Networking

Links

Top 5 unix network monitoring utilities

Gateway

To find the IP address of your network gateway:

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
192.168.11.0    0.0.0.0         255.255.255.0   U     0      0        0 br0
192.168.122.0   0.0.0.0         255.255.255.0   U     0      0        0 virbr0
169.254.0.0     0.0.0.0         255.255.0.0     U     1000   0        0 br0
0.0.0.0         192.168.11.1    0.0.0.0         UG    100    0        0 br0

Check the line with the UG flag U indicates that route is up and G indicates that it is gateway.

The following command will produce very similar output:

netstat -nr

DNS

The DNS server should be listed in:

/etc/resolv.conf

To view the DNS configuration of a Windows workstation.

Lookup

To lookup the DNS information for a site (including IP address):

dig news.bbc.co.uk

IP

To find the IP address:

ifconfig

To set the IP address, edit the following files:

/etc/network/interfaces
/etc/resolv.conf

hosts

The file:

/etc/hosts

Is normally used in preference to a DNS server. The file is used by the workstation to lookup the IP address for a server and to find the fully qualified name from an alias.

The fully qualified domain name needs to be entered. To leave it out would imply some kind of DNS search as a command would not know if this was a top level domain or a host on the local network.

An example file:

0.0.1       woody.pjdk.co.uk    woody        localhost.localdomain   localhost
10.10.4      weezy.pjdk.co.uk    weezy
10.10.5      buzz.pjdk.co.uk     buzz

Another example file:

127.0.0.1>--localhost
127.0.1.1>--buzz

192.168.11.68   bigbox
192.168.11.69   toybox
192.168.11.73   storagebox
192.168.11.70   openerp-dev

# The following lines are desirable for IPv6 capable hosts
::1     ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts

host is a simple utility for performing DNS lookups. It is normally used to convert names to IP addresses and vice versa:

host mail.yahoo.com

NFS

NFS

nmap

To see which ports are open on a server:

nmap <ip address>

e.g:

nmap 10.10.10.4

telnet

To see if a port is running a service:

telnet <ip address> <port>

e.g:

telnet 10.10.10.4 80

Probably have to close down the telnet window (I don’t know how to close it properly).