Monthly Archive for May, 2018

Debian 9: permanent iptables rules

Just an example for Debian 9.

1. Install ‘iptables-persistent’ package. Agree during installation the rules to be saved to /etc/iptables/rules.v4 .

2. Add rules (e.g. from console):

iptables -P OUTPUDT DROP
iptables -A OUTPUT -d -j ACCEPT

3. Save rules:

netfilter-persistent save

4. Reboot and enjoy.

5. If you need to add/delete/edit rules, edit /etc/iptables/rules.v4 and then run ‘netfilter-persistent start’ to re-read the file.

SIP flood vs OpenSIPS armed with,, ipset and iptables

Preface: the PIKE module itself blocks SIP requests (just stops sending any replies) in case of flood. This article is about going on – adding flooding IP addresses to ipset for further rejecting any traffic to the OpenSIPS server using iptables.

1. Create an ipset with auto removing addresses after 120 seconds and ability to add comments.

ipset create SIPFLOOD hash:ip timeout 120 comment

2. An iptables rule, which will drop incoming traffic from src IP addresses from created ipset table:

iptables -A INPUT -m set --match-set SIPFLOOD src -j DROP

3. Allow OpenSIPS’ run-user (usually ‘opensips’) executing ‘ipset’ command without a password (add this line to /etc/sudoers using ‘visudo’ command):

opensips ALL= NOPASSWD: /sbin/ipset

4. OpenSIPS configuration.

Part of modules section of config:

#### exec
loadmodule ""

#### antiflood module
loadmodule ""
modparam("pike", "sampling_time_unit", 2)
modparam("pike", "reqs_density_per_unit", 10)
modparam("pike", "remove_latency", 120)

Part of OpenSIPS script, assuming that somebody sends us too much OPTIONS requests:

if(is_method("OPTIONS")) {

    switch($retcode) {
        case -2:    # detected once - simply drop the request
        case -1:    # detected again - ban the IP and drop request
            exec("/usr/bin/sudo ipset -exist add SIPFLOOD $si");

    sl_send_reply("200", "OK");

5. You may test all this with ‘sipp’ tool.

This is for generating 10 requests (-r) in 2 seconds (-rp 2000) and exiting sipp after sending 10 requests (-m):

sipp -r 10 -rp 2000 -m 10 -sf OPTIONS.xml

This – for generating 70 requests (-r) in 2 seconds (-rp 2000) and exiting sipp after sending 70 requests (-m):

sipp -r 70 -rp 2000 -m 70 -sf OPTIONS.xml

The OPTIONS.xml is as follows:

iptables: a rule with expiration

If you need an automated way of deleting iptables rules after some time, use this:

iptables -A INPUT -s -j DROP && { echo "iptables -D INPUT -s -j DROP" | at now + 1 min; }

This rule will be deleted in a 1 minute.