Port Forwarding Problem Fixed: I am the stupid guy who forgot to enable IP_FORWARD

[Joseph Ollis]

>
> Hi, On Fri, 01 Dec 2006, Joseph Ollis wrote:
>> > I have a workgroup printer in my ltsp edubuntu computer lab(setup with
>> > the default two network cards, one connected to the school lan, and one
>> > connected to the switch for ltsp). I would like to share that printer
>> > with other computers within my school lan. The school computers use the
>> > 10.0.0.* ip addresses and the edubuntu ltsp clients are using the
>> > 192.168.13.*.  I have used iptables before so I tried the following at
>> > our ltsp server.
>> > 
>> > /sbin/iptables -t nat -A PREROUTING -p tcp -i eth0 --dport 9100 -j DNAT --to 192.168.13.234:9100
>> > /sbin/iptables -A FORWARD -p tcp -i eth0 -o eth1 --dport 9100 -j ACCEPT
>> > 
>> > When I tried the printer setup on our XP machines, the setup worked 
>> > well, but would not print the test page. I am not receiving iptables log 
>> > errors in kern.log or dmesg. 
>>     
>
> In what sense did the setup work well if you couldn't print?  ;-) 
>
> Are you definitely printing over jetdirect (ie port 9100)?  If you run
> something like:
> 	tcpdump dst port 9100
> it should show you all packets in and out on port 9100. Using:
> 	tcpdump dst host 192.168.13.234
> you should be able to see the rewritten packets.
>
>   
>> > Does anyone have any thoughts?
>>     
>
> I guess the above should work but could you not just set up a CUPS print
> queue on the Edubuntu server and point the 10.0.0.0/24 machines at the
> edubuntu server?  I guess it adds a bit of a load to edubuntu, but not
> much.  You can also have cups preprocess print jobs.
>
> Gavin

Thanks Gavin, using the tcpdump I figured out that I did not have Port 
Forwarding enabled. I must have run into this problem 5-10 times,and I 
always forget. Anyway, thank you for the help. A good article on how to 
enable IP Forwarding is 
http://www.ducea.com/2006/08/01/how-to-enable-ip-forwarding-in-linux/ .

JO
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