| What is it? | TCP/IP commands. | Hardware? | Terminology used |
The core of the strength of Unix machines are flexibility vis-a-vis networking. It will not be wrong to say that networking was first tested and developed successfully on Unix machines in late 1960's and early 1970's. Today core of Internet is run on Unix machines, which range from Lynix to Sun, HP to SCO. More then 70% of the Internet Service providers use Apache Web server which run on Unix Machines. Sun systems even developed diskless Unix machines networked to other machines. There are two types of protocols available on Unix machines, UDP and TCP/IP. Most Unix machines are connected through standard RJ45 cables with TCP/IP protocol. TCP/IP protocol was developed to network unix machines and now it has become Industry standard of communications on Internet. Model of TCP/IP is slightly different from OSI (OSI has seven layers TCP/IP four layers). TCP/IP consists of
Data is passed down the stack when it is being sent to the network, and up the stack when it is being received from the network. Each layer in the stack adds control (actual bytes) when it is sending and subtracts (actual bytes) when date is received and moved up the stack. For example, consider a data packet which consists of five bytes and you want to send it to your friend over Internet. So, application layer passes your data to transport layer which adds its control in bytes to this data making it data+application+transport and passes it to Internet layer which adds its control in bytes to data+application+transport+Internet layer and passes it to network access layer which adds its control and makes it data+application+transport+Internet+network access and sends all the bytes over network. Now receiving computer's network access first reads network bytes and compares it to its records and then strips data+application+transport+Internet+network to data+application+transport+Internet and pass it to its Internet layer, which reads and do its computation and strips it to data+application+transport and so forth until data is passed on to application layer.
Here is how telnet application works. You issue telnet command which sends out its bytes down the protocal
stack and is transported to server computer. Server computer's network access layer passes it up the stack
stripping down its controls bytes and at end to kernel. Kernel issues login: and sends it back to client. Then
client enters its login name and so forth. Important files where all protocols are declared is called /etc/protocols,
lowest layers looks at data and knows that those bytes being number 6 are on TCP protocol, etc. Then ports are
defined in a file called /etc/services which is a part of application layer. If data comes with order to open
port 25 (which is smtp or simple mail transport protocol) it knows which application to open for e-mail (sendmail).
an example few entries in /etc/protocols file
ip 0 IP # internet protocol, pseudo protocol number icmp 1 ICMP # internet control message protocol igmp 2 IGMP # internet group management protocol ggp 3 GGP # gateway-gateway protocol tcp 6 TCP # transmission control protocol pup 12 PUP # PARC universal packet protocol udp 17 UDP # user datagram protocol
an example of few entries in /etc/services file
echo 7/tcp echo 7/udp netstat 15/tcp ftp 21/tcp telnet 23/tcp smtp 25/tcp mail time 37/tcp timserver time 37/udp timserver name 42/tcp nameserver whois 43/tcp nicnameback to top
To configure a host to run TCP/IP you will need the following information. Every host must have a unique IP address and hostname. If you are planning your LAN to be on Internet then you need to fill out an application with NIC (or whoever provides it) and you can buy true Internet network license for your LAN. Class C are cheapest and upto 255 hosts can be configured with IP supplied (price is still not less than $10,000). Depending on the networking consider following:
You will also need to make sure that TCP/IP is installed in kernel of your system. Although everything can be done from command line but I recommend using system administration utility for TCP/IP configuration. Using System admin utility to configure system can assure a correct configuration.
A configprogram is used to build an operational Unix kernel (for example Sco's netconfig).
RIP Routing information protocol and DNS domain name server are started by daemons at system startup. RIP uses routed and DNS uses named daemon. Check your /etc/rc.local or /sbin/rc.* files or your startup files in init.d directory for more information. Internet daemon inetd is also started from bootup and it reads configuration file /etc/inetd.conf. Example inetd.conf file
ftp stream tcp nowait root /usr/local/etc/ftpd ftpd telnet stream tcp nowait root /usr/etc/in.telnetd in.telnetd name dgram udp wait root /usr/etc/in.tnamed in.tnamed # Shell, login, exec, comsat and talk are BSD protocols. shell stream tcp nowait root /usr/etc/in.rshd in.rshd
subnet masking concept is used to overcome distance limitations (by assigning a new ip address to join cables each time over 500 metres (for ethernet), 300 meters (for thin TWP), is used to interconnect dissimilar physical networks (i.e. two different LANs, one token ring and another ethernet), is used to filter traffic between networks (local traffic stays on local subnet, only traffic for other networks is forwarded to gateway).
ifconfig command is used to configure TCP/IP on system. Here are different uses of ifconfig: ifconfig -a will display information about interface on system. output is