iptables NAT forwarding adding 75-100ms

[Mike Lovell]

I have a strange occurrence of lag on my local networking. I have a
cable modem that plugs into a Debian server, then that Debian server is
plugged into a switch that all other machines in the house connect to.

So something like:

wan0 -> wan
eth0 -> lan

The relevant forwarding/NAT rules are:


#iptables -A FORWARD -i wan0 -o eth0 -m state --state RELATED,ESTABLISHED -j ACCEPT
#iptables -A FORWARD -i eth0 -o wan0 -j ACCEPT

#iptables -t nat -A POSTROUTING -o wan0 -j MASQUERADE


So pretty standard boring NAT.

Lag is occurring (between 75ms and 100ms) on all forwarding rules. Apart
from the lag they function fine (no connectivity issues).


Ping: LAN Machine -> Debian Router = ~0.7ms
Ping: Debian Router -> Google = ~20ms
Ping: LAN Machine -> Google = ~121ms !!!


The Debian server has plenty of free RAM, the load is showing as low,
it's (at this time) entirely dedicated to routing - Why is it
introducing 100ms of lag into forwarded traffic???

Anyone else seen similar to this???


I get great speed from LAN machines, just high latency.

~ Mike