Linux Networking Commands

Networking Commands


List of Linux networking tools

Common System Administrator files and commands

Network Status commands
netstat <seconds> -- running error stats + counts on config interface every N seconds

netstat –a -- socket ports and state

netstat -s protocol (tcp etc.) counts and errors

netstat -r -- routing table dump

netstat –i -- list of interfaces and gives 3 letter interface names

If you use the –n flag, host addressed will be numeric and avoid a DNS lookup,which might be faster in some cases. Combine with the other switches

Network interfaces commands
ifconfig –a -- Show all interfaces

ifconfig <interface name> -- setup for a particular interface, e.g. ln0

ifconfig <interface name> <params> -- Set params of the interface. Root only. Typically IP address, subnet, are set upon bootup in /etc/rc*ROOT ONLY Connectivity.

ping <host> -- send an ICMP echo message (one packet) to a host.This may go continually until you hit Control-C.Ping means a packet was sent from your machine via ICMP, and echoed at the IP level. ping tells you if the OS is up; but doesn't tell you if inetd or other daemons are running.

telnet host <port> -- talk to "hosts" at the given port number. By default, the telnetport is port 23. See the file /etc/services for a list of what services are in use at what ports.A few samples:7 – echo port, use control-] to get out 25 – SMTP, use to send mail 79 - Finger.

telnet ip-number -- Can tell if inetd is functioning. With telnet you can use the ip number instead of the host name. If ip-number as opposed to telnet hostname works, you have problems with the name server. If you can ping, but you can't telnet, you have problems with getting processes running and possibly inetd configuration problems.

Routing
netstat –r -- Print routing tables. The routing tables are stored in the kernel and used by ip to route packets to non-local networks.
route ... params -- The route command is used for setting a static (non-dynamic by hand route) route path in the route tables. It is typically used at boot in the /etc/rc scripts. It can be used for setting a default route; i.e., when in doubt send all packets to a particular local gateway. Generally ROOT ONLY.
routed -- The BSD daemon that does dynamic routing. Started at boot. This runs the RIP routing protocol. ROOT ONLY. You won’t be able to run this without root access.
gated -- Gated is an alternative routing daemon to RIP.It uses the OSPF, EGP, and RIP protocols in one place. ROOT ONLY.
traceroute <host> -- Useful for tracing route of IP packets. The packet causes message to be sent back from all gateways in between the source and destination.
Arp
arp –a -- Print the arp table. Arp is used to translate IP addresses into Ethernet addresses. Root can add and delete arp entries. Deleting them can be useful if an arp entry is malformed or just wrong. Arp entries explicitly added by root are permanent -- they can also be by proxy. The arp table is stored in the kernel and manipulated dynamically. Arp entries are cached and will time out and are deleted normally in 20 minutes.
NFS/NIS - Network file system/yellow pages
df . -- Shows your filesystem and mount for the current directory.
df -t nfs -- Show nfs mounts.
mount -- Use to mount a file system, ROOT ONLY. /etc/fstab contains the mounts done at boot time./etc/exports contains mount points exported on a suste,//etc/mtab contains the mount table built by mount.
Other Useful Commands
ps aux or ps alx -- List of processes in action, usage varies from system to system.“ps -aux | grep “ often useful to filter output by string.
ps -- List your processes in the foreground.
nslookup (or nslookup <host>) -- Makes queries to the DNS server to translate IP to a name, or vice versa.
ftp <host> -- Transfer files to host. Often can use login=“anonymous” , p/w=“guest”.
rcp <switches> system:file system:file -- Rcp performs a remote copy from one system to another, and is used much like Unix cp. Rcp and rsh use rshd which is controlled by inetd. The rshd security protocol is very weak, and uses the .rhosts and /etc/hosts.equiv files. Since security is so weak these protocols are often banned from systems (e.g., add “*” to rhosts and anyone could log into your account).
rsh host <command> --BSD remote shell.
rlogin <host> -l <login> -- Logs into the host with a virtual terminal like telnet.
Important Files

/etc/hosts - names to ip addresses
/etc/networks - network names to ip addresses
/etc/protocols - protocol names to protocol numbers
/etc/services - tcp/udp service names to port numbers
netstat (ss)
Displays contents of /proc/net files. It works with the Linux Network Subsystem, it will tell you what the status of ports are ie. open, closed, waiting, masquerade connections. It will also display various other things. It has many different options.

Netstat (Network Statistic) command display connection info, routing table information etc. To displays routing table information use option as -r.

Sample output:

Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)    
tcp4       0      0  127.0.0.1.62132        127.0.0.1.http        ESTABLISHED
tcp4       0      0  127.0.0.1.http         *                     LISTEN
tcpdump
This is a sniffer, a program that captures packets off a network interface and interprets them for you. It understands all basic internet protocols, and can be used to save entire packets for later inspection.

ping
The ping command (named after the sound of an active sonar system) sends echo requests to the host you specify on the command line, and lists the responses received their round trip time. PING (Packet INternet Groper) command is the best way to test connectivity between two nodes. Whether it is Local Area Network (LAN) or Wide Area Network (WAN). Ping use ICMP (Internet Control Message Protocol) to communicate to other devices. You can ping host name of ip address using below command.

$ ping google.com
PING google.com (216.58.198.78): 56 data bytes
64 bytes from 216.58.198.78: icmp_seq=0 ttl=46 time=6.108 ms
64 bytes from 216.58.198.78: icmp_seq=1 ttl=46 time=6.222 ms
^C
--- google.com ping statistics ---
2 packets transmitted, 2 packets received, 0.0% packet loss
round-trip min/avg/max/stddev = 6.108/6.165/6.222/0.057 ms
traceroute
traceroute will show the route of a packet. It attempts to list the series of hosts through which your packets travel on their way to a given destination. Also have a look at xtraceroute (one of several graphical equivalents of this program). traceroute is a network troubleshooting utility which shows number of hops taken to reach destination also determine packets traveling path. Below we are tracing route to global DNS server IP Address and able to reach destination also shows path of that packet is traveling.

$ traceroute -I google.com
traceroute to google.com (216.58.198.78), 128 hops max, 72 byte packets
1  52.93.7.1 (52.93.7.1)  6.361 ms  6.229 ms  6.106 ms
2  72.14.215.85 (72.14.215.85)  5.939 ms  5.460 ms  5.914 ms
3  209.85.252.198 (209.85.252.198)  6.012 ms  5.694 ms  5.761 ms
4  64.233.174.27 (64.233.174.27)  5.079 ms  4.776 ms  4.662 ms
5  dub08s02-in-f78.1e100.net (216.58.198.78)  6.650 ms  5.509 ms  5.596 ms
tracepath
tracepath performs a very simlar function to traceroute the main difference is that tracepath doesn't take complicated options.

nmap
“ network exploration tool and security scanner”. nmap is a very advanced network tool used to query machines (local or remote) as to whether they are up and what ports are open on these machines. Some features only activate when Nmap is run with privileges. More information: https://nmap.org.

# Try to determine whether the specified hosts are up and what are their names:
nmap -sn {{ip_or_hostname}} {{optional_another_address}}

# Like above, but also run a default 1000-port TCP scan if host seems up:
nmap {{ip_or_hostname}} {{optional_another_address}}

# Also enable scripts, service detection, OS fingerprinting and traceroute:
nmap -A {{address_or_addresses}}

# Assume good network connection and speed up execution:
nmap -T4 {{address_or_addresses}}

# Scan a specific list of ports (use -p- for all ports 1-65535):
nmap -p {{port1,port2,…,portN}} {{address_or_addresses}}

# Perform TCP and UDP scanning (use -sU for UDP only, -sZ for SCTP, -sO for IP):
nmap -sSU {{address_or_addresses}}

# Perform TLS cipher scan against a host to determine supported ciphers and SSL/TLS protocols:
nmap --script ssl-enum-ciphers {{address_or_addresses}} -p 443

# Perform full port, service, version detection scan with all default NSE scripts active against a host to determin weaknesses and info:
nmap -sC -sV {{address_or_addresses}}

dig
Dig (domain information groper) query DNS related information like A Record, CNAME, MX Record etc. This command mainly use to troubleshoot DNS related query.

$ dig amazon.com

; <<>> DiG 9.8.3-P1 <<>> amazon.com
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 30832
;; flags: qr rd ra; QUERY: 1, ANSWER: 6, AUTHORITY: 0, ADDITIONAL: 0

;; QUESTION SECTION:
;amazon.com.			IN	A

;; ANSWER SECTION:
amazon.com.		17	IN	A	54.239.25.200
amazon.com.		17	IN	A	54.239.25.208
amazon.com.		17	IN	A	54.239.26.128
amazon.com.		17	IN	A	54.239.17.6
amazon.com.		17	IN	A	54.239.17.7
amazon.com.		17	IN	A	54.239.25.192

;; Query time: 3 msec
;; SERVER: 10.78.97.142#53(10.78.97.142)
;; WHEN: Thu Dec 29 13:56:22 2016
;; MSG SIZE  rcvd: 124

nslookup
nslookup command also use to find out DNS related query. The following examples shows A Record (IP Address) of tecmint.com.

nslookup amazon.com
Server:		10.78.97.142
Address:	10.78.97.142#53

Non-authoritative answer:
Name:	amazon.com
Address: 54.239.25.192
Name:	amazon.com
Address: 54.239.25.200
Name:	amazon.com
Address: 54.239.25.208
Name:	amazon.com
Address: 54.239.26.128
Name:	amazon.com
Address: 54.239.17.6
Name:	amazon.com
Address: 54.239.17.7
host
host command to find name to IP or IP to name in IPv4 or IPv6 and also query DNS records.

$ host amazon.com
amazon.com has address 54.239.17.6
amazon.com has address 54.239.17.7
amazon.com has address 54.239.25.192
amazon.com has address 54.239.25.200
amazon.com has address 54.239.25.208
amazon.com has address 54.239.26.128
amazon.com mail is handled by 10 amazon-smtp.amazon.com.
hostname
hostname is to identify in a network. Execute hostname command to see the hostname of your box. You can set hostname permanently in /etc/sysconfig/network. Need to reboot box once set a proper hostname.

$ hostname -f
miglen.development.box
arp
ARP (Address Resolution Protocol) is useful to view / add the contents of the kernel’s ARP tables. To see default table use the command as.

Configuration
ifconfig
This command is used to configure network interfaces, or to display their current configuration. In addition to activating and deactivating interfaces with the “up” and “down” settings, this command is necessary for setting an interface's address information if you don't have the ifcfg script.

ifup - Use ifup device-name to bring an interface up by following a script (which will contain your default networking settings). Simply type ifup and you will get help on using the script.
ifdown - Use ifdown device-name to bring an interface down using a script (which will contain your default network settings). Simply type ifdown and you will get help on using the script.
ifcfg - Use ifcfg to configure a particular interface. Simply type ifcfg to get help on using this script.
route
The route command is the tool used to display or modify the routing table. To add a gateway as the default you would type:

$ route -n
Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
0.0.0.0         172.31.16.1     0.0.0.0         UG    0      0        0 eth0
172.17.0.0      0.0.0.0         255.255.0.0     U     0      0        0 docker0
172.31.16.0     0.0.0.0         255.255.240.0   U     0      0        0 eth0
iwconfig
iwconfig command in Linux is use to configure a wireless network interface. You can see and set the basic Wi-Fi details like SSID channel and encryption. You can refer man page of iwconfig to know more.

ip
$ watch ss -tp                               # Network connections
$ netstat -ant                               # Tcp connections -anu=udp
$ netstat -tulpn                             # Connections with PIDs
$ lsof -i                                    # Established connections
$ smb:// ip /share                           # Access windows smb share
$ share user x.x.x.x c$                      # Mount Windows share
$ smbclient -0 user\\\\ ip \\ share          # SMB connect
$ ifconfig eth# ip / cidr                    # Set IP and netmask
$ ifconfig ethO:l ip / cidr                  # Set virtual interface
$ route add default gw gw_ip                 # Set GW
$ ifconfig eth# mtu [size]                   # Change MTU size
$ export MAC=xx: xx: xx: xx: xx: xx          # Change MAC 
$ ifconfig int hw ether MAC                  # Change MAC
$ macchanger -m MAC int                      # Backtrack MAC changer
$ iwlist int scan                            # Built-in wifi scanner
$ dig -x ip                                  # Domain lookup for IP
$ host ip                                    # Domain lookup for IP
$ host -t SRV _ service _tcp.url.com         # Domain SRV lookup
$ dig @ ip domain -t AXFR                    # DNS Zone Xfer
$ host -l domain namesvr                     # DNS Zone Xfer
$ ip xfrm state list                         # Print existing VPN keys
$ ip addr add ip / cidr dev ethO             # Adds 'hidden' interface
$ /var/log/messages | grep DHCP              # List DHCP assignments
$ tcpkill host ip and port port              # Block ip:port
$ echo "1" /proc/sys/net/ipv4/ip_forward     # Turn on IP Forwarding
$ echo "nameserver x.x.x.x" /etc/resolv.conf # Add DNS Server
arpwatch – Ethernet Activity Monitor.

bmon – bandwidth monitor and rate estimator.

bwm-ng– live network bandwidth monitor.

curl – transferring data with URLs. (or try httpie)

darkstat – captures network traffic, usage statistics.

dhclient – Dynamic Host Configuration Protocol Client

dig – query DNS servers for information.

dstat – replacement for vmstat, iostat, mpstat, netstat and ifstat.

ethtool – utility for controlling network drivers and hardware.

gated – gateway routing daemon.

host – DNS lookup utility.

hping – TCP/IP packet assembler/analyzer.

ibmonitor – shows bandwidth and total data transferred.

ifstat – report network interfaces bandwidth.

iftop – display bandwidth usage.

ip – a command with more features that ifconfig (net-tools).

iperf3 – network bandwidth measurement tool. (above screenshot Stacklinux VPS)

iproute2 – collection of utilities for controlling TCP/IP.

iptables – take control of network traffic.

IPTraf – An IP Network Monitor.

iputils – set of small useful utilities for Linux networking.

iw – a new nl80211 based CLI configuration utility for wireless devices.

jwhois (whois) – client for the whois service.

“lsof -i” – reveal information about your network sockets.

mtr – network diagnostic tool.

net-tools – utilities include: arp, hostname, ifconfig, - netstat, rarp, route, plipconfig, slattach, mii-tool, iptunnel and ipmaddr.

ncat – improved re-implementation of the venerable netcat.

netcat – networking utility for reading/writing network connections.

nethogs – a small ‘net top’ tool.

Netperf – Network bandwidth Testing.

netsniff-ng – Swiss army knife for daily Linux network plumbing.

netstat – Print network connections, routing tables, statistics, etc.

netwatch – monitoring Network Connections.

ngrep – grep applied to the network layer.

nload – display network usage.

nmap – network discovery and security auditing.

nmcli – a command-line tool for controlling NetworkManager and reporting network status.

nmtui – provides a text interface to configure networking by controlling NetworkManager.

nslookup – query Internet name servers interactively.

ping – send icmp echo_request to network hosts.

route – show / manipulate the IP routing table.

slurm – network load monitor.

snort – Network Intrusion Detection and Prevention System.

smokeping – keeps track of your network latency.

socat – establishes two bidirectional byte streams and transfers data between them.

speedometer – Measure and display the rate of data across a network.

speedtest-cli – test internet bandwidth using speedtest.net

ss – utility to investigate sockets.

ssh – secure system administration and file transfers over insecure networks.

tcpdump – command-line packet analyzer.

tcptrack – Displays information about tcp connections on a network interface.

telnet – user interface to the TELNET protocol.

tracepath – very similar function to traceroute.

traceroute – print the route packets trace to network host.

vnStat– network traffic monitor.

websocat – Connection forwarder from/to web sockets to/from usual sockets, in style of socat.

wget – retrieving files using HTTP, HTTPS, FTP and FTPS.

Wireless Tools for Linux – includes iwconfig, iwlist, iwspy, iwpriv and ifrename.

Wireshark – network protocol analyzer.

watch ss -tp -- Network Connec­tions

netstat -ant -- TCP connec­tions

netstat -anu -- UDP Connec­tions

netstat -tulpn -- Connec­tions with PIDs

lsof -i -- Establ­ished Connec­tions

smb:/­/<I­P>/­<SH­ARE­NAM­E> -- Access Windows SMB Share

share <US­ERN­AME> <IP> c$ -- Mount Windows Share

ifconfig <IN­TER­FAC­E> <IP­/CI­DR> -- Set IP and netmask

ifconfig eth0:1 <IP­/CI­DR> -- Set virtual interface

route add default gw <IP­> -- Set Default Gateway

ifconfig <IN­TER­FAC­E> mtu <SI­ZE> -- Change MTU size

export MAC=<M­ACA­DDR­ESS­> -- Change MAC Address

ifconfig int hw ether <MA­CAD­DRE­SS> -- Change MAC Address

dig -x <IP­> -- Domain Lookup IP

host <IP­> -- Domain Lookup IP

dig@<­IP> <DO­MAI­N> -t AXFR -- DNS Zone Transfer

host -l <DO­MAI­N> <NA­MES­ERV­ER> -- DNS Zone Transfer

echo "­1" > /proc/­sys­/ne­t/i­pv4/ip forward -- Enable IP Forwarding

echo <"NA­MES­ERV­ER"> > /etc/r­eso­lv.c­onf -- Add DNS Server