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| to be run periodically (I do it every minutes for a 3 ISP setup)
| | I run it on alpine 3.13: https://github.com/jchdel/select-fastest-gateway |
| <pre>
| |
| #!/bin/bash
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| # This script configure the router to use fastest available gateway
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| # as default one. It uses some bashism...
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| [ -f /tmp/router.order ] && logger "Already running" && exit 1
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| NICS=($(ip -br link|awk '{print $1}')) # index 0 is loopback (lo)
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| NNICS=$((${#NICS[@]}-1))
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| GWS=()
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| IPS=()
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| iptables -t mangle -F
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| iptables -t nat -F
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| # Did we lost all of our gateways?
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| ip route | grep -q default || \
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| for ((i=1; i<=$NNICS; i++))
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| do
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| ifdown ${NICS[$i]}
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| ifup ${NICS[$i]} && \
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| logger "${NICS[$i]} restarted." || \
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| logger "Unable to restart ${NICS[$i]}."
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| done
| |
| # Prepare routing tables for each gateway
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| for ((i=1; i<=$NNICS; i++))
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| do
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| IPS[$i]="$(ip a s ${NICS[$i]}|awk '/inet/{print $2}'|cut -d/ -f1)"
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| [ -z "${IPS[$i]}" ] && GWS[$i]="" && continue
| |
| # disable kernel filtering of "unwanted" packets
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| echo 0 > /proc/sys/net/ipv4/conf/${NICS[$i]}/rp_filter
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| GWS[$i]="$(ip r | grep default | grep -v dead | grep ${NICS[$i]} | cut -d\ -f3)"
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| [ -z "${GWS[$i]}" ] && continue
| |
| # duplicate main routing table for each live default gateway
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| ip route flush table $i
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| ip route show table main | grep -Ev ^default | while read ROUTE ; do
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| ip route add table $i $ROUTE
| |
| done
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| # add default gateway
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| ip route add table $i default via ${GWS[$i]} dev ${NICS[$i]}
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| # mark packets from localhost
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| iptables -t mangle -A OUTPUT -s ${IPS[$i]} -j MARK --set-mark $i
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| # activate alternate routing
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| while $(ip rule del fwmark $i table $i);do .;done 2>/dev/null
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| ip rule add fwmark $i table $i prio ${i}0
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| # MASQUERADE or SNAT ?
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| iptables -t nat -I POSTROUTING -o ${NICS[$i]} -j MASQUERADE #SNAT --to-source ${IPS[$i]}
| |
| done
| |
| # activate changes in policy routing
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| ip route flush cache
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| # ping same target via each gateway
| |
| for ((i=1; i<=$NNICS; i++))
| |
| do
| |
| [ -z "${GWS[$i]}" ] && continue
| |
| ( ping -n -c 5 -q -I ${IPS[$i]} 1.1 >/dev/null \
| |
| && logger "1.1 responded for ${IPS[$i]} dev ${NICS[$i]}" \
| |
| || logger "No response from 1.1 for ${IPS[$i]} dev ${NICS[$i]}" ; \
| |
| echo $i >> /tmp/router.order ) &
| |
| done
| |
| wait -n # first gateway to complete
| |
| # meanwhile, main routing table is still active
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| INDEX=$(head -1 /tmp/router.order)
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| METRIC=1
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| for ((i=1; i<=$NNICS; i++))
| |
| do
| |
| [ -z "${GWS[$i]}" ] && continue
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| ip route del default via ${GWS[$i]} dev ${NICS[$i]}
| |
| done
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| ip route add default via ${GWS[$INDEX]} dev ${NICS[$INDEX]} metric $METRIC
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| echo 1 > /proc/sys/net/ipv4/ip_forward
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| logger "Default route set via ${GWS[$INDEX]} dev ${NICS[$INDEX]}."
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| wait # other gateways
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| cat /tmp/router.order | while read i
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| do
| |
| [ $i -eq $INDEX ] && continue
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| METRIC=$(($METRIC+1))
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| ip r a default via ${GWS[$i]} dev ${NICS[$i]} metric $METRIC
| |
| done
| |
| rm -f /tmp/router.order
| |
| exit 0
| |
| </pre>
| |