Script to to do UDP load balancing using NetFilter

iptables_lb_8125.sh

#!/bin/bash

# enable forwarding
echo 1 >| /proc/sys/net/ipv4/ip_forward

# get softirq sharing between CPU cores for Receive Packet Steering
# https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Performance_Tuning_Guide/network-rps.html
for rxq in $(ls -1 /sys/class/net/*/queues/rx-*/rps_cpus)
do
  echo $(taskset -p 1 | cut -d':' -f2 | tr -d '[:space:]') >| $rxq
done

# clear rules
iptables -t filter -F
iptables -t filter -X
iptables -t nat -F
iptables -t nat -X
iptables -t mangle -F
iptables -t mangle -X
iptables -t filter -P INPUT ACCEPT
iptables -t filter -P OUTPUT ACCEPT
iptables -t filter -P FORWARD ACCEPT

# dnats
iptables -t nat -N DNAT8126
iptables -t nat -A DNAT8126 -p udp --dport 8125 -j REDIRECT --to-port 8126

iptables -t nat -N DNAT8127
iptables -t nat -A DNAT8127 -p udp --dport 8125 -j REDIRECT --to-port 8127

# round robin balance DNAT requests
iptables -t nat -N ROUNDROBIN
iptables -t nat -A ROUNDROBIN -m statistic --mode nth --every 2 --packet 0 -j DNAT8126
iptables -t nat -A ROUNDROBIN -m statistic --mode nth --every 2 --packet 1 -j DNAT8127

# despatch NEW connections to the round-robin chain
iptables -t nat -A PREROUTING -p udp --dport 8125 -j ROUNDROBIN