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networkingTools.md

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Tools used for networking.

sudo apt-get update && sudo apt-get upgrade
sudo apt-get install netcat-openbsd tcpdump traceroute mtr
unix windows use
ifconfig / route ifconfig View the system's network configuration
grep findstr Search for specific text
netstat netstat Display established network connections and statistics
lsof What processes open which files
route Display where and change how traffic is sent
tcpdump Display traffic to and from a server, view network activity
traceroute tracert Show the route the traffic takes
host nslookup Explore the Domain Name System (DNS)

Public (WAN) IP address

curl ipinfo.io/ip
curl ipecho.net/plain
curl ifconfig.me
curl icanhazip.com

Private/Local (LAN) IP address

PC's don't have IP addresses. Network interfaces have them, meaning one PC will have multiple IP addresses.

  1. Find IP address of PC.
ip addr
ip -c addr
ip -o -c addr

# IP address: 192.168.100.16/24
# /24 = 255.255.255.0 subnet mask
  1. Scan subnet for other devices (IP addresses).
nmap -sn 192.168.100.0/24
  1. Ping other device.
ping 192.168.100.10
  1. Default gateway (router)
ip route show
route -n
netstat -rn

Interfaces

ls /sys/class/net/
netstat -i
ip link show

ping

It sends individual packets to test if traffic can get from one address to another, and back.

ping 8.8.8.8

# send 5 packets
ping -c 5 google.com

unknown host

sudo vim /etc/resolv.conf
# Add nameserver 8.8.8.8

lsof

The lsof utility lists open files, including network sockets (listening or connected).

# List only network sockets
lsof -i

nc / netcat

netcat is a tool for manually talking to servers, by connecting to a port and sending a string over it. It's a thin wrapper over TCP.

nc en.wikipedia.org 80
nc localhost 22
nc gmail-smtp-in.l.google.com 80

To illustrate, we can use two terminals to talk to each other. This is a simple TCP server.

Anything typed at the second console will be concatenated to the first, and vice-versa.

The connection is closed with CTRL + d.

# terminal 1 - Listen for an incoming connection on port 6666
nc -l 6666
# typed: foo
# shown: bar

# terminal 2 - Connect to the machine on that listening port
nc 127.0.0.1 6666
# show: foo
# typed: bar

Commands can be sent via a pipe.

echo 'message' | netcat server 80

netcat doesn't know anything about forming HTTP request, but in combination with printf and piping, it can be done.

# Google
printf 'HEAD / HTTP/1.1\r\nHost: google.com\r\n\r\n' | nc google.com 80

# JSON
printf 'GET /posts/1 HTTP/1.1\r\nHost:jsonplaceholder.typicode.com\r\n\r\n' | nc jsonplaceholder.typicode.com 80

host

Used for looking up records in the DNS.

# Returns all the records
host google.com

# Returns just the A record
host -t a google.com

dig

Similar to host in showing DNS records, but in a way more readable for scripts and closer to the way they are stored in the DNS configuration files.

dig google.com

Static server

This will start a static web server on port 8000. The command has to be run in the directory with the index.html file.

python -m SimpleHTTPServer 8080

ifconfig - Check IP address.
ping 8.8.8.8 - Ping IP address.
netstat -tupln - Check open ports.

cat etc/network/interfaces - Shows the interfaces brought up after booting.

/etc/hosts is used to simulate a domain for an IP address. Add 127.0.0.1 domain.com to avoid typing the IP address.

tshark

The terminal version of Wireshark, used for packet sniffing.

traceroute

The asterisks you're seeing are servers that your packets are being routed through whom are timing out (5.0+ seconds) and so traceroute defaults to printing the *.