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- $HOME/.netrc - Specify automatic login information
- $HOME/.rhosts - Defines which client USERS are NOT required to supply a login password
- ping - Sends an ICMP ECHO_REQUEST
- finger - Lists the current users logged on
- iptrace - Debug trace utility for ip packets
- ipreport - Generates a packet trace report
- spray - Sends a specified number of packets
- no - Configures network options
- netstat - Show network statistics
- nfsstat - Lists statistics about network file system
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Subnet Mask Addressing
Assume a configuration as follows...
SOURCE ADDR = 128.100.0.1
DESTINATION ADDR = 128.100.69.100
SUBNET MASK = 255.255.255.0
BROADCAST MASK = 128.100.0.255
In this case, the DESTINATION PACKET will go to the DEFAULT GATEWAY ADDRESS
Assume a configuration as follows...
SOURCE ADDR = 128.100.0.1
DESTINATION ADDR = 128.100.69.100
SUBNET MASK = 255.255.0.0
BROADCAST MASK = 128.100.255.255
In this case, the DESTINATION PACKET will NOT go to the
DEFAULT GATEWAY ADDRESS and will be routed within the local network.
To determine via the SUBNET MASK if a destination packet goes to the GATEWAY node or not, follow these simple rules:
- Perform a LOGICAL AND of the destination address of the mask of the local subnet address
- Perform an EXCLUSIVE OR on the result of the previous operation and
the local net address of the local interface (eg., source address)
- If the result of the previous operation is a ZERO, the destination is assummed to be reachable directly through one of the local
interfaces ELSE the packet is forwarded to the DEFAULT GATEWAY ADDRESS.
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$HOME/.netrc
Automatic login information for the ftp and rexec commands.
syntax: machine <hostname> login
<username> password <password>
If this file contains a password entry (optional), the
file permissions must be set to 600 (rw for owner only)
or else the error message rshd: 0826-813 Permission is denied is generated.
The file .netrc must exist on the client that your executing the ftp or rexec
command from and the <hostname> must specify the name of server to connect to.
For FTP only, you can initiate file transfers via a macro definition (up to
16 macros can be defined). This file resides on the client machine.
An example of the contents of a .netrc file...
machine sys8 login transfer password now macdef init
get /tmp/database.log /tmp/log/database.log
quit
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$HOME/.rhosts
Defines which client users are not required to supply a login
password for the rcp, rlogin, or rsh commands using a user
account on the server. The file resides on the server machine
under the home directory of the user account being logged into. An ALIAS entry cannot be specified.
syntax: <hostname> <username>
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/etc/hosts.equiv
Defines which clients are permitted to execute commands by the lpd, rlogind,
rcpd, or rshd daemons without supplying a password.
syntax: <hostname>
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/etc/hosts.lpd
Defines which clients are permitted to print jobs to the print server.
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arp - Address Resolution Protocol
Displays the translation table between TCP/IP addresses and network addresses. This physical address is six bytes long and is unique for every
network board. The first three bytes of the address represent a vendor's ID. The last three bytes are assigned by the manufacturer.
Some examples...
NOVELL 00 00 1B
NOVELL 08 00 14
3COM 02 60 8C
SUN 08 00 20
IBM 08 00 5a
DEC AA 00 04
Note that an IP address is really assigned to a network interface and
not a host. A host may have more than 1 network interface as illustrated by the output of the netstat -i command.
Useful tool for debugging network problems.
- For example, if you are using the DOS SERVER daemons to connect PCs to the
RS/6000 and connections aren't being made, check the arp table
to see if there is a hostname entry for the name of the PC you
are connecting from. If there is an entry in the arp table,
then you know that packets are getting across and the problem lies with the DOS SERVER or PC DOS CLIENT software.
- Further, you may have configured two or more hosts with the same internet
address. If this is the case, its possbile that one connection
may get hung. That's because the entry in your arp table gets
overwritten by the new connection. View the arp table and you'll
find that the internet address may now be bound to a new physical
network address. The connection that is hung, will not show
the correct physical address for that IP address. It shows the
new physical address of the machine that has the same IP address of the previous connection.
- Another reason to use this utility for a debugging tool is to show what
network adapter card address is mapped to an internet address. If by chance, you have two nodes on your
network with the same internet address, you will have periodic
problems keeping a connection to one of those two machines until a unique internet address is assigned to each machine.
Examples: arp -a (Displays all addresses that have been translated by the address resolution
protocol.)
Outputs: dospc (193.0.0.8) at 10:0:5a:2b:69:64 [token ring]
eai1 (192.0.0.3) at (incomplete)
An incomplete entry in the network address field means the node in question could not be contacted. Probably reasons are:
- node doesn't exist on the network
- node isn't connected to network
- network is not terminated properly
- problem with network cabling
- software on destination host has a bug
arp -d dospc (Remove the dospc entry from the arp table)
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finger
Lists the current users logged in from remote machines, including username, hostname, idle time, and so on
Example: finger -i (alias f -i)
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host
This command returns the internet address when a hostname is specified or the hostname when the internet address is specified.
| Examples |
What it does |
| host www.ahinc.com |
www.ahinc.com 209.218.236.72 |
| host 209.218.236.72 |
www.ahinc.com 209.218.236.72 |
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hostname
Sets or displays the name of the host system
| Examples |
What it does |
| hostname |
Displays the current hostname value |
| hostname rs520 |
Sets the name of the machine to rs520. Make ure that you set the system
name to rs520 by executing the uname command |
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uname
Sets or displays the system name
| Examples |
What it does |
| uname -S rs520 |
Sets the system name |
| uname -a |
List the system name |
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ifconfig
Configures or displays the network interface parameters for a tcp/ip network
| Examples |
What it does |
| ifconfig en0 |
Indicates if the en0 interface is up and running.
en0:
flags=2000063<UP,BROADCAST,NOTRAILERS,RUNNING,NOECHO>
inet 192.0.0.1 netmask 0xffffff00 broadcast 192.0.0.255 |
| ifconfig en0 up |
Before this command is executed the state of the en0 interface is down (doesn't show UP):
en0: flags=2000062<BROADCAST,NOTRAILERS,RUNNING,NOECHO>
inet 192.0.0.1 netmask 0xffffff00 broadcast 192.0.0.255
After this command is executed the state of the en0 interface is:
en0: flags=2000063<UP,BROADCAST,NOTRAILERS,RUNNING,NOECHO>
inet 192.0.0.1 netmask 0xffffff00 broadcast 192.0.0.255 |
| 1) ifconfig en0 down
2) ifconfig en0 detach |
Adapter statistics for the ethernet card get reset to zero.
See the netstat -v display for further information. |
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iptrace
Debug trace utility for IP packets
| Examples |
What it does |
| iptrace -a -s 193.0.0.1 -i en0 network.log |
All TCP/IP packets that originate from host address of 193.0.0.1
with a ethernet network interface (en0) will be logged to the file network.log. |
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ipreport
Generates a packet trace report generated from the iptrace facility
Example: ipreport network.log
Dumps the packets that were trapped from the iptrace
session in ascii format for inspection. Must
kill the iptrace process before this report can be displayed.
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nameserver (resolv.conf)
| Examples |
What it does |
host ahinc or
arp -a |
If the arp -a or host
commands hang, usually means the name server daemon (/etc/named)
is not running. Use the command ps -ef|grep named to check if named is running. |
| Telnet login responce is very slow. |
Make sure the /etc/resolv.conf file has a valid entry
in it and the /etc/hosts file has the appropriate entries for all known client nodes.
Contents of an example of a /etc/resolv.conf:
nameserver 192.168.1.1 domain ahinc.com
When using the named process, each node should have at least
the loopback and local host name defined in the /etc/hosts file.
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netstat
Shows network statistics
| Examples |
What it does |
| netstat -f inet |
List statistics of AF_INET address family for remote communications |
| netstat -f unix |
List statistics of AF_UNIX address family for local communications. |
| netstat -m |
Shows current network interfaces that are up and running.
- If a network interface shows an asterik next to it (en0*),
this means your interface is down. Use the ifconfig
command to bring the network back up.
- If the Ierrs field (input errors) is nonzero, this
means their are no more kernel memory buffers left to
store an incoming frame or indicates a frame error has been detected.
- If the field Coll field has a colllision rate greater
than 1% of the packets sent/received, then a serious network problem exists.
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| netstat -r |
If the non-loopback entry has a G in Flags field (g=gateway),
then the ping command may hang. Change the Flags field
to U only. Make sure the ROUTED
daemon is running. To start: startsrc -s routed. |
| netstat -nr |
Route Tree for Protocol Family 2: |
netstat -sr
netstat -s |
Displays statistics for each protocol (ip, icmp, tcp, udp) |
| netstat -v |
Shows statistics about network interface cards installed.
- If the Xmit Carrier Lost field contains a non-zero
value, you most likely have a problem with your ethernet cable.
- The errpt command should
contain entries for the eth?
device where
- ? is=first ethernet adapter
- 2=second ethernet adapter, etc
- These error entries should cycle between ENT_ERR6 and ENT_ERR2
and reference problems with the ethernet cable itself.
- Use the ping command to
further identify the problem and also validate through diagnostics that the network adapter card is good.
- XMIT MAX COLLISIONS gets bumped when the transmitter has tried
to transmit a frame 16 times and each of the 16 failed due to a collision.
- XMIT UNDERRUN gets bumped when the transmitter is getting under-runs.
- XMIT TIMEOUTS gets bumped when the transmitter on the adapter times out while trying to transmit.
- PACKETS TOO LONG get bumped when a packet is detected that is
larger than the interface can handle (en0 of 1514+ bytes)
- RECEIVE DMA LOCKUPS gets bumped when the adapter card has detected itself in a lockup state. The microcode will then restart
the 82586 to correct this problem and get things working again.
- INTERRUPTS LOST is the number of interrupts which are not caught
by that NIC device driver. When this counter is not 0, a problem exists with the device driver or NIC.
- NO MBUF ERRORS is the number of failed receive MBUF requests from the NIC device driver.
- RECV OVERRUN COUNT is stating the the NIC is getting overrun.
This is not a big problem unless you see many of these. New microcode/EPROMS may reduce this number.
- RECV PKTS DISCARDED is stating packets are being received that
can't be matched to the TYPE field. For Ethernet cards, the type of frames being received would only be 802.3/Ethernet
Ver 2.0
- PACKETS REJECTED NO NETID is stating that a packet came in at the LLC level and it didn't have a SAP bound to send it
up to. In other words, the device driver didn't recognize the packet type that came in. Could be because your co-existing
with a Novell network using IPX and your using TCP/IP.
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| netstat -v |
chdev -l ent0 -a receive_size=60 |
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nfsstat
Lists statistics about network file system (NFS) and remote procedure calls (RPC).
Also distinguishes between client and server information.
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no
Configures network options. The no command ONLY
operates on the currently running kernel. This command must be run each time the system is rebooted.
| Examples |
What it does |
| no -o tcp_ttl=40 |
Specifies the time to live for TCP packets (40 ticks). |
| no -o thewall=3000 |
Sets the size of the mbuf pool to 3 MB (default is 2 MB). If requests
for mbufs has been denied, this should prevent requests from being denied. |
| no -a ipforwarding=0 |
Turns off IP forwarding |
no -o tcp_sendspace=8192
no -o tcp_recvspace=8192 |
Increasing the buffers to 8k, performance gains of up to 10-20% have been attained. |
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ping
Sends an ICMP ECHO_REQUEST message to a network host every second.
| Examples |
What it does |
| ping rs520 |
Quick way to determine if the network host you wish to communicate
with is either up and running or is configured properly. If
ping intermediately reports back packets (5 packets sent,
1 is lost, 2 packets sent, 1 lost, etc), suspect a bad connection. |
| ping 192.0.0.255 |
Generates responses from all the other nodes connected on a class C
network. If you wish to see what nodes
are up and responding on your network, this is a simple test to run. |
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spray
Sends a specified number of packets over the network and reports back performance statistics.
| Examples |
What it does |
| /usr/etc/spray AIX -c 1000 -l 1400 -d 1 |
Send 1000 packets to the host named AIX with a delay of 1 micro-second,
where each packet sent is 1400 bytes. This uses the RPC protocol. |
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