2

I asked many questions about this same subject, for example: here, and here.

The answer said I should set up the rule like this:

iptables -A INPUT -i eth0 -m state --state ESTABLISHED,RELATED -j ACCEPT

Then start adding the rest as follows:

# Dynamic Badguy List. Detect and DROP Bad IPs that try to access port 20000.
# Once they are on the BADGUY list then DROP all packets from them.

iptables -A INPUT -i eth0 -m recent --update --hitcount 5 --seconds 90000 --name BADGUY -j LOG --log-prefix "Port 20000 BAD:" --log-level info
iptables -A INPUT -i eth0 -m recent --update --hitcount 5 --seconds 90000 --name BADGUY -j DROP
iptables -A INPUT -i eth0 -p tcp -m tcp --dport 20000 -m recent --set --name BADGUY -j ACCEPT

I did this exactly, but some IPs can still open 100+ connections per IP, so what is the proper way to limit IP connections?

From which we are particularly interested in:

tcp        0  75981 45.233.22.66:22     77.101.61.108:49746     ESTABLISHED
tcp        0  77442 45.233.22.66:22     77.101.61.108:49866     ESTABLISHED
tcp        0 106643 45.233.22.66:22     77.101.61.108:49662     ESTABLISHED
tcp        0  75826 45.233.22.66:22     77.101.61.108:49727     ESTABLISHED
tcp       97      0 45.233.22.66:22     77.101.61.108:50448     CLOSE_WAIT
tcp        0 105924 45.233.22.66:22     77.101.61.108:49798     ESTABLISHED
tcp        0  77441 45.233.22.66:22     77.101.61.108:49852     ESTABLISHED
tcp        0  77442 45.233.22.66:22     77.101.61.108:49813     ESTABLISHED
tcp        0  75223 45.233.22.66:22     77.101.61.108:49655     ESTABLISHED

and

tcp        0  73838 45.233.22.66:22     212.252.97.90:24457     ESTABLISHED
tcp        0  73502 45.233.22.66:22     212.252.97.90:24101     ESTABLISHED
tcp        0  74848 45.233.22.66:22     212.252.97.90:24397     ESTABLISHED
tcp        0  70703 45.233.22.66:22     212.252.97.90:24315     ESTABLISHED
tcp        0  70620 45.233.22.66:22     212.252.97.90:24292     ESTABLISHED
tcp        0  73501 45.233.22.66:22     212.252.97.90:24362     ESTABLISHED
tcp        0  73500 45.233.22.66:22     212.252.97.90:24122     ESTABLISHED

which seem to be more connections than the hit count rule should have allowed.

here is the iptable vxnl

Chain INPUT (policy ACCEPT 35537 packets, 4077701 bytes)
    pkts      bytes target     prot opt in     out     source               destination
 1939108 97521172 REJECT     tcp  --  *      *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22 flags:0x17/0x02 #conn src/32 > 2 reject-with tcp-reset
 1112785 217196313 ACCEPT     all  --  eth0   *       0.0.0.0/0            0.0.0.0/0            state RELATED,ESTABLISHED
   69985  3510824 LOG        all  --  eth0   *       0.0.0.0/0            0.0.0.0/0            recent: UPDATE seconds: 90000 hit_count: 5 name: BADGUY side: source mask: 255.255.255.255 LOG flags 0 level 6 prefix "Port 22 BAD:"
   69985  3510824 DROP       all  --  eth0   *       0.0.0.0/0            0.0.0.0/0            recent: UPDATE seconds: 90000 hit_count: 5 name: BADGUY side: source mask: 255.255.255.255
  217171 11052690 ACCEPT     tcp  --  eth0   *       0.0.0.0/0            0.0.0.0/0            tcp dpt:22 recent: SET name: BADGUY side: source mask: 255.255.255.255

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
    pkts      bytes target     prot opt in     out     source               destination

Chain OUTPUT (policy ACCEPT 3258297 packets, 496362303 bytes)
    pkts      bytes target     prot opt in     out     source               destination
11
  • I'm not sure it is helping to keep starting new questions. Please look at the packet counters (method given in a comment on another of your questions), to observe how many times the DROP rule is being hit. I assume you repeated the same 3 lines but for port 22 instead of port 20000, and also made a different "BADGUY" list name. If your issue is very bad, your list might be overflowing. Observe with, and for example (using one of my list names, you use your list names) cat /proc/net/xt_recent/BADGUY_EMAIL. If an attempt to make another connection is RELATED, this rule will not catch it. Sep 1 '16 at 0:13
  • @DougSmythies i added the list that you requested before i wasnt able to grab it because attack wasnt happened in the past few days now i added thos attacker ips Sep 15 '16 at 21:48
  • Please, show us the packets counters. Just the same way you did on your other question. We want to observe if the DROP path is ever traversed. I'm not understanding your send queue length. Sep 15 '16 at 23:14
  • @DougSmythies added the vxnl removed the old record because of thread limit is 30000 Sep 16 '16 at 7:11
  • i see that ipb got droped but i dont understand how this work is this block ips that have more than 5 connections ? or its something with packet and how i remove blocked ips ? Sep 16 '16 at 7:46
1

A proposed iptables rule set solution to your viscous DDOS attack is the following script:

#!/bin/sh
FWVER=0.01
#
# Vlark.Lopin rule set. Smythies 2016.09.18 Ver:0.01
#     Attempt to manage severe DDOS attack.
#     Port 20000 should only ever have 2 open
#     connections at a time. If more, ban them.
#
#     If too many SSH attempts, ban them.
#     DROP all other unsolicited input.
#     If ssh port has been moved, adjust rules
#     accordingly.
#
#     Requires a larger (1000) than default (100)
#     xt_recent table size.
#
#     See also:
#     http://askubuntu.com/questions/818524/correctly-limit-ip-connections
#     http://askubuntu.com/questions/808297/i-have-massive-attack-on-port-in-my-server
#     http://askubuntu.com/questions/817478/ip-tables-limit-connetion-per-ip-address-can-be-bypassed
#
#     run as sudo
#

echo "Loading Vlark.Lopin rule set version $FWVER..\n"

# The location of the iptables program
#
IPTABLES=/sbin/iptables

#Setting the EXTERNAL and INTERNAL interfaces and addresses for the network
#
# Vlark.Lopin
EXTIF="eth0"
# Doug
#EXTIF="enp9s0"
UNIVERSE="0.0.0.0/0"

#Clearing any previous configuration
#
echo "  Clearing any existing rules and setting default policies.."
$IPTABLES -P INPUT DROP
$IPTABLES -F INPUT
$IPTABLES -P OUTPUT ACCEPT
$IPTABLES -F OUTPUT
$IPTABLES -P FORWARD ACCEPT
$IPTABLES -F FORWARD
# Otherwise, I can not seem to delete it later on
$IPTABLES -F add-to-connlimit-list
# Delete user defined chains
$IPTABLES -X
# Reset all IPTABLES counters
$IPTABLES -Z

# We want to force load the xt_recent module, so that we override the
# default maximum table size. We want 1000 whereas the default is 100.
# Note: It is unlikely that is needs to be 1000 forever. Once the
# bad guys give up, the attempts will become much less frequent, and
# the table size can probably be reduced to default.
# i.e. this force load segment can be commented out, and then it will
# autoload as required.
#
modprobe xt_recent ip_list_tot=1000

#######################################################################
# USER DEFINED CHAIN SUBROUTINES:
#
# add-to-connlimit-list
# To many connections from an IP address has been detected.
# Add the IP address to the bad guy list, and DROP the packet.
# If desired, comment out the log rule.
$IPTABLES -N add-to-connlimit-list
#$IPTABLES -A add-to-connlimit-list -m recent --update --hitcount 1 --seconds 90000 --name BADGUY_CONN
$IPTABLES -A add-to-connlimit-list -m recent --set --name BADGUY_CONN
$IPTABLES -A add-to-connlimit-list -j LOG --log-prefix "CONNLIMIT_ADD:" --log-level info
$IPTABLES -A add-to-connlimit-list -j DROP

#######################################################################
# INPUT: Incoming traffic from various interfaces.  All rulesets are
#        already flushed and set to a default policy of DROP.
#

# loopback interfaces are valid.
#
$IPTABLES -A INPUT -i lo -s $UNIVERSE -d $UNIVERSE -j ACCEPT

# A NEW TCP connection requires SYN bit set and FIN,RST,ACK reset.
# More importantly, this check might prevent lingering packets from
# a forgotten legitimite connection from getting a valid user on the
# bad guy list
#
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j LOG --log-prefix "NEW TCP no SYN:" --log-level info
$IPTABLES -A INPUT -p tcp ! --syn -m state --state NEW -j REJECT

# Not sure if this one is needed or not
#
$IPTABLES -A INPUT -i $EXTIF -p tcp -m state --state INVALID -j LOG --log-prefix "IINVALID:" --log-level info
$IPTABLES -A INPUT -i $EXTIF -p tcp -m state --state INVALID -j DROP

# Allow any related traffic coming back to the server in.
#
$IPTABLES -A INPUT -i $EXTIF -s $UNIVERSE -m state --state ESTABLISHED,RELATED -j ACCEPT

# external interface, from any source, for any remaining ICMP traffic is valid
# Note: consider to not allow, as this is often how bad guys find you
#
$IPTABLES -A INPUT -i $EXTIF -p ICMP -s $UNIVERSE -j ACCEPT

# Secure Shell on port 22 (Change to whatever port you moved SSH to).
#
# Sometimes I uncomment the next line to simply disable external SSH access.
# Particulalry useful when I am rebooting often, thereby losing my current BADGUY table.
#$IPTABLES -A INPUT -i $EXTIF -m state --state NEW -p tcp -s $UNIVERSE --dport 22 -j DROP

# Dynamic Badguy List. Detect and DROP Bad IPs that do password attacks on SSH.
# Once they are on the BADGUY list then DROP all packets from them.
# Sometimes make the lock time very long. Typically to try to get rid of coordinated attacks from China.
$IPTABLES -A INPUT -i $EXTIF -m recent --update --hitcount 5 --seconds 90000 --name BADGUY_SSH -j LOG --log-prefix "SSH BAD:" --log-level info
$IPTABLES -A INPUT -i $EXTIF -m recent --update --hitcount 5 --seconds 90000 --name BADGUY_SSH -j DROP
$IPTABLES -A INPUT -i $EXTIF -p tcp -m tcp --dport 22 -m recent --set --name BADGUY_SSH -j ACCEPT

# Port 20000. Limit to 2 connections per IP address.
# Otherwise ban them.
# Note: The logging is useful for debugging, but might overwhelm the log files. Comment out the logging rule as required.
#
$IPTABLES -A INPUT -i $EXTIF -m recent --update --hitcount 1 --seconds 90000 --name BADGUY_CONN -j LOG --log-prefix "CONNLIMIT:" --log-level info
$IPTABLES -A INPUT -i $EXTIF -m recent --update --hitcount 1 --seconds 90000 --name BADGUY_CONN -j DROP
$IPTABLES -A INPUT -p tcp --dport 20000 -m connlimit --connlimit-above 2 -j add-to-connlimit-list
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 20000 -j ACCEPT

# port 4 is needed. (Consider doing it the same as the SSH port).
# If UDP is needed, then add it.
#
$IPTABLES -A INPUT -m state --state NEW -p tcp --dport 4 -j ACCEPT

# O.K. at this point, we will DROP the packet, however some will be dropped without logging just to make the log file
# less cluttered.
#
$IPTABLES -A INPUT -i $EXTIF -p udp --dport 33434 -j DROP
$IPTABLES -A INPUT -i $EXTIF -p tcp --dport 23 -j DROP

# If your log file is too cluttered, consdier to comment out this log rule.
# It is useful for debugging, but might overwhlem your log files.
#
$IPTABLES -A INPUT -s $UNIVERSE -d $UNIVERSE -j LOG --log-prefix "ICATCH:" --log-level info
# With a default policy of DROP, the following rule isn't actually neeeded.
$IPTABLES -A INPUT -s $UNIVERSE -d $UNIVERSE -j DROP

echo Vlark.Lopin rule set version $FWVER done.

After debugging this script, and if you want to make loading it automatic when booting, add a pre-up directive to your /etc/network/intefaces file. Here is my file as an example:

# interfaces file for smythies.com 2016.01.30
#       attempt to set local DNS herein, as the method
#       used with the old 12.04 server no longer works.
#
# This file describes the network interfaces available on your system
# and how to activate them. For more information, see interfaces(5).

# The loopback network interface
auto lo
iface lo inet loopback
pre-up /home/doug/init/doug_firewall
dns-nameservers 127.0.0.1

# The primary interface (d-link PCI card)
auto enp4s0
iface enp4s0 inet dhcp

# Local network interface (uses built in ethernet port)
auto enp2s0
iface enp2s0 inet static
  address 192.168.111.1
  network 192.168.111.0
  netmask 255.255.255.0
  broadcast 192.168.111.255

The permissions on my script file are:

$ ls -l /home/doug/init/doug_firewall
-rwxr-xr-x 1 doug doug 61703 Aug 27 15:55 /home/doug/init/doug_firewall

or 755.

38
  • now i have to say that this script is really stable and really can protect servers from ddos well done man Sep 28 '16 at 23:44
  • i have question is this rules will protect also the failover ips ? Oct 19 '16 at 5:17
  • I am not sure, but I do not think so. Give us more details. Oct 19 '16 at 18:43
  • as example i have fail over ips over my dede server as eth0 , eth0:0 , eth0:1 on the network interface can i apply the rules in all of them ? Oct 19 '16 at 23:00
  • @Vlark.Lopin; I do not know. Oct 20 '16 at 3:06

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