AIX 5L SysAdmin I: (Unit 16) – Networking Overview

Objectives:
—————–
1. Define the basic TCP/IP terminology
2. Configure TCP/IP for an Ethernet or Token-Ring connection
3. Use come of the standard TCP/IP facilities to:
-Log in to another system (telnet)
-Transfer files (ftp)
-Run commands

What Is TCP/IP?
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1. Transmission Control Protocol/Internet Protocol (Platform Independent)
2. Software to enable different systems to exchange data over a variety of types of network
3. The way in which systems are connected and how data is passed between them is transparent to the user
4. TCP/IP is vendor-independent. Development is overseen by the “Internet Architecture Board”

An Internet:
—————–
1. A TCP/IP network is often called an internet.
2. Individual machines are called hosts. Hosts may vary in size and fuctionality but have equal standing as far as TCP/IP is concerned.
3. Hosts which link two or more physical network segments to each other are called gateways

Names and Addresses:
———————————–
1. Each system in a TCP/IP network is given a name called a hostname
For example: sys3
2. When contacting another system you only need to know the name
For example telnet sys3
3. When contacting another user you need to know the system and user name
For example mail fred@sys3
4. Each system will have one or more TCP/IP addresses
For example 128.27.9.13
Note: If you know the address but not the name, you can use some TCP/IP facilities with the address

IP ver.4 – 128.27.9.13 – each number is 8 bits thus called octtect

TCP/IP Network Facilities:
————————————–
Server (RS/6000) – Disk storage, Printers, Programs, Login, Sessions
Network Management (Mail)
Network (Other Systems)
File Transfer
Clients (PCs)

Standard TCP/IP facilities include: Mail, File Transfer, Remote Login, Remote Execution, Remote Printing
A number of AIX Applications use TCP/IP:
– Network File System (NFS)
– Network Information Services (NIS)
– Domain Name Service (DNS) – Maps hostnames to IP addresses
– Dynamic Host Configuration Protocol (DHCP) – Creates temporary addresses
– Network Computing System (NCS)
– Distributed Computing Environment (DCE)
– X Windows and AIXWindows
– TME 10 Netview for AIX

Information Needed to Configure TCP/IP:
———————————————————–
1. Addresses – Each adapter is given a unique TCP/IP address and often a subnet mask. These will usually be assigned by your network administrator
2. Names – Each machine has a unique hostname and – Each machine must have access to a table of name to address translations.
This can be either:
– /etc/hosts file
– Domain Name Server – You must know:
– Domain Name
– Address of the Name Server
3. Routes – In order to communicate with systems in other networks, you may need to find the address of the default gateway.

Note: The subnet mask takes the octnet and determines where the break is between the network address and the host address.
Subnet Mask Example 255.255.255.0 (the first 3 255s identify the network and the last identifies the host)

Configuring TCP/IP:
—————————–
# smit mktcpip

HostName – sys1
Internet Address – 192.9.200.1
Network Mask – 255.255.255.0
Network Inteface – eno (ethernet)
NameServer
Default Gateway – 192.9.200.192

Note: DNS is a much easier way to manage the id addresses and hostnames instead of using the /etc/hosts file

Flat Name Resolution:
———————————
# more /etc/hosts

Internet Address Hostname #Comments
127.0.0.1 loopback localhost
192.9.200.1 sys1 timeserver
192.9.200.2 sys2

Identifying the Hostname
————————————
hostname command
# hostname
sys3

host Command
#host sys3
sys3 is 9.25.35.10, Aliases: sys3.washington.ibm.com

# host 9.25.35.10
sys3 is 9.25.35.10, Aliases: sys3.washington.ibm.com

Basic TCP/IP User Functions:
——————————————–
The following commands work with an TCP/IP system (not just UNIX/AIX)
ping – Test connectivity
ftp – File Transfer Protocol
telnet – Remote Login
rexec – Remote Execution

Lab:
——–
rmdev -dl en0 – completely remove existing ethernet network configurations so that there is no residual information existing
rmdev -dl ent0
-d – delete from the database
en0 – ethernet
hostname “” – clears out the hostname
vi /etc/hosts
cfgmgr – Run the Config Manager (sets up the network adapter)

smit – Communications
TCP/IP
Minimum Config
en0
Hostname – sys1
Internet Address – 9.19.98.1
Subnet Mask – 255.255.255.0
Use a domain server or /etc/hosts

Test configuration:
ping sys2 – not working
ping 9.19.98.2 – working
vi /etc/hosts – resolve or map the hostname and the IP address

host sys2
host sys8

netstat -i (displays the network configuration)
Name Mtu Network Address
en0 1500 link#3 0.6.29.ba.5b…
en0 1500 9.19.98 sys1
lp0 16896 link#1
lp0 16896 127 loopback
lp0 16896 ::1

Note: loopback – means that I can communicate with myself

tn sys2 – telnet to sys2
login
hostname
sys2
pwd
vi sys1file
This is my file
This is my file
ls sys1file
sys1file
exit – close connection
hostname
sys1
ftp sys2
login
ftp> get sys1file ftpdoc – transfer the file back to my system calling it ftpdoc
ftp> lcd /home/team01 – local change directory
ftp> !ls -l – execute the ls command on my local system
ftp> put localfilename
ftp> quit

FAQs:
———–
Q: Why doesn’t SMIT display properly when I telnet to my AIX machine from my PC?
A: This is usually a result of not setting the proper TERM variable. Unless you set the TERM variable correctly, AIX may not be translating the display information correctly. Try setting your TERM variable to vt100: export TERM=vt100.
?????
Q: The minimum configuration screen seems like the easiest way to set up network interface.? Why not always use that?
A: It is the easiest way to set up the network interface.? However, if you have two network interfaces on the same machine (a machine with two adapters), when you are setting up the second interface,? you do not need to reconfigure things like the host name. ?Use minimum configuration for the first interface and the further configuration for all others.

Q: Is there a reason I should use rlogin vs telnet??
A: You can set up configuration files that will enable you to ?rlogin? to a machine without the machines checking for a password.? The files that you need to configure is /etc/hosts.equiv or $HOME/.rhosts.? These files contain a list of trusted hosts that you will allow users from those machines to go directly to an existing account.? Telnet has no automated process for login.? Be careful using the .rlogin and /etc/hosts.equivfile.? You don?t want just any machine logging into you system.

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