Re: Intermittent NAT failure when multiple hosts send UDP packets

[Bernardo Innocenti]

Never mind, it was fixed in 2.6.13, probably by this patch:

  https://lists.netfilter.org/pipermail/netfilter-devel/2004-March/014412.html


Bernardo Innocenti wrote:
> This smells like a bug in UDP ip_nat_proto_udp.c or nearby.
> I'm seeing this on 2.6.12-1.1447_FC4, but code in 2.6.13 is
> still the same.
> 
> I've setup SNAT the usual way:
> 
>  iptables -A POSTROUTING -t nat -o ppp0 -j SNAT --to-source 151.38.19.110
> 
> When multiple clients in the LAN send UDP packets to the same port of
> the same remote host, I see something like this in my /proc/net/ip_conntrack:
> 
>  udp      17 170 src=10.3.3.2 dst=194.185.88.60 sport=5060 dport=5060 src=194.185.88.60 dst=151.38.19.110 sport=5060 dport=5060 [ASSURED] use=1
>  udp      17 29 src=10.3.3.2 dst=212.97.59.76 sport=5060 dport=5060 [UNREPLIED] src=212.97.59.76 dst=151.38.19.110 sport=5060 dport=5060 use=1
>  udp      17 177 src=10.3.3.250 dst=194.185.88.60 sport=5060 dport=5060 src=194.185.88.60 dst=151.38.19.110 sport=5060 dport=1024 [ASSURED] use=1
> 
> In the last line, the destination port has been properly remapped from
> 5060 to 1024 to distingish between incoming packets.
> 
> However, I see packets going out over ppp0 without the source
> address properly rewritten to 151.38.19.110:
> 
>  04:38:28.739514 IP 10.3.3.2.5060 > 194.185.88.60.5060: UDP, length 536
> 
> This doesn't happen when there's just a single host sending to port 5060.
> Sometimes I must restart the interface to trigger this bug.

-- 
  // Bernardo Innocenti - Develer S.r.l., R&D dept.
\X/  http://www.develer.com/

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