[CentOS] combining iptables parameters

Ryan Lynch ryan.b.lynch at gmail.com
Wed Oct 28 21:29:33 UTC 2009


On Wed, Oct 28, 2009 at 15:32, Marcus Moeller <mail at marcus-moeller.de> wrote:
> is there a way to combine iptables parameters like: iptables -A OUTPUT
> -p UDP & -p TCP -d $IP1 & -d $IP2 ?

Each of those parameters is called a "match", in IPTables-speak. You
can specify multiple matches in one rule, but all matches are combined
with an implicit logical AND. There is no way to get a logical OR
amongst multiple matches in a single rule. If you want OR logic, you
use multiple rules.

So, your example could not work as single rule, because no single IP
packet can be both TCP and UDP, and no single IP packet can have
multiple destination IP addresses. IPTables tries to prevent you from
creating nonsensical rules like that in most situations.

You would have to specify the required match space across multiple
rules, maybe something like this:

  iptables -A OUTPUT -p UDP -d $IP1-j DROP
  iptables -A OUTPUT -p TCP -d $IP1 -j DROP
  iptables -A OUTPUT -p UDP -d $IP2 -j DROP
  iptables -A OUTPUT -p TCP -d $IP2 -j DROP

-Ryan

-- 
Ryan B. Lynch
ryan.b.lynch at gmail.com


More information about the CentOS mailing list