[CentOS] Port Forwarding woes

Barry Brimer lists at brimer.org
Mon Apr 27 11:59:49 UTC 2009


Quoting Bo Lynch <blynch at ameliaschools.com>:

> On Mon, April 27, 2009 12:01 pm, Dan Carl wrote:
> > Bo Lynch wrote:
> >> I'm having some port forwarding issues issues with iptables.
> >> We are using iptables as a firewall with 2 nics and on ip alias.
> >> I'm trying to port forward on the alias ip
> >> eth0 = 65.x.x.1
> >> eth0:1 = 65.x.x.2
> >> eth1 = 192.168.x.x
> >>
> >> I'm wanting to forward certain ports(80,5071...etc) that makes request
> >> on
> >> eth0:1 IP 65.x.x.2 to forward to internal IP 192.168.x.x. I have setup
> >> the
> >> following rules but I must be doing something wrong.
> >> iptables -t nat -A PREROUTING -p tcp -i eth0 -d 65.x.x.2 --dport 80 -j
> >> DNAT --to-destination 192.168.x.x:80
> >> iptables -t nat -A PREROUTING -p tcp -i eth0 -d 65.x.x.2 --dport 5071 -j
> >> DNAT --to-destination 192.168.x.x:5071
> >> iptables -A FORWARD -p tcp -i eth0 -d 192.168.x.x --dport 80 -j ACCEPT
> >> iptables -A FORWARD -p tcp -i eth0 -d 192.168.x.x --dport 5071 -j ACCEPT
> >>
> >> Any help would be greatly appreciated.
> >> Thanks
> >>
> > Try
> >
> > iptables -A FORWARD -p tcp -i eth0 -o eth1 -d 192.168.x.x --dport 80 -j
> > ACCEPT
> > iptables -A FORWARD -p tcp -i eth0 -o eth1 -d 192.168.x.x --dport 5071 -j
> > ACCEPT
> >
> >
> >
> Tried that with no luck. Here is what my NAT looks like.
> [root at localhost ~]# iptables -t nat -L
> Chain PREROUTING (policy ACCEPT)
> target     prot opt source               destination
> DNAT       tcp  --  anywhere             65.161.127.70       tcp dpt:http
> to:192.168.1.3:80
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:powerschool to:192.168.1.3:5071
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:timbuktu to:192.168.1.3:407
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:timbuktu-srv1 to:192.168.1.3:1417
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:timbuktu-srv2 to:192.168.1.3:1418
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:timbuktu-srv3 to:192.168.1.3:1419
> DNAT       tcp  --  anywhere             65.161.127.70       tcp
> dpt:timbuktu-srv4 to:192.168.1.3:1420
> DNAT       tcp  --  anywhere             65.161.127.70       tcp dpt:7880
> to:192.168.1.3:7880
> DNAT       tcp  --  anywhere             65.161.127.70       tcp dpt:https
> to:192.168.1.3:443
> DNAT       udp  --  anywhere             65.161.127.70       udp
> dpt:timbuktu to:192.168.1.3:407
> DNAT       udp  --  anywhere             65.161.127.70       udp
> dpt:timbuktu-srv1 to:192.168.1.3:1417
> DNAT       udp  --  anywhere             65.161.127.70       udp
> dpt:timbuktu-srv2 to:192.168.1.3:1418
> DNAT       udp  --  anywhere             65.161.127.70       udp
> dpt:timbuktu-srv3 to:192.168.1.3:1419
> DNAT       udp  --  anywhere             65.161.127.70       udp
> dpt:timbuktu-srv4 to:192.168.1.3:1420
> DNAT       udp  --  anywhere             65.161.127.70       udp dpt:7880
> to:192.168.1.3:7880
>
> To me it looks like it should work. When I try and do a telnet on the port
> number I get a connection refused. Is using an alias a problem?

Do you have ip forwarding enabled?  Does 'cat /proc/sys/net/ipv4/ip_forward'
show 1 or 0?  Is there a service listening on the port you are forwarding to,
and can you get to this service from a machine on the internal network?


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