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I have a raspberry pi with three interfaces connected, eth0, wlan0 and ppp0, what i'm looking to achieve is having routes to the internet through all interfaces, but so far only eth0 and ppp0 gets a route.

here's outputs of route -n and ip route show (don't have a working ppp0 interface now but i know that one works)

Kernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 0.0.0.0 192.168.1.1 0.0.0.0 UG 0 0 0 eth0 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 wlan0 default via 192.168.1.1 dev eth0 192.168.1.0/24 dev eth0 proto kernel scope link src 192.168.1.39 192.168.1.0/24 dev wlan0 proto kernel scope link src 192.168.1.243

I wrote a script that is triggered from /etc/dhcp/dhclient-exit-hooks.d/ so once the interface gets an offer from dhcp.

#!/bin/bash calculateCIDR() { nbits=0 IFS=. for dec in $1 ; do case $dec in 255) let nbits+=8;; 254) let nbits+=7;; 252) let nbits+=6;; 248) let nbits+=5;; 240) let nbits+=4;; 224) let nbits+=3;; 192) let nbits+=2;; 128) let nbits+=1;; 0);; *) echo "Error calulating CIDR exiting."; exit 1 ;; esac done echo $nbits } calculateSubnet() { IFS=. read -r i1 i2 i3 i4 <<< $1 IFS=. read -r m1 m2 m3 m4 <<< $2 echo "$((i1 & m1)).$((i2 & m2)).$((i3 & m3)).$((i4 & m4))" } # check if all parameters are there # expected parameters # $1 = iface # $2 = ip # $3 = mask # $4 = gateway if [ $# -ne 4 ] then echo "Illegal number of arguments" exit 2 fi # assign variables IFACE=$1 IP=$2 MASK=$3 GATEWAY=$4 # extract inface number and calculate table number case $IFACE in eth*) TABLEID=$(( 10 + `echo $IFACE | grep -o -E '[0-9]+'`)) METRIC=0 ;; wlan*) TABLEID=$(( 30 + `echo $IFACE | grep -o -E '[0-9]+'`)) METRIC=$(( 50 + `echo $IFACE | grep -o -E '[0-9]+'`)) ;; ppp*) TABLEID=$(( 90 + `echo $IFACE | grep -o -E '[0-9]+'`)) METRIC=$(( 100 + `echo $IFACE | grep -o -E '[0-9]+'`)) ;; *) echo "Bad interface exiting" exit 1 ;; esac # create new table for interface only if not existing there already grep -q -F "$TABLEID $IFACE" /etc/iproute2/rt_tables || echo "$TABLEID $IFACE" >> /etc/iproute2/rt_tables # remove previous rules while ip rule delete table $IFACE 2>/dev/null; do true; done # flush previous table ip route flush table $IFACE # calculate CIDR from CIDR=$(calculateCIDR $MASK) # calculate subnet address SUBNET=$(calculateSubnet $IP $MASK) # create route for local network ip route add $SUBNET/$CIDR dev $IFACE src $IP metric $METRIC table $IFACE # create route for internet ip route add default via $GATEWAY dev $IFACE metric $METRIC table $IFACE # set rules for the interface ip rule add from $IP/32 table $IFACE ip rule add to $IP/32 table $IFACE # done exit 0

this same script is used for all interfaces provided with network setup, wlan0 never gets a route to internet meaning i can't use it to ping anything outside the local network. anyone knows why ? i'm running out of ideas.

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    In general, you can't. Multiple routes to the same destination for load balancing via different interfaces don't work. Bonding only works if both sides bond. The best you can do is to use some kind of fallback mechanism (e.g., use WLAN if the LAN goes down). Commented Mar 1, 2018 at 13:01
  • Bond 1 works with quick mac address expiration of the inactive member so, there is no need that both network equipments implement it. Stop spreading missinformation. Take a look at my comment at my answer and official documentation - kernel.org/doc/Documentation/networking/bonding.txt - Bond does not require LACP Commented Mar 1, 2018 at 17:57
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    Look at this (outdated) documentation about having multiple links to internet: lartc.org/howto/lartc.rpdb.multiple-links.html . Parts 4.2 and 4.2.1 are mostly fine, part 4.2.2 doesn't work anymore (but using iptables' statistic --mode nth + MARK along with ip rule's fwmark does work). Anyway the solution proposed does indeed use this kind of setting: using additional routing tables Commented Mar 4, 2018 at 15:53

1 Answer 1

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First: Always use ip(8) command instead. route is one of those Linux commands on it's way to deprecation. Basically, Linux route was ported from other OS and does not work with Linux routing table scheme(it only shows main table).

main route table is always implicit. Before matching what needs to be routed through main, table local is also looked by the Kernel(basically all broadcast, local address and loopback is there). That's why you can't have a default route on each interface, cause when routing on table main only one of the default will have precedence over others. Look what tables you have with ip rule list.

What you will have to do to configure basic redundancy is:

  • Create 2 rules(say, link01 and `link02) and its routing tables
  • Keep default route empty on main table.
  • Create one default route to table link01 and other to link02.
  • Create rules to those tables or iptables rules when you will match each table
  • Create separated network ip ranges to Wifi and Cable connections.

You face a problem on your current setup: You are repeating a default route on the same gateway and on the same table(main) to different interfaces(probably facing the "route already exists" error when trying to add the default route the second time). This is never going to happen. How arp is supposed to deal with the same IP being published on 2 interfaces at the same time?

Alternative solution:

If you want some redundancy like an active-backup solution without having to change the items i've enlisted above, you could use a bonding interface configured on mode 1, put eth0 and wlan0 as slaves. This is a Debian example of /etc/network/interfaces so you will have to adapt to your distribution: 

# Slaves auto eth0 iface eth0 inet manual bond-master bond0 bond-primary eth0 bond-mode active-backup auto wlan0 iface wlan0 inet manual wpa-conf /etc/network/wpa.conf bond-master bond0 bond-primary eth0 bond-mode active-backup # Master auto bond0 iface bond0 inet dhcp bond-slaves none bond-primary eth0 bond-mode active-backup bond-miimon 100

This way you will connect on cable and wifi, and have an "unified" ip address to both.

If you have a mid/high end network switch that is able to do LACP(IEEE 802.3ad) you can do a link aggregation that will use both cables/connections at the same time(and bond mode of Linux will be 4).

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  • Note that bonding interfaces only works if the communication partner (e.g. the home router) also bonds the interfaces in the same way. In particular, this setup will force all other clients to be both on LAN and WLAN, and have configured it the same way. Commented Mar 1, 2018 at 12:59
  • Your statement is not completly right. If you use LACP(bond mode 4) yes, you will need a network asset that is IEEE 802.3ad readly, a protocol that is comonly known as "port-channel" on Dell and Cisco Switches. If you use bond mode 1, there is no need of a special protocol to negotiate link failover. Bond 1 will deal with Mac changes - wiki.centos.org/TipsAndTricks/BondingInterfaces - I'm also assuming here based on the IP addressing used by OP, that he/she has a AccessPoint that uses the same network(192.168.0.0/24) to both wired and wireless, making this setup with bond 1 possible Commented Mar 1, 2018 at 17:44
  • Bond 1 (failover mode) will only use one network adapter, or in other words, "the best you can do is to use some kind of fallback mechanism", as I said in the comment above. It's not the same as "having routing to the internet with multiple interfaces". Commented Mar 1, 2018 at 17:55
  • I gave one OPTION to one who is asking that will not require changing ip address to wireless neither messing with ip rules, ip route tables an iptables, the same way it seems that he/she is using an home router and not an equipment that is prepared for dealing with LACP... Commented Mar 1, 2018 at 17:59
  • Sometimes if you keep the default route empty, there's nothing allowing a packet to reach the correct iptables entry that will alter this default route. It's still best to have a default route (even a never working route), even if it will be overriden with some rules, just to have those rule be actually working Commented Mar 4, 2018 at 15:56

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