Freq Used Network Cmds

Linux Networking Related Commands/Knowledge¶

To connect to Internet, proper settings of IP, Netmask, Gateway, DNS IP, and device name are all required.

Linux based on CentOS¶

Linux NIC

Network Interface Card are named like modules in Linux, like eth0 for the first NIC, eth1 for the second NIC, and so on.

• Use dmesg to view specific device info. Like dmesg | grep -in eth
• Use lsmod to view whether the device is loaded by kernel. Like lsmod | grep 1000
• Use modinfo to view details about this device, passing in the device number, like e1000
  • the filename portion is the NIC driver for current Kernel version.
• Use ifconfig to lookup the NIC number for a device.
• write driver for your NIC, see Book2 P113

Linux Networks config files

• /etc/services: sets port number for protocols
• /etc/protocols: defines protocols' related info
• /etc/init.d/networking restart: this is an important script to reset entire network to default
• ifup eth0 (ifdown eth0): a script to turn on or off one of the network device

vim /etc/sysconfig/network-scripts/ifcfg-eth0

DEVICE="eth0" <== device number, must match ifcfg-eth0
HWADDR="08:00:27:71:85:BD" <== NIC address (MAC), can be omitted if having only one NIC
NM_CONTROLLED="no" <== uncontrolled by other software
ONBOOT="yes" <== startup on bootup
BOOTPROTO=none <== can be ''dhcp'' or 'none'
IPADDR=192.168.1.100 <== id address
NETMASK=255.255.255.0 <== subnet mask
GATEWAY=192.168.1.254 <== router
# 重点是上面这几个设定项目,底下的则可以省略的啰!
NETWORK=192.168.1.0 <== first IP of this network segment
BROADCAST=192.168.1.255 <== broadcast IP
MTU=1500 <== max transmition unit

the file /etc/resolv.conf contains information about the IP address of DNS nameserver

the command dig shows which DNS nameserver is used to reach an IP, which is part of a package called bind-utils

change host name

change /etc/sysconfig/network and /etc/hosts

Book2 P123

ADSL configuration

Book2 P124

Access Point

When connecting to a router, in fact you are connecting to its Wireless Access Point(AP)

When you are exposed under multiple AP range, you can detect many APs.

Each AP has a SSID or ESSID for the client to identify the right AP.

lsusb is part of usbutils package, that can show usb devices plugged-in

Linux Networking Commands¶

set on/off IP parameters

ifconfig can directly change IP config for a NIC device.

• ifconfig [interface] [up|down|options]
  • up, down: like the commands below
  • mtu: change mtu value
  • netmask: set subnet mask
  • broadcast: set broadcast address

ifup, ifdown can only turn on/off of the device, not changing its parameters

set router parameters

route is the command to use

• route [-nee]
• route add/del [-net|-host] [ip] netmask [mask]

The command ip is like a combination of ifconfig and route

host to host communication

ping

• ping [options and parameters] IP
  • -c numb: execute ping numb times
  • -n: don't lookup hostname, use IP directly
  • -s numb: the ICMP packet size is numb bytes
  • -t numb: TTL's limit is numb
  • -W numb: numb seconds to wait for respond
  • -M [do|dont]: to test MTU size, do means send a DF(Don't Fragment) flag packet

analyze nodes b/w host to host

traceroute

• traceroute [options and parameters] IP
  • -n: don't lookup hostname, use IP directly
  • -U: use UDP port 33434 to test
  • -I: use ICMP to test
  • -T: use TCP port 80 to test
  • -w numb: numb seconds to wait for respond
  • -p port: use other port to test
  • -i: only used when need to specify which AP to use

view current machine's network stats

netstat

• netstat -[rn] related to router
• netstat -[antulpc] related to network ports
  • -r: show route table
  • -n: don't lookup hostname, use IP directly
  • -a: show all, including tcp/udp/unix socket
  • -t show only TCP connections
  • -u: show only UDP connections
  • -l: show only listening services
  • -p: show PID and Program filename
  • -c: update after N seconds

hostname, hostname lookup

host can give you some host's IP. use host [-a] hostname [server] to get more info

nslookup does similar thing. nslookup [-query=[type]] [hostname|IP]

Remote control¶

terminal and BBS: telnet

telnet can combine with BBS and connect to a remote server. The downside is that it is not encrypted. telnet [host|IP [port]]

FTP file transfer

ftp, lftp, gftp can be used for this purpose. gftp has to be in X window mode

ftp [host|IP] [port] to log in a system. use 'anonymous' to login anonymously. type help for useful commands.

use lftp to call scripts and speed up the process of logging in. Book2 P173

Internet Surfing in Command Mode¶

links

links command allows you to view pure html docs. links URL/path_to_HTML

there is no css styling nor img showing

• some freq-used shortcut:
• h: history of viewing
• g: goto URL
• d: download a URL link's target
• q: quit
• o: option, set preferences
• up/down arrow: move to next anchor
• left/right arrow: move back/forward in pages
• ENTER: like right-click

can use links -dump url > index.html to download an entire page

wget

wget is used to fetch data from web servers. wget [option] URL

• options:
  • --http-user=username
  • --http-password=password
  • --quiet

can also set proxy at /etc/wgetrc

Packet catching¶

tcpdump allows you to intercept packet, analyze its contents. It provides so much information, that is categorized as a hecker software. Must be root to run it.

Book2 P182

wireshark or burp is the equivalent in X window mode