[CentOS] iptables port forwarding

muiz muiz at 163.com
Mon Jun 27 03:50:27 UTC 2011


Dear Marian and all,
  It seems don't works:
/sbin/iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 8080 --to a.b.c.d:8181
/sbin/iptables -t nat -A POSTROUTING -j SNAT -s 192.168.0.0/255.255.255.0 --to a.b.c.d
echo 1 > /proc/sys/net/ipv4/ip_foward


I check the Fedora iptables setting:  /etc/sysconfig/iptables files:
...
:POSTROUTING ACCEPT [0:0]
-A PREROUTING -i eth+ -p tcp --dport 8080 -j DNAT --to-destination a.b.c.d:8080
....
:OUTPUT ACCEPT [0:0]
-A FORWARD -i eth+ -m state --state NEW -m tcp -p tcp -d a.b.c.d --dport 8080 -j ACCEPT


And more rules I add is :
/sbin/iptables -t nat -A POSTROUTING -d  a.b.c.d -p tcp --dport 8080 -j MASQUERADE


Then it works!  But if I don't use system-config-firewall GUI tools, then how?




Thanks very much !



At 2011-06-27,"Marian Marinov" <mm at yuhu.biz> wrote:

>On Monday 27 June 2011 00:08:08 muiz wrote:
>> Thanks  Marian,
>> The server only has one IP. I think I should add more iptables records,
>> only one NAT record is not enough,isit correct?  If yes , then how?
>
>Huh, I'm sorry yes you need a second rule. So the rules are:
>iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 8080 --to a.b.c.d:8181
>iptables -t nat -A POSTROUTING -j SNAT -s local_ip/local_net --to 
>192.168.1.250
>echo 1 > /proc/sys/net/ipv4/ip_foward
>
>The Source NAT(SNAT) rule is needed, cause otherwise the packaets that reach 
>a.b.c.d will be comming from the ip of the local client not 192.168.1.250 and 
>so 192.168.1.250 will never receive the replies from a.b.c.d.
>Since the packets reach the client directly from a.b.c.d, the client will 
>simply disregard them and will wait for packets comming from .1.250.
>
>So the SNAT rule changes the SOURCE IP of the packets to 1.250 so a.b.c.d will 
>return the answares to the right source.
>
>Marian
>
>> 
>> 
>>  2011-06-26 23:38:58,"Marian Marinov" <mm at yuhu.biz> wrote:
>> 
>> >On Sunday 26 June 2011 12:53:07 muiz wrote:
>> >> Dear all,
>> >> 
>> >>   I would like to forward a port to an internet server, but failed. can
>> >>   you
>> >> 
>> >> help me? Server:  eth0: 192.168.1.250, Port: 8080 TCP, CentOS 5.6
>> >> Remote server:   IP: a.b.c.d  Port: 8181
>> >> 
>> >> 
>> >> Forward path:  client1(192.168.1.10) -> 192.168.1.250:8080 (forward) ->
>> >> a.b.c.d  Port: 8181 -----------------------------------------
>> >> In Fedora, I successfully to config the firewall using
>> >> system-config-firewall and iptables command: 1. Run
>> >> system-config-firewall
>> >> 
>> >>  1.1 open local port 8080
>> >>  1.2 add a forward rule: local 8080 to remote a.b.c.d:8181, tcp
>> >> 
>> >> 2. echo 1 > /proc/sys/net/ipv4/ip_foward
>> >> 3. add a iptables rule: /sbin/iptables -t nat -A POSTROUTING -d  a.b.c.d
>> >> -p tcp --dport 8181 -j MASQUERADE That's all.
>> >> 
>> >> 
>> >> 
>> >> 
>> >> Thanks !
>> >
>> >You have to use Destination NAT for the job:
>> >
>> >iptables -t nat -A PREROUTING -j DNAT -p tcp --dport 8080 --to
>> >a.b.c.d:8181 echo 1 > /proc/sys/net/ipv4/ip_foward
>> >
>> >If you have more then one IPs on the local machine its a good idea to
>> >specify the destination -d 192.168.1.250
>> >
>> >Marian
>> 
>> _______________________________________________
>> CentOS mailing list
>> CentOS at centos.org
>> http://lists.centos.org/mailman/listinfo/centos
>
>-- 
>Best regards,
>Marian Marinov
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