Thursday, April 4, 2013

Linux setup default gateway with route command

Route command show and/or manipulate the IP routing table under Linux.

Display default route

# route

Add / setup a new route

The syntax is as follows:
route add default gw {IP-ADDRESS} {INTERFACE-NAME}


For example if your router IP address is 192.168.1.254 type the following command as the root user:
# route add default gw 192.168.1.254 eth0 


OR use hostname such as dsl-router

# route add default gw dsl-router eth0



also you can configure ip address and mask using command line
#ifconfig eht0 x.x.x.x netmask x.x.x.x 

Wednesday, April 3, 2013

25 Most Frequently Used Linux IPTables Rules Examples


 
 
# Modify this file accordingly for your specific requirement.
# 1. Delete all existing rules
iptables -F

# 2. Set default chain policies
iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -P OUTPUT DROP

# 3. Block a specific ip-address
#BLOCK_THIS_IP="x.x.x.x"
#iptables -A INPUT -s "$BLOCK_THIS_IP" -j DROP

# 4. Allow ALL incoming SSH
#iptables -A INPUT -i eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 5. Allow incoming SSH only from a sepcific network
#iptables -A INPUT -i eth0 -p tcp -s 192.168.200.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 6. Allow incoming HTTP
#iptables -A INPUT -i eth0 -p tcp --dport 80 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 80 -m state --state ESTABLISHED -j ACCEPT

# Allow incoming HTTPS
#iptables -A INPUT -i eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A OUTPUT -o eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# 7. MultiPorts (Allow incoming SSH, HTTP, and HTTPS)
iptables -A INPUT -i eth0 -p tcp -m multiport --dports 22,80,443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp -m multiport --sports 22,80,443 -m state --state ESTABLISHED -j ACCEPT

# 8. Allow outgoing SSH
iptables -A OUTPUT -o eth0 -p tcp --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 9. Allow outgoing SSH only to a specific network
#iptables -A OUTPUT -o eth0 -p tcp -d 192.168.101.0/24 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
#iptables -A INPUT -i eth0 -p tcp --sport 22 -m state --state ESTABLISHED -j ACCEPT

# 10. Allow outgoing HTTPS
iptables -A OUTPUT -o eth0 -p tcp --dport 443 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A INPUT -i eth0 -p tcp --sport 443 -m state --state ESTABLISHED -j ACCEPT

# 11. Load balance incoming HTTPS traffic
"#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3
 --packet 0 -j DNAT --to-destination 192.168.1.101:443"
"#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3
 --packet 1 -j DNAT --to-destination 192.168.1.102:443"
"#iptables -A PREROUTING -i eth0 -p tcp --dport 443 -m state --state NEW -m nth --counter 0 --every 3 
--packet 2 -j DNAT --to-destination 192.168.1.103:443"

# 12. Ping from inside to outside
iptables -A OUTPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A INPUT -p icmp --icmp-type echo-reply -j ACCEPT

# 13. Ping from outside to inside
iptables -A INPUT -p icmp --icmp-type echo-request -j ACCEPT
iptables -A OUTPUT -p icmp --icmp-type echo-reply -j ACCEPT

# 14. Allow loopback access
iptables -A INPUT -i lo -j ACCEPT
iptables -A OUTPUT -o lo -j ACCEPT

# 15. Allow packets from internal network to reach external network.
# if eth1 is connected to external network (internet)
# if eth0 is connected to internal network (192.168.1.x)
iptables -A FORWARD -i eth0 -o eth1 -j ACCEPT

# 16. Allow outbound DNS
#iptables -A OUTPUT -p udp -o eth0 --dport 53 -j ACCEPT
#iptables -A INPUT -p udp -i eth0 --sport 53 -j ACCEPT

# 17. Allow NIS Connections
# rpcinfo -p | grep ypbind ; This port is 853 and 850
#iptables -A INPUT -p tcp --dport 111 -j ACCEPT
#iptables -A INPUT -p udp --dport 111 -j ACCEPT
#iptables -A INPUT -p tcp --dport 853 -j ACCEPT
#iptables -A INPUT -p udp --dport 853 -j ACCEPT
#iptables -A INPUT -p tcp --dport 850 -j ACCEPT
#iptables -A INPUT -p udp --dport 850 -j ACCEPT

# 18. Allow rsync from a specific network
iptables -A INPUT -i eth0 -p tcp -s 192.168.101.0/24 --dport 873 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 873 -m state --state ESTABLISHED -j ACCEPT

# 19. Allow MySQL connection only from a specific network
iptables -A INPUT -i eth0 -p tcp -s 192.168.200.0/24 --dport 3306 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 3306 -m state --state ESTABLISHED -j ACCEPT

# 20. Allow Sendmail or Postfix
iptables -A INPUT -i eth0 -p tcp --dport 25 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 25 -m state --state ESTABLISHED -j ACCEPT

# 21. Allow IMAP and IMAPS
iptables -A INPUT -i eth0 -p tcp --dport 143 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 143 -m state --state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp --dport 993 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 993 -m state --state ESTABLISHED -j ACCEPT

# 22. Allow POP3 and POP3S
iptables -A INPUT -i eth0 -p tcp --dport 110 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 110 -m state --state ESTABLISHED -j ACCEPT

iptables -A INPUT -i eth0 -p tcp --dport 995 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 995 -m state --state ESTABLISHED -j ACCEPT

# 23. Prevent DoS attack
iptables -A INPUT -p tcp --dport 80 -m limit --limit 25/minute --limit-burst 100 -j ACCEPT

# 24. Port forwarding 422 to 22
iptables -t nat -A PREROUTING -p tcp -d 192.168.102.37 --dport 422 -j DNAT --to 192.168.102.37:22
iptables -A INPUT -i eth0 -p tcp --dport 422 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -o eth0 -p tcp --sport 422 -m state --state ESTABLISHED -j ACCEPT

# 25. Log dropped packets
iptables -N LOGGING
iptables -A INPUT -j LOGGING
iptables -A LOGGING -m limit --limit 2/min -j LOG --log-prefix "IPTables Packet Dropped: " --log-level 7
iptables -A LOGGING -j DROP

Tuesday, April 2, 2013

URL Redirection Using iptables

We will configure IPTables on a Linux server to redirect all the traffic coming on port 80, (which is the default web server port), to a server with the IP 122.164.34.240. The first step is to set your Linux box to allow this kind of forwarding to take place. Open a terminal window, log in as root user and run the following command:

#vim /etc/sysctl.conf
(add new line)

net.ipv4.ip_forward=1

save and exit

The next step is to tell IPTables to redirect the traffic to the new server:

iptables -t nat -A PREROUTING -p tcp --dport 80 -j DNAT --to-destination 122.164.34.240
  

Here’s where the IPTables magic happens. With the third and final step we tell IPTables to rewrite the origin of connections to the new server’s port 80 to appear to come from the old server.

iptables -t nat -A POSTROUTING -p tcp -d 122.164.34.240 --dport 80 -j MASQUERADE


The final step is required because if we don’t tell the web server of the new server that the connections are coming from the client machines, it would think that they are originating from the old server.
You may want to repeat this for the databases and email server port as well.