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 From:  Brian Degenhardt <bmd at bmdhacks dot com>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  nat failing on simultaneous pings
 Date:  Thu, 22 Jul 2004 19:26:57 -0700
I'm having an issue with NAT when multiple machines on the LAN ping
multiple hosts on the WAN side at the same time.  I've tested this on
m0n0 1.0 and 1.1b16 and both exhibit this behavior.

My setup is this:


As far as m0n0wall configuration is concerned, it's pretty much
vanilla.  I set the devices, set the LAN ip and dhcp range and that's

On both the linux boxes, I run fping -c 1 -w 1 ns1.google.com
ns1.yahoo.com www.ingateusa.com and sleep for 5 seconds.  Basically they
send simultaneous pings to three hosts once a second.

On the WAN side of the m0n0wall box, I've uploaded an run tcpdump via
exec.php, here's what it sees:

02:08:43.250343 > ns1.google.com: icmp: echo request (DF)
02:08:43.302480 > www.ingateusa.com: icmp: echo request
02:08:43.302572 > ns1.yahoo.com: icmp: echo request (DF)
02:08:47.915300 > ns1.google.com: icmp: echo request (DF)
02:08:47.930059 > ns1.yahoo.com: icmp: echo request (DF)
02:08:47.935127 ns1.google.com > icmp: echo reply (DF)
02:08:47.951580 ns1.yahoo.com > icmp: echo reply (DF)
02:08:47.973592 > www.ingateusa.com: icmp: echo request
02:08:47.980707 > ns1.google.com: icmp: echo request (DF)
02:08:47.991093 > ns1.yahoo.com: icmp: echo request (DF)

Note that some packets are not getting NATted?
This seems to be a bug in freebsd but I was wondering if anyone had any
pointers to how to fix it?
Here's some references to one other guy who has seen this problem:


Any advice?