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I am trying to set up fail-back configuration in bonding but I am unable to get around the interface configuration. My interface is as follow:

auto bond0

iface bond0 inet static

       address 192.168.1.39

       netmask 255.255.255.0

       up /sbin/ifenslave bond0 eth1 eth3

       down /sbin/ifenslave -d bond0 eth1 eth3

My /etc/modprobe.d/bonding.conf file is:

alias bond0 bonding

options bonding mode=3

I test it by running ping from other system. My bond status is as follows:

Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: fault-tolerance (broadcast)

MII Status: up

MII Polling Interval (ms): 0

Up Delay (ms): 0

Down Delay (ms): 0



Slave Interface: eth1

MII Status: up

Speed: 1000 Mbps

Duplex: full

Link Failure Count: 0

Permanent HW addr: 44:a8:42:03:68:2c

Slave queue ID: 0



Slave Interface: eth3

MII Status: up

Speed: 1000 Mbps

Duplex: full

Link Failure Count: 0

Permanent HW addr: 44:a8:42:03:68:2c

Slave queue ID: 0

When I remove eth1 cable the fail-over works and eth3 carries out the data (The ping still continues).

If I connect back eth1 and remove eth3 the ping stops and the bonding status doesn't contain any of the interface. The bond status is:

Ethernet Channel Bonding Driver: v3.7.1 (April 27, 2011)

Bonding Mode: fault-tolerance (broadcast)

MII Status: up

MII Polling Interval (ms): 0

Up Delay (ms): 0

Down Delay (ms): 0

I tried with all the modes in the bonding ( 0 to 6 ). But none of the configuration provides the fail-back support. Where am I going wrong?

EDIT 2019-01-10: These instructions are for Ubuntu 16.04 and older. I will try to update with instructions for 18.04.

In this answer, we are using active-backup bonding with a bond-primary interface set that allows for fail-over to go back to the primary when it is available. More information can be found: https://wiki.linuxfoundation.org/networking/bonding

Bonding in Ubuntu is a different setup then as in other distros of Linux like RedHat. I have done a few bonding configurations in Ubuntu and I will lay it out below as best as possible.

As it looks, you already have ifenslave installed, but if not, install ifenslave:

sudo apt-get install ifenslave

Next, take a look at /etc/modules and make sure it has the following lines:

loop

lp

rtc

bonding

In the /etc/network/interfaces file, set your loopback, eth1, and eth3 interfaces:

auto lo

    iface lo inet loopback



auto eth1

    iface eth1 inet manual

    bond-master bond0

    bond-primary eth1



auto eth3

    iface eth3 inet manual

    bond-master bond0

Now set your bond0 interface with active-backup for fail-over if one of the NIC connections fail:

auto bond0

    iface bond0 inet static

    address 192.168.1.39

    netmask 255.255.255.0

    network 192.168.1.0

    broadcast 192.168.1.255

    gateway 192.168.1.1

    bond-mode active-backup

    bond-miimon 100

    bond-slaves none

Save the changes to /etc/network/interfaces file and restart your networking service:

sudo /etc/init.d/networking restart

Now you can check your bonding setup. Make sure that your bond0, eth1 and eth3 are correct:

sudo ethtool bond0

sudo ethtool eth1

sudo ethtool eth3

Check to see if fail-over now works by removing eth1 from bond0:

sudo ifenslave -d bond0 eth1

Check to see if you can still ping the gateway:

ping -c2 192.168.1.1

Add eth1 back to bond0:

sudo ifenslave bond0 eth1

Hope this helps!