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Combining the bandwidth of two internet channels and simple failover

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Combining the bandwidth of two internet channels and simple failover

First, let's define the variables: $ cat /etc/balance/vars #!/bin/bash # LAN interface IF0= "eth1" # WAN interface 1 IF1= "eth0" # WAN interface 2 IF2= "ppp0" IP1= "194.9.xx.xx" IP2= "`ip addr show $IF2 | grep inet | awk '{print $2}'`" #…

Combining the bandwidth of two internet channels and simple failover

First, let's define the variables:
$ cat /etc/balance/vars

  1. #!/bin/bash
  3. # LAN interface
  4. IF0="eth1"
  6. # WAN interface 1
  7. IF1="eth0"
  9. # WAN interface 2
  10. IF2="ppp0"
  12. IP1="194.9.xx.xx"
  13. IP2="`ip addr show $IF2 | grep inet | awk '{print $2}'`"
  15. # gateway 1
  16. P1="194.9.xx.xx"
  17. # gateway 2
  18. P2="195.5.xx.xx"
  20. # LAN netmask
  21. P0_NET="192.168.0.0/24"
  22. # WAN1 netmask
  23. P1_NET="194.9.xx.xx/xx"
  24. # WAN2 netmask
  25. P2_NET="195.5.xx.xx/xx"
  28. TBL1="provider1"
  29. TBL2="provider2"
  31. # Relative weight of channels bandwidth
  32. W1="2"
  33. W2="1"


Add two additional routing tables to the /etc/iproute2/rt_tables file:
echo "1 provider1" >> /etc/iproute2/rt_tables
echo "2 provider2" >> /etc/iproute2/rt_tables

Now, let's write a script that will set up all the necessary routes and firewall rules:

cat /etc/balance/routing.sh

  1. #!/bin/bash
  3. . /etc/balance/vars
  5. echo "1" > /proc/sys/net/ipv4/ip_forward
  8. ip route add $P1_NET dev $IF1 src $IP1 table $TBL1 > /dev/null 2>&1
  9. ip route add default via $P1 table $TBL1 > /dev/null 2>&1
  10. ip route add $P2_NET dev $IF2 src $IP2 table $TBL2 > /dev/null 2>&1
  11. ip route add default via $P2 table $TBL2 > /dev/null 2>&1
  13. ip route add $P1_NET dev $IF1 src $IP1 > /dev/null 2>&1
  14. ip route add $P2_NET dev $IF2 src $IP2
  16. ip route add default via $P1 > /dev/null 2>&1
  18. ip rule add from $IP1 table $TBL1 > /dev/null 2>&1
  19. ip rule add from $IP2 table $TBL2 > /dev/null 2>&1
  22. ip route add $P0_NET   dev $IF0 table $TBL1 > /dev/null 2>&1
  23. ip route add $P2_NET   dev $IF2 table $TBL1 > /dev/null 2>&1
  24. ip route add 127.0.0.0/8 dev lo  table $TBL1 > /dev/null 2>&1
  25. ip route add $P0_NET   dev $IF0 table $TBL2 > /dev/null 2>&1
  26. ip route add $P1_NET   dev $IF1 table $TBL2 > /dev/null 2>&1
  27. ip route add 127.0.0.0/8 dev lo  table $TBL2 > /dev/null 2>&1
  29. iptables -t nat -F POSTROUTING
  30. iptables -t nat -A POSTROUTING -s $P0_NET -o $IF1 -j MASQUERADE
  31. iptables -t nat -A POSTROUTING -s $P0_NET -o $IF2 -j MASQUERADE

This set of commands ensures that response packets are routed through the interface on which the request was received, as well as performing masquerading on both interfaces.

Now let's write a script that will determine whether a particular channel is operational and, accordingly, change the default gateway records.

$ cat /etc/balance/check.sh

  1. #!/bin/bash
  3. . /etc/balance/vars
  5. OLDIF1=0
  6. OLDIF2=0
  8. . /etc/balance/routing.sh
  9. while true; do
  12. ping -c 3 -s 100 $P1 -I $IF1 > /dev/null
  13. if [ $? -ne 0 ]; then
  14. echo "Failed IF1!"
  15. NEWIF1=0
  16. else
  17. NEWIF1=1
  18. fi
  20. ping -c 3 -s 100 $P2 -I $IF2 > /dev/null
  21. if [ $? -ne 0 ]; then
  22. echo "Failed IF2!"
  23. NEWIF2=0
  24. else
  25. NEWIF2=1
  26. fi
  28. if (( ($NEWIF1!=$OLDIF1) || ($NEWIF2!=$OLDIF2) )); then
  29. echo "Changing routes"
  31. if (( ($NEWIF1==1) && ($NEWIF2==1) )); then
  32. echo "Both channels"
  33. ip route delete default
  34. ip route add default scope global nexthop via $P1 dev $IF1 weight $W1 \
  35. nexthop via $P2 dev $IF2 weight $W2
  36. elif (( ($NEWIF1==1) && ($NEWIF2==0) )); then
  37. echo "First channel"
  38. ip route delete default
  39. ip route add default via $P1 dev $IF1
  40. elif (( ($NEWIF1==0) && ($NEWIF2==1) )); then
  41. echo "Second channel"
  42. ip route delete default
  43. ip route add default via $P2 dev $IF2
  44. fi
  46. else
  47. echo "Not changed"
  48. fi
  50. OLDIF1=$NEWIF1
  51. OLDIF2=$NEWIF2
  52. sleep 3
  53. done

We check the channel status by pinging the gateway, and if there is no response to 3 consecutive pings, we consider the channel to be down and accordingly exclude it from the routing table.

Thus, if both channels are working:

$ ip route
195.5.xx.xx dev ppp0 proto kernel scope link src 95.133.xx.xx
194.9.xx.xx/xx dev eth0 proto kernel scope link src 194.9.xx.xx
192.168.0.0/24 dev eth1 proto kernel scope link src 192.168.0.75
default
nexthop via 194.9.xx.xx dev eth0 weight 2
nexthop via 195.5.xx.xx dev ppp0 weight 1

In total, we have two default gateways, the first with a weight of 2 and the second with a weight of 1. That is, twice as much traffic will go through the first channel compared to the second.

To customize these scripts for your needs, you need to configure the values in the vars file; the other scripts practically do not require configuration.

Note: This post may be AI-assisted and then human-edited. Editorial responsibility: Dmytro Lomaka, Kaltenkirchen.