packets missing/skipping DNAT rules

packets missing/skipping DNAT rules

[Mr Ritter]

I have some basic rules in the PREROUTING of *nat that perform a DNAT 
like so:

-A PREROUTING -p tcp --dport 1234 -j DNAT --to 1.2.3.4

However, on a pretty consistent basis this rule fails to be applied and 
I'll see the results of that in the kernel logs like:

Mar 28 15:24:21 hostname IN=eth1 OUT= MAC=<mac addrs> SRC=w.x.y.z 
DST=4.3.2.1 LEN=40 TOS=0x00 PREC=0x00 TTL=242 ID=37514 DF PROTO=TCP 
SPT=3232 DPT=1234 WINDOW=0 RES=0x00 ACK RST URGP=0

The log shows that a small sampling of packets did not apply the DNAT, 
and it is happening enough to notice, I'd say 1 in 100.

Any suggestions on how to troubleshoot and resolve this?

I'm not trying to do anything real fancy, its a simple dual NIC 
interface, eth0 is private and eth1 public.

TIA

--
Ritter