Network Topics

Front 1

/etc/hostname

Back 1

Debian/Ubuntu hostname location

Front 2

/etc/sysconfig/network

Back 2

Hostname location for RPM-based distributions

Front 3

hostname

Back 3

Will display the current hostname of the system.

You can optionally pass a new hostname to the command, and it will allow a change of hostname on the system during the current session only.

Front 4

uname -a, uname -n

Back 4

These commands will display the hostname information, and are universal across distributions.

Front 5

127.0.1.1

Back 5

When changing a hostname on Ubuntu you must also change the local call back hostname designated by this IP.

Front 6

ifconfig -a

Back 6

Displays a summary listing of all interfaces.

Front 7

ifconfig {interface} down

Back 7

Administratively brings down an interface.

Interface can be PPP, serial, ethernet, VPN, lo, etc.

Will only work on running and/or configured interfaces.

Front 8

ifconfig {interface} up

Back 8

Brings up an interface that was previously brought down administratively. Must be done from a console.

Interface can be PPP, serial, ethernet, VPN, lo, etc.

Will only work on running and/or configured interfaces.

Front 9

ifdown -a

Back 9

Will bring down all interfaces.

Front 10

ifup -a

Back 10

Will bring up all interfaces.

Front 11

/etc/network/{interface}

Back 11

This is the file location for the network interfaces on a Debian-based system (Debian/Ubuntu).

Front 12

Sample Configuration for eth0 on Debian

Back 12

auto eth0

iface eth0 inet static

address {IP address}

netmask {subnet mask}

network {network address}

broadcast {broadcast address}

gateway {default gw address}

dns-nameservers {nameservers}

Front 13

/etc/sysconfig/network-scripts/{interface}

Back 13

This is the file location for the network interfaces on a RPM-based system (CentOS/RHEL).

Front 14

Sample Configuration for eth0 on CentOS/RHEL

Back 14

DEVICE=eth0

BOOTPROTO=static

ONBOOT=yes

HWADDR={MAC address}

IPADDR={IP address}

NETMASK={subnet mask}

GATEWAY={default gateway}

TYPE=Ethernet

Front 15

route -n

Back 15

Used to view routing information and skip name resolution.

Front 16

netstat -rn

Back 16

Alternate way to view routing information without performing name resolution.

Front 17

sudo route add default gw {gateway IP}

Back 17

Command to add a default gateway route.

Front 18

sudo route del default gw {gateway IP}

Back 18

Command to remove a default gateway route.

Front 19

sudo route add -host {IP} reject

Back 19

Command to reject access to a host/network despite a default route to that network being available.

Front 20

sudo route del -host {IP} reject

Back 20

Command to remove a route rejecting access.

Front 21

sudo route add -net {network address} netmask {subnet mask} gw {default gateway address}

Back 21

This command will add access to a network with no default gateway, or specify a different gateway to use to access a network.

Front 22

/etc/resolv.conf

Back 22

This is the distribution independent location for information about nameservers.

Front 23

/etc/resolv.conf in RPM-based distributions

Back 23

In an RPM-based distribution you can simply edit this file to add information about DNS/nameservers, and it will carry changes between sessions.

Front 24

/etc/resolvconf/resolveconf.d

Back 24

In a Debian-based distribution you can edit /etc/resolv.conf, but the configuration will be overwritten on reboot. Instead you must edit the files in this directory.

Front 25

resolveconf -u

Back 25

Command to update (rebuild) namesevrer information in a Debian-based distribution after making changes.

Front 26

/etc/nsswitch.conf

Back 26

File contains a list of system databases and name service configurations.

This file is associated with the name service caching daemon (nscd), though nscd does not have to be installed (and often is not).

If nscd is installed, it needs to be restarted whenever changes to this file are made.

Front 27

ICMP

Back 27

Acronym for Internet Control Message Protocol. This is a stateless protocol used to query messages.

Front 28

ping

Back 28

This is a stateless tool that is part of ICMP and is used to send query packets to determine if systems are responding.

It sends a specifically formatted 56byte ICMP packet and expects a specifically formatted 64byte package in return.

Front 29

ping -a

Back 29

This command will beep/flash on some terminals when running a ping command.

Front 30

ping -A

Back 30

This command is the Adaptive ping. It provides a faster ping as packets are sent in sequence, but not waiting for a response.

Front 31

ping -c

Back 31

This command sends a count (#) of packets, and then stops, displaying summary.

Front 32

ping -f

Back 32

This command is commonly referred to as a ping flood, and can only be run by root or someone with sudo access. It will send out as many packets to the destination IP as the network interface will handle.

Front 33

ping -I

Back 33

This command will send a ping with the delay interval specified.

Front 34

ping -n

Back 34

This command will send a ping and return IP information only, does not attempt to do DNS lookups.

Front 35

ping -D

Back 35

This command will print a date/timestamp with each line.

Front 36

ping -q

Back 36

Nothing is printed during this ping command, only summary information is printed once the ping is stopped.

Front 37

ping -w

Back 37

This command sets a deadline - it will only wait a specified number of seconds between each ping SEND waiting for an ACK before moving on.

Front 38

ping -v

Back 38

This command is a verbose ping, and it gives more transmission information than just SEND/ACK.

Front 39

/etc/hosts

Back 39

Universal location of the hosts file, regardless of distribution.

Contains information about hosts and corresponding IPs as well as 'localhost' designations.