There are many variants of the UNIX operating system. The most common are
SunOS, FreeBSD, SCO, and Linux. All of these operating systems have tools that
can be used to troubleshoot network issues. These tools have been covered in
greater detail elsewhere in this curriculum and are mentioned here in the
context of troubleshooting options for transport layer issues on UNIX hosts.
Note that while these tools often have the same name and purpose, the
command line options required to use them vary greatly from platform to
platform. Consult the online manual of the local operating software, using the
command man [tool_name], to get more information
about the command line options of the tool to use.
Almost all newer
versions of UNIX variants support native packet-filtering firewall features.
When troubleshooting transport layer problems with UNIX hosts, network
engineers should be aware of the possibility that the problem could be caused
by the local machine firewall configuration.
There are three common
commands used to configure UNIX firewall features:
- On older UNIX variants using kernel version 2.0, use the
ipfwadm command
- On UNIX variants using kernel version 2.2, use the
ipchains command
- On newer UNIX variants using kernel version 2.4 or later, use the
iptables command
Each new version of the firewall capability has produced a tool with
significantly greater features than its predecessor.
ifconfig Command
The
ifconfig command is a low-level command used to administer
network connections on a UNIX host. This command is used to configure network
layer address and DHCP operation interface design. ifconfig
can also be used to configure data-link layer addressing if the network card
has a configurable MAC address, and is used to enable and disable specific
interfaces.
netstat
Command
netstat on UNIX hosts operates in much the
same way as it does on Windows hosts. On UNIX hosts,
netstat also provides information on current network
connections and sockets and can also filter information displayed.
route Command
The route
command is used to add, delete and manage IP routing information on the UNIX
host.
ip Command
ip
is a command available in some newer UNIX variants. One important capability of
the ip tool is its support for multiple protocols,
including IPv4, IPv6, and IPX.
Telnet
This client can be used
in the same way for UNIX as for Windows hosts to help troubleshoot transport
layer connectivity issues. Another Telnet-like troubleshooting tool is
netcat.