Linux – Block ip forwarding for specific remote ip address

firewalliptableslinuxnetworkingrouting

I use ubuntu as gateway for several hosts. I need advise how to block ip forwarding for specific ip address or specific ip range?

I tried to block ip via ufw deny rules, but it looks like ip forwarding settings cannot be modified via rules and it can be applied only globally (DEFAULT_FORWARD_POLICY in /etc/default/ufw)

Also i tried to change iptables rules directly:

iptables -A FORWARD -j REJECT --reject-with icmp-host-prohibited

After this command ip forwarding reject rule blocks forwarding requests from all of remote hosts.

Update:
current iptable output:

root@mtu90:/home/pi# iptables -L -n -v
Chain INPUT (policy ACCEPT 5671 packets, 927K bytes)
 pkts bytes target     prot opt in     out     source               destination 
    0     0 DROP       all  --  *      *       0.0.0.0/0            172.16.1.77 
  192 15408 DROP       all  --  *      *       172.16.1.77          0.0.0.0/0   

Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
 pkts bytes target     prot opt in     out     source               destination 
  895  136K            all  --  *      *       0.0.0.0/0            0.0.0.0/0   
  518 30999 REJECT     all  --  *      *       0.0.0.0/0            0.0.0.0/0            reject-with icmp-host-prohibited

Chain OUTPUT (policy ACCEPT 119 packets, 14872 bytes)
 pkts bytes target     prot opt in     out     source               destination

Best Answer

I think you are overthinking the problem. It is trivial to block forwarding requests using iptables on whatever basis you like.

There is, of-course, a default setting - forwarding can be allowed or denied by default - Your current setting is allowed. Thus to drop a specific host, simply add an iptables rule

iptables -I FORWARD -d sou.rce.ip.add -j DROP

Make sure that you remember to remove your rule to REJECT everything in the forward chain.

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