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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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SHOREWALL6-TCFILTER(5)						  [FIXME: manual]					    SHOREWALL6-TCFILTER(5)

NAME
tcfilters - shorewall6 u32 classifier rules file SYNOPSIS
/etc/shorewall6/tcfilters DESCRIPTION
Entries in this file cause packets to be classified for traffic shaping. Beginning with Shorewall 4.4.15, the file may contain entries for both IPv4 and IPv6. By default, all rules apply to IPv6 but that can be changed by inserting a line as follows: IPV4 Following entries apply to IPv4. IPV6 Following entries apply to IPv6 ALL Following entries apply to both IPv4 and IPv6. Each entry is processed twice; once for IPv4 and once for IPv6. The columns in the file are as follows (where the column name is followed by a different name in parentheses, the different name is used in the alternate specification syntax). CLASS - interface:class The name or number of an interface defined in shorewall6-tcdevices[1](5) followed by a class number defined for that interface in shorewall6-tcclasses[2](5). SOURCE - {-|address} Source of the packet. May be a host or network address. DNS names are not allowed. DEST - {-|address}} Destination of the packet. May be a host or network address. DNS names are not allowed. PROTO - {-|protocol-number|protocol-name|all} Protocol. DEST PORT (dport) - [-|port-name-or-number] Optional destination Ports. A Port name (from services(5)) or a port number; if the protocol is icmp, this column is interpreted as the destination icmp-type(s). SOURCE PORT (sport) - [-|port-name-or-number] Optional source port. TOS - [-|tos] Optional - specifies the value of the TOS field. The tos value can be any of the following: o tos-minimize-delay o tos-maximuze-throughput o tos-maximize-reliability o tos-minimize-cost o tos-normal-service o hex-number o hex-number/hex-number The hex-numbers must be exactly two digits (e.g., 0x04)x. LENGTH - [-|number] Optional. Must be a power of 2 between 32 and 8192 inclusive. Packets with a total length that is strictly less than the specified number will match the rule. EXAMPLE
Example 1: Place all 'ping' traffic on interface 1 in class 10. Note that ALL cannot be used because IPv4 ICMP and IPv6 ICMP are two different protocols. #CLASS SOURCE DEST PROTO DEST # PORT IPV4 1:10 0.0.0.0/0 0.0.0.0/0 icmp echo-request 1:10 0.0.0.0/0 0.0.0.0/0 icmp echo-reply IPV6 1:10 ::/0 ::/0 icmp6 echo-request 1:10 ::/0 ::/0 icmp6 echo-reply FILES
/etc/shorewall6/tcfilters SEE ALSO
http://shorewall.net/traffic_shaping.htm http://shorewall.net/MultiISP.html http://shorewall.net/PacketMarking.html NOTES
1. shorewall6-tcdevices http://www.shorewall.net/manpages6/shorewall6-tcdevices.html 2. shorewall6-tcclasses http://www.shorewall.net/manpages6/shorewall6-tcclasses.html [FIXME: source] 06/28/2012 SHOREWALL6-TCFILTER(5)
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