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Simple Linux Load Balancing with `iproute2`
#!/bin/bash
# Load balance multiple internet connections. Requires iproute2, awk and grep.
# (C) 2016 Tobias Girstmair, isticktoit.net, GPLv2
# Also useful: speedometer -l -r eth1 -t eth1 -m $(( 1024 * 1024 * 3 / 2 ))
# Not much user error checking is done - only pass working network connections
# script needs root to work and at least two interfaces to be useful
[ $EUID -eq 0 -a $# -ge 2 ] || {
echo "Usage (as root): $0 iface1[:weight1] iface2[:weight2] ..." >&2
exit 1
}
get_free_tblnum() { # http://stackoverflow.com/a/28702075
awk -v RS='\\s+' '{ a[$1] } END { for(i = 10; i in a; ++i); print i }'</etc/iproute2/rt_tables
}
loadbal() {
IFS=':' read IFACE WEIGHT <<< "$1"
TABLE="${IFACE}loadbalance"
if ! grep -q -w "$TABLE" /etc/iproute2/rt_tables ; then
echo "$(get_free_tblnum) $TABLE" >> /etc/iproute2/rt_tables
fi
MY_IP=$(ip -o -4 addr show $IFACE |awk -F'(\\s|/)+' '{print $4}')
GW_IP=$(ip route show dev $IFACE | awk '/default/ {print $3}')
SUBNT=$(ip route show dev $IFACE | awk '/proto kernel/ {print $1}')
ip route add $SUBNT dev $IFACE src $MY_IP table $TABLE
ip route add default via $GW_IP table $TABLE
ip rule add from $MY_IP table $TABLE
echo nexthop via $GW_IP dev $IFACE weight ${WEIGHT:-1}
}
ip route add default scope global $(for IF in "$@"; do loadbal $IF; done)
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