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Testing HTTP over telnet:
telnet www.google.com 80
GET / HTTP/1.1

GET /search?q=telnet HTTP/1.1
host: www.google.com
Testing HTTP over OpenSSL:
openssl s_client -connect www.google.com:443
GET /search?q=openssl HTTP/1.1
Common commands:
ifconfig
ping 8.8.8.8
traceroute 8.8.8.8
nslookup google.com
netstat (on OSX:  sudo lsof -i -P)
netstat -an | grep LISTEN
netstat -r
hostname
Links:

http://whois.arin.net/

http://www.whatismyip.com/

https://dnsleaktest.com/

Network (JC)

  • Find FQDN (DNS): cat /etc/hosts

  • Network usage by port, avg: iftop -B

  • Network usage by exe: nethogs

  • Find network interface speed: dmesg | grep -i "is Up"

  • Network ports open by program (OSX): sudo lsof -i

  • SSH port forward (server to client): ssh user@host -L 3306:localhost:3306

  • SSH X-11 forwarding setup for CentOS server:

    Edit /etc/ssh/sshd_config : enable "X11Forwarding"

     yum install xorg-x11-xauth dbus-x11 liberation-*-fonts gnome-icon-theme

  • SSH X-11 forwarding setup for Ubuntu server:

    Edit /etc/ssh/sshd_config : enable "X11Forwarding"

     apt-get install xbase-clients gnome-icon-theme

  • Show all firewall ports open/closed: sudo iptables -L -v -n --line-numbers

  • Add firewall exception:

    1. Allow SSH: iptables -A INPUT -s 0/0 -d 0/0 -p TCP -j ACCEPT --dport ssh
    2. Allow response to requests:iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT
    3. Allow loopback: iptables -v -A INPUT -i lo -j ACCEPT
    4. Allow pinging: iptables -A INPUT -p icmp --icmp-type 8 -j ACCEPT
    5. Allow http: iptables -A INPUT -p tcp --dport http -j ACCEPT
    6. Allow https: iptables -A INPUT -p tcp --dport https -j ACCEPT
    7. Change default to DROP: iptables -P INPUT DROP
    8. Remove REJECT ALL: iptables -D INPUT -s 0/0 -d 0/0 -j REJECT --reject-with icmp-host-prohibited
    9. Save settings:

      • CentOS: service iptables save

      • Ubuntu:

         sudo apt-get install iptables-persistent
 sudo service iptables-persistent start
 sudo bash -c "iptables-save > /etc/iptables/rules"