsewhere. Methods of enabling DNS vary from UNIX system to UNIX system.

3. Macintosh (MacTCP)
   • Bring up the 'Control Panel' Folder
   • Double click 'MacTCP'
   • Click on `More...'

   Domain information is located in the lower right corner.

   Use 'tamu.edu.' for the Domain on all entries (note the trailing '.'). Fill in the list of IP Addresses and include one entry with a domain of '.' by itself. Use the IP address of the first name server in the recommended list for this domain. Set the "default" name server to be the `tamu.edu' name server that is first in the recommended list.