Re: icmp forward

[Hinko Kocevar <hinko.kocevar@cetrtapot.si>]

Michele Petrazzo - Unipex srl wrote:
> Hinko Kocevar wrote:
>> Hi all,
>>
>> I'm an absolute beginner on the netfilter stuff, so please bear with
>> me here.
>>
>> We have a device running linux 2.6.19 kernel with iptables installed.
>> It acts
>> a a gateway for a another mobile device that connects to linux device
>> via irda
>> port - ppp connection. I've managed to port forward telnet port to
>> mobile device
>> with the help of this page
>> http://kreiger.linuxgods.com/kiki/?Port+forwarding+with+netfilter.
>> Our customers want to be able to ping the mobile device behind the
>> linux firewall
>> and IMHO it is not possible for ICMP packets to be forwarded since it
>> is a protocol
>> by itself (not a TCP/UDP style service).
>>
>>
>> Is it possible to 'port forward' ICMP requests?
>>
> 
> Sure? Looking at firsts google reply, you can find
> 
> iptables -A FORWARD -p icmp --icmp-type echo-request -j ACCEPT
> iptables -t nat -A PREROUTING -i eth0 -p icmp DNAT --to-destination
> 10.2.1.1
> 

That seems to work goo, but now the gateway can not reply to ICMP packets...

> end so on...
> 
> Or I miss something?

I was expecting a solution where gateway would still see the ICMP requests, too.

I guess I'll use a telnet service on the mobile device in order to check if it is
alive and NAT the port on gateway to high port number eg. 2323 -> mobile device
23.

Best regards,
Hinko

-- 
Hinko Kočevar, OSS developer
ČETRTA POT, d.o.o.
Planina 3, 4000 Kranj, SI EU
tel     ++386 (0) 4 280 66 03
e-mail  hinko.kocevar@cetrtapot.si
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