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Terminal Commands for Networking

IP Addresses

$ ifconfig
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
	ether f0:18:98:55:ef:d8 
	inet6 fe80::1c6c:449d:1dc9:d60a%en0 prefixlen 64 secured scopeid 0xa 
	inet 192.168.88.162 netmask 0xffffff00 broadcast 192.168.88.255
	nd6 options=201<PERFORMNUD,DAD>
	media: autoselect
	status: active

From the resulting output, find en0 - on later versions of macbooks en0 is usually the AirPort (WiFi).

Typically a machine would have en0, en1, lo0 and some other hardware interfaces:

  • en0: Ethernet 0
  • en1: Ethernet 1
  • lo0: Loopback (localhost)

To see all hardware ports:

$ networksetup -listallhardwareports
Hardware Port: Wi-Fi
Device: en0
Ethernet Address: f0:18:98:55:ef:d8

Hardware Port: Bluetooth PAN
Device: en6
Ethernet Address: f0:18:98:57:c9:71

Hardware Port: Thunderbolt 1
Device: en1
Ethernet Address: 86:00:9d:61:53:01

Our IP address is listed above (192.168.88.162). Alternatively, we can employ a more direct approach:

$ ipconfig getifaddr en0
192.168.88.162

Nameservers Lookup

nslookup will display the actual IP address for the name queried (192.168.88.1) and also the name server used to make the request (in this case: 192.168.88.1).

$ nslookup algorit.ma 
Server:		192.168.88.1
Address:	192.168.88.1#53

Non-authoritative answer:
Name:	algorit.ma
Address: 103.9.100.186

$ nslookup google.com
Server:		192.168.88.1
Address:	192.168.88.1#53

Non-authoritative answer:
Name:	google.com
Address: 172.217.160.46

Ping

$ ping algorit.ma

Scan a network

$ nmap -sn 192.168.88.0/24
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-13 20:47 WIB
Nmap scan report for 192.168.88.1
Host is up (0.019s latency).
Nmap scan report for 192.168.88.160
Host is up (0.029s latency).
Nmap scan report for 192.168.88.162
Host is up (0.0016s latency).
Nmap scan report for 192.168.88.224
Host is up (0.071s latency).
Nmap scan report for 192.168.88.232
Host is up (0.041s latency).
Nmap scan report for 192.168.88.251
Host is up (0.032s latency).
Nmap done: 256 IP addresses (6 hosts up) scanned in 6.81 seconds

Network / Sockets Status on Host Machine

  1. Execute helpers/echo-server.py in one terminal;
  2. While (1) listens for connection open a second terminal; Execute helpers/echo-client.py
  3. Go back to (1) and notice the the printed message: Connected by ('127.0.0.1', 57007). 57007 is the port number for the client socket, not the server socket.
  4. Use netstat -an or lsof -i -n to view socket state
$ netstat -an
Active Internet connections (including servers)
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)   
tcp4       0      0  127.0.0.1.44444        *.*                    LISTEN

If in helpers/echo-server.py we substituted HOST='127.0.0.1' for HOST='' we would expect the Local Address file printed in netstat to be *.44444 instead of 127.0.0.1.44444. When the Local address is *.44444 which means all available host interfaces that support the address family will be used. The tcp4 value in the Proto column tells us that socket.AF_INET was used (IPv4).

$ netstat -anl | grep LISTE

In the above command, we use netstat with the following parameters before passing it to the regex call to search for only LISTENING ports.

Common parameters with netstat:

  • a: List all current connections
  • n: Suppress hostname lookup so host name is unknown and ip address is given. Makes the execution faster by disabling reverse dns lookup
  • l: List only listening ports
  • -p tcp or -p udp for tcp or udp only ports
  • netstat -i: print network interfaces

Example usage:

$ netstat -anl -p tcp | grep 44444 
Proto Recv-Q Send-Q  Local Address          Foreign Address        (state)   
tcp4       0      0  127.0.0.1.44444        *.*                    LISTEN

Another way of seeing this is the lsof command, which stands for "list open files". When used with the i flag, it gives you the COMMAND, PID (process id) and USER (user id) of open Internet sockets.

$ lsof -i -n
COMMAND     PID   USER   FD   TYPE             DEVICE SIZE/OFF NODE NAME
python3.6 22459 samuel    3u  IPv4 0x1af15eb429051673      0t0  TCP 127.0.0.1:44444 (LISTEN)

If we inspect the code in helpers/echo-server.py and know which port to look for as well as the protocol, we can also use nmap to scan for, in this instance, TCP port number 44444 (nmap -p T:44444 127.0.0.1):

$ nmap -p T:44444 127.0.0.1
Starting Nmap 7.70 ( https://nmap.org ) at 2019-03-18 14:09 +08
Nmap scan report for localhost (127.0.0.1)
Host is up (0.00018s latency).

PORT      STATE SERVICE
44444/tcp open  cognex-dataman

Nmap done: 1 IP address (1 host up) scanned in 0.06 seconds