21 comment

1. Hi,
   How to configure squid as a direct connection?
   I would like to following option enable through squid
   1. Username password security with individual site Blocking security.
   2. FTP, SMTP, POP3 etc.. protocol and port configure.
   3. Cache configuration
   4. log maintenance of internet usage, bad site request, downloading, uploading with user name.
   5. firewall configuration to block intruders.(Apart from local user nobody outside the LAN can use our port and connection to the internet
   6. Antivirus : Clamav

2. Prerak

   You are using Red hat Linux…..????

3. – iptables -A INPUT -s -j DROP
   + iptables -A INPUT -s $ip -j DROP

4. Ash,

   PHP treated $ip as PHP variable. But now it is fixed.

   Appreciate your post.

5. Address 127.0.0.0/8 is used by server mail or other server like dns or /etc/hosts. And if was blocked the server no running, how solve it?

6. I think that the following code:,

   # Original code – Start
   SERVER_IP=”202.54.10.20”
   # Add your IP range/IPs here,
   SPOOF_IPS=”0.0.0.0/8 127.0.0.0/8 10.0.0.0/8 172.16.0.0/12 192.168.0.0/16 224.0.0.0/3”
   iptables -A INPUT -s $SERVER_IP -j DROP
   for ip in $SPOOF_IPS
   do
   iptables -A INPUT -s $ip -j DROP
   done
   # Original Code – End

   , can be re-written as :-

   # Suggested Code – Start
   PUBLICIF=eth0
   SERVER_IP=202.54.10.20
   # Add your IP range/IPs here,
   SPOOF_IPS=”$SERVER_IP 0.0.0.0/8 127.0.0.0/8 10.0.0.0/8 172.16.0.0/16 192.168.0.0/16 224.0.0.0/3″
   for ip in $SPOOF_IPS
   do
   iptables -A INPUT -i $PUBLICIF -s $ip -j DROP
   done

   # Suggested code – Stop

   Please correct me if I am wrong, but IMHO, if we DROP packets without mentioning the interface then legitimate connections originating from the same server on loopback (lo) will also get dropped.

   Thanks.

   1. lo is a different interface and is not related to outgoing packets. That’s why it is called the loopback interface. lo should always be accepted for INPUT and OUTPUT. That’s regardless of state; indeed, it is for local connections only (and by local I mean 127.0.0.0/8). Not allowing lo is going to break a lot of services and otherwise cause unexpected results.

7. Sorry. This line:-
   SPOOF_IPS=”$SERVER_IP 0.0.0.0/8 127.0.0.0/8 10.0.0.0/8 172.16.0.0/16 192.168.0.0/16

   Should not contain $SERVER_IP and should instead be:-

   SPOOF_IPS=”0.0.0.0/8 127.0.0.0/8 10.0.0.0/8 172.16.0.0/16 192.168.0.0/16

8. Yes we need to be remove $SERVER_IP from SPOOF_IPS other wise server also block and we do not have any access to server

9. Gunjan,

   The script has been updated to only filter on public interface. This should fix the issue.

10. It is impossible to spoof your address if your Linux computer is behind NAT enabled router such as Cisco.

    This script is more useful on *Linux based router* as packet filtering is one defense against IP spoofing attacks. The Linux gateway to a network usually performs ingress filtering, which is blocking of packets from outside the network with a source address inside the network. This prevents an outside attacker spoofing the address of an internal machine. Ideally the Linux gateway would also perform egress filtering on outgoing packets, which is blocking of packets from inside the network with a source address that is not inside. This prevents an attacker within the network performing filtering from launching IP spoofing attacks against external machines.

    I hope this will help someone.

11. I had to comment out:
    $IPT -A OUTPUT -o $INT_IF -s $SERVER_IP -j $ACTION

    this wouldn’t allow SSH connections out

12. What about when the computer doesn’t have a LAN address, like those directly connected to Internet ?

13. And why manually specify IPtables path when you can use §`which iptables`§ instead ?

14. Hello,

    Please if you can guide me about how can i identify if someone spoofing to my ip ? Which logs should i check ?

15. How do you “call this script from iptables”. What does that mean?

16. How do you “call this script from iptables”. What does that mean?

17. hi, my Linux Email Server(centos 5.7) is giving IP Address Spoofing in N/W.
    am not running any proxy server in that. kept firewall off. now port 25 smtp is giving ip address spoofing with server’s public ip.

    please advice.

18. Something comes to mind (and I admit I’ve been awake since 2 this morning, but…):

    /sbin/iptables -A OUTPUT -o eth1 -s 202.54.10.20 -j DROP

    seems highly suspect to me. If eth1 is the interface connected to the Internet that also has the IP 202.54.10.20 bound to it, then you’re blocking outgoing traffic. Note the OUTPUT chain. The point of blocking spoofed packets and in particular the specific public IP(s) the server (or depending on network: firewall, …) is incoming packets. Outgoing packets would naturally have your node’s IP address, after all (unless we’re talking spoofing and/or not wanting your traffic forwarded by routers, potentially even your ISP’s router [like your default gateway]). It is hosts that are NOT you that are claiming to be you. Your server SHOULD send outbound as its IP (NOT to itself) but should not be sending packets TO itself FROM its IP (that should be blocked).

19. I also have same issue, I think it blocks all output from server to internet

20. Hi,
    Why do you want to block all out going traffic with this rule ?
    $IPT -A OUTPUT -o $INT_IF -s $SERVER_IP -j $ACTION

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