[CentOS] iptables port forwarding

Mon Jun 27 04:15:33 UTC 2011
muiz <muiz at 163.com>

Marian,  I'm very happy you're online :)I think I have try the record you mention just now. And I would like to clear what I have done (the scripts I test):/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 192.168.1.250
echo 1 > /proc/sys/net/ipv4/ip_fowardThen it's not to work!




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

>On Monday 27 June 2011 06:50:27 muiz wrote:
>> 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
>
>Yup, its normal not to work... You got the SNAT rule wrong :)
>
>It should be to the IP of the server that is DOING the forwarding...
>
>so 
>
>/sbin/iptables -t nat -A POSTROUTING -j SNAT -s 192.168.0.0/255.255.255.0 --to 
>192.168.1.250
>
>Marian
>
>> 
>> 
>> 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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