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iprange

Someone recently asked me a question:

How can I save time and script size by specifying a range of IP addresses or ports using iptables?

In old version of iptables IP address ranges are only valid in the nat table (see below for example). However newer version does support option that allows you to specify a range of IP addresses or ports for regular tables such as input.

Iptables set range of IP addresses

You need to use following options with match extensions (-m Ext).

iprange : This matches on a given arbitrary range of IPv4 addresses.

  • [!]--src-range ip-ip: Match source IP in the specified range.
  • [!]--dst-range ip-ip: Match destination IP in the specified range.

Syntax:

-m iprange --src-range IP-IP -j ACTION
-m iprange --dst-range IP-IP -j ACTION

For example, allow incoming request on a port 22 for source IP in the 192.168.1.100-192.168.1.200 range only. You need to add something as follows to your iptables script:

iptables -A INPUT -p tcp --destination-port 22 -m iprange --src-range 192.168.1.100-192.168.1.200 -j ACCEPT  

Port range

if --protocol tcp (-p tcp) is specified, you can specify source port range with following syntax:

  • --source-port port:port
  • --sport port:port

And destination port range specification with following option :

  • --destination-port port:port
  • --dport port:port

For example block lock all incoming ssh access at port 22, for source port range 513:65535:

iptables -A INPUT -p tcp -s 0/0 --sport 513:65535 -d 195.55.55.78 --dport 22 -m state --state NEW,ESTABLISHED -j DROP

On the other hand, just allow incoming ssh request with following port range:

iptables -A INPUT -p tcp -s 0/0 -d 195.55.55.78 --sport 513:65535 --dport 22 -m state --state NEW,ESTABLISHED -j ACCEPT
iptables -A OUTPUT -p tcp -s 195.55.55.78 -d 0/0 --sport 22 --dport 513:65535 -m state --state ESTABLISHED -j ACCEPT

NAT table - range option

If you are using NAT table use options --to-source and --to-destination. For example IP address range:

iptables -t nat -A POSTROUTING -j SNAT --to-source 192.168.1.100-192.168.1.200

ALTERNATIVELY, try range of ports:

iptables -t nat -A POSTROUTING -j SNAT --to-source 192.168.1.100:2000-3000

Read man page of iptables for more information.