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Full Discussion: Routing ICMP echo requests
Special Forums IP Networking Routing ICMP echo requests Post 302949421 by dschlic1 on Friday 10th of July 2015 12:04:12 PM
Old 07-10-2015
Routing ICMP echo requests

I have an application where I need to configure a router to pass through ping requests (ICMP type Image through to the LAN port. I have a Linksys WRT54GS with tiny DD-WRT V24 SP2 installed. I am adding the following iptables rules:
Code:
iptables -t nat -I PREROUTING -p icmp --icmp-type 8 -s 72.64.140.50 -j DNAT --to-destination 192.168.1.200 

iptables -t filter -I FORWARD -p icmp --icmp-type 8 -s 72.64.140.50 -d 192.168.1.200 -j ACCEPT 

iptables -t nat -I POSTROUTING -p icmp --icmp-type 8 -s 72.64.140.50 -d 192.168.1.200 -j ACCEPT

The intent is that the first rule will change an incoming echo request destination to the unit on the LAN which I want to receive the ping request.

The second rule allows the modified echo request to pass through the FORWARD table.

And the last one allows the modified echo request to pass through the POSTROUTING table.

When I send a ping to the router with four tries, I get no pings out the LAN. Using iptables -L -v -n I can see were rule #1 passes one packet (but not four), rule #2 passes four packets (good!) and rule #3 passes 1 packet.

At this point I am at loss as to why this is not working. Can someone help me out here?

Last edited by Don Cragun; 07-10-2015 at 04:56 PM.. Reason: Add CODE tags.
 

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IPTABLES-XML(8) 														   IPTABLES-XML(8)

NAME
iptables-xml -- Convert iptables-save format to XML SYNOPSIS
iptables-xml [-c] [-v] DESCRIPTION
iptables-xml is used to convert the output of iptables-save into an easily manipulatable XML format to STDOUT. Use I/O-redirection pro- vided by your shell to write to a file. -c, --combine combine consecutive rules with the same matches but different targets. iptables does not currently support more than one target per match, so this simulates that by collecting the targets from consecutive iptables rules into one action tag, but only when the rule matches are identical. Terminating actions like RETURN, DROP, ACCEPT and QUEUE are not combined with subsequent targets. -v, --verbose Output xml comments containing the iptables line from which the XML is derived iptables-xml does a mechanistic conversion to a very expressive xml format; the only semantic considerations are for -g and -j targets in order to discriminate between <call> <goto> and <nane-of-target> as it helps xml processing scripts if they can tell the difference between a target like SNAT and another chain. Some sample output is: <iptables-rules> <table name="mangle"> <chain name="PREROUTING" policy="ACCEPT" packet-count="63436" byte-count="7137573"> <rule> <conditions> <match> <p>tcp</p> </match> <tcp> <sport>8443</sport> </tcp> </conditions> <actions> <call> <check_ip/> </call> <ACCEPT/> </actions> </rule> </chain> </table> </iptables-rules> Conversion from XML to iptables-save format may be done using the iptables.xslt script and xsltproc, or a custom program using libxsltproc or similar; in this fashion: xsltproc iptables.xslt my-iptables.xml | iptables-restore BUGS
None known as of iptables-1.3.7 release AUTHOR
Sam Liddicott <azez@ufomechanic.net> SEE ALSO
iptables-save(8), iptables-restore(8), iptables(8) Jul 16, 2007 IPTABLES-XML(8)
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