Slackware Linux Essentials
Prev	Chapter 5 Network Configuration	Next

5.3 TCP/IP Configuration

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At this point, your network card should be physically installed in your computer, and -the relevant kernel modules should be loaded. You will not yet be able to communicate -over your network card, but information about the network device can be obtained with ifconfig -a.

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-# ifconfig -a
-eth0 Link encap:Ethernet HWaddr 00:A0:CC:3C:60:A4
-UP BROADCAST NOTRAILERS RUNNING MULTICAST MTU:1500 Metric:1
-RX packets:110081 errors:1 dropped:0 overruns:0 frame:0
-TX packets:84931 errors:0 dropped:0 overruns:0 carrier:0
-collisions:0 txqueuelen:100
-RX bytes:114824506 (109.5 Mb) TX bytes:9337924 (8.9 Mb)
-Interrupt:5 Base address:0x8400
-
-lo Link encap:Local Loopback
-inet addr:127.0.0.1 Mask:255.0.0.0
-UP LOOPBACK RUNNING MTU:16436 Metric:1
-RX packets:2234 errors:0 dropped:0 overruns:0 frame:0
-TX packets:2234 errors:0 dropped:0 overruns:0 carrier:0
-collisions:0 txqueuelen:0
-RX bytes:168758 (164.8 Kb) TX bytes:168758 (164.8 Kb)
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If you just typed /sbin/ifconfig without the -a suffix, you would not see the eth0 -interface, as your network card does not yet have a valid IP address or route.

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While there are many different ways to setup and subnet a network, all of them can be -broken down into two types: Static and Dynamic. Static networks are setup such that each -node (geek lingo for thing with an IP address) always has the same IP address. Dynamic -networks are setup in such a way that the IP addresses for the nodes are controlled by a -single server called the DHCP server.

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5.3.1 DHCP

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DHCP (or Dynamic Host Configuration Protocol), is a means by which an IP address may -be assigned to a computer on boot. When the DHCP client boots, it puts out a request on the Local Area Network -for a DHCP server to assign it an -IP address. The DHCP server has a pool (or scope) of IP addresses available. The server will respond to -this request with an IP address from the pool, along with a lease time. Once the lease time for a given IP address lease -has expired, the client must contact the server again and repeat the negotiation.

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The client will then accept the IP address from the server and will configure the -requested interface with the IP address. There is one more handy trick that DHCP clients -use for negotiating the IP address that they will be assigned, however. The client will -remember it's last assigned IP address, and will request that the server re-assign that -IP address to the client again upon next negotiation. If possible, the server will do so, -but if not, a new address is assigned. So, the negotiation resembles the following:

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    Client: Is there a DHCP server available on the LAN?
- -    Server: Yes, there is. Here I am.
- -    Client: I need an IP address.
-    Server: You may take 192.168.10.10 for 19200 seconds.
- -    Client: Thank you.

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    Client: Is there a DHCP server available on the LAN?
- -    Server:Yes, there is. Here I am.
- -    Client:I need an IP address. The last time we
- -    talked, I had 192.168.10.10;
-    May I have it again?
-    Server:Yes, you may (or No, you may not: take 192.168.10.12 instead).
- -    Client: Thank you.

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The DHCP client in Linux is /sbin/dhcpcd. If you load /etc/rc.d/rc.inet1 in your favorite text editor, you will notice -that /sbin/dhcpcd is called about midway through the script. -This will force the conversation shown above. dhcpcd will also -track the amount of time left on the lease for the current IP address, and will -automatically contact the DHCP server with a request to renew the lease when necessary. -DHCP can also control related information, such as what ntp server to use, what route to -take, etc.

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Setting up DHCP on Slackware is simple. Just run netconfig -and select DHCP when offered. If you have more than one NIC and do not wish eth0 to be configured by DHCP, just edit the /etc/rc.d/rc.inet1.conf file and change the related variable for -your NIC to “YES”.

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5.3.2 Static IP

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Static IP addresses are fixed addresses that only change if manually told to. These -are used in any case where an administrator doesn't want the IP information to change, -such for internal servers on a LAN, any server connected to the Internet, and networked -routers. With static IP addressing, you assign an address and leave it at that. Other -machines know that you are always at that certain IP address and can contact you at that -address always.

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5.3.3 `/etc/rc.d/rc.inet1.conf`

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If you plan on assigning an IP address to your new Slackware box, you may do so either -through the netconfig script, or you may edit /etc/rc.d/rc.inet1.conf. In /etc/rc.d/rc.inet1.conf , you will notice:

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-    # Primary network interface card (eth0)
-    IPADDR[0]=""
-    NETMASK[0]=""
-    USE_DHCP[0]=""
-    DHCP_HOSTNAME[0]=""
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Then further at the bottom:

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-    GATEWAY=""
-

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In this case, our task is merely to place the correct information between the -double-quotes. These variables are called by /etc/rc.d/rc.inet1 -at boot time to setup the nics. For each NIC, just enter the correct IP information, or -put “YES” for USE_DHCP. -Slackware will startup the interfaces with the information placed here in the order they -are found.

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The DEFAULT_GW variable sets up the default route for -Slackware. All communications between your computer and other computers on the Internet -must pass through that gateway if no other route is specified for them. If you are using -DHCP, you will usually not need to enter anything here, as the DHCP server will specify -what gateway to use.

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5.3.4 `/etc/resolv.conf`

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Ok, so you've got an IP address, you've got a default gateway, you may even have ten -million dollars (give us some), but what good is that if you can't resolve names to IP -addresses? No one wants to type in 72.9.234.112 into their web -browser to reach www.slackbook.org. After all, who other than the -authors would memorize that IP address? We need to setup DNS, but how? That's where /etc/resolv.conf comes into play.

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Chances are you already have the proper options in /etc/resolv.conf. If you setup your network connection using DHCP, -the DHCP server should handle updating this file for you. (Technically the DHCP server -just tells dhcpcd what to put here, and it obeys.) If you need -to manually update your DNS server list though, you'll need to hand edit /etc/resolv.conf. Below is an example:

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-# cat /etc/resolv.conf
-nameserver 192.168.1.254
-search lizella.net
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The first line is simple. The nameserver directive tells us what DNS servers to query. -By necessity these are always IP addresses. You may have as many listed there as you -like. Slackware will happily check one after the other until one returns a match.

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The second line is a little more interesting. The search directive gives us a list of -domain names to assume whenever a DNS request is made. This allows you to contact a -machine by only the first part of its FQDN (Fully Qualified Domain Name). For example, if -“slackware.com” were in your search path, you could reach http://store.slackware.com by just pointing your web browser at http://store.

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-# ping -c 1 store
-PING store.slackware.com (69.50.233.153): 56 data bytes
-64 bytes from 69.50.233.153 : icmp_seq=0 ttl=64 time=0.251 ms
-1 packets transmitted, 1 packets received, 0% packet loss
-round-trip min/avg/max = 0.251/0.251/0.251 ms
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5.3.5 `/etc/hosts`

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Now that we've got DNS working fine, what if we want to bypass our DNS server, or add -a DNS entry for a machine that isn't in DNS? Slackware includes the oft-loved /etc/hosts file which contains a local list of DNS names and IP -addresses they should match to.

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-# cat /etc/hosts
-127.0.0.1           localhost  locahost.localdomain
-192.168.1.101       redtail
-172.14.66.32        foobar.slackware.com
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Here you can see that localhost has an IP address of 127.0.0.1 -(always reserved for localhost), redtail can be reached at 192.168.1.101, and foobar.slackware.com is -172.14.66.32.

Prev	Home	Next
Network Hardware Configuration	Up	PPP

5.3 TCP/IP Configuration

5.3.1 DHCP

5.3.2 Static IP

5.3.3 /etc/rc.d/rc.inet1.conf

5.3.4 /etc/resolv.conf

5.3.5 /etc/hosts

5.3.3 `/etc/rc.d/rc.inet1.conf`

5.3.4 `/etc/resolv.conf`

5.3.5 `/etc/hosts`