Network Failover Howto

[tcpip4lyfe]

So you have 2 network adapters in your server and you want to configure one of them to fail over if your connection on the other goes down. It's pretty easy:

sudo pico /etc/modules

##add this at the bottom
bonding mode=active-backup miimon=100

Save and exit

sudo apt-get install ifenslave-2.6

Edit your /etc/network/interfaces

sudo pico /etc/network/interfaces

###Adapter bonding for Eth0 and Eth1
auto bond0
iface bond0 inet static
address 10.0.0.104
netmask 255.255.0.0
gateway 10.0.0.1
post-up ifenslave bond0 eth0 eth1
pre-down ifenslave -d bond0 eth0 eth1


And that's it!

Reboot and test.


The nitty gritty:


There are several different modes of bonding that can be configured:
Taken from: http://howtoforge.com/network_bonding_ubuntu_6.10

mode=0

This mode uses the Round-robin policy: Transmit packets in sequential order from the first available slave through the last. This mode provides load balancing and fault tolerance. (this is the mode we just setup)

mode=1

This mode uses an Active-backup policy: Only one slave in the bond is active. A different slave becomes active if, and only if, the active slave fails. The bond's MAC address is externally visible on only one port (network adapter) to avoid confusing the switch. This mode provides fault tolerance. The primary option affects the behavior of this mode.

mode=2

Transmit based on [(source MAC address XOR'd with destination MAC address) modulo slave count]. This selects the same slave for each destination MAC address. This mode provides load balancing and fault tolerance.

mode=3

Broadcast policy: transmits everything on all slave interfaces. This mode provides fault tolerance.

mode=4

IEEE 802.3ad Dynamic link aggregation. Creates aggregation groups that share the same speed and duplex settings. Utilizes all slaves in the active aggregator according to the 802.3ad specification.

*Pre-requisites:

1. Ethtool support in the base drivers for retrieving the speed and duplex of each slave.

2. A switch that supports IEEE 802.3ad Dynamic link aggregation. Most switches will require some type of configuration to enable 802.3ad mode

mode=5

Adaptive transmit load balancing: channel bonding that does not require any special switch support. The outgoing traffic is distributed according to the current load (computed relative to the speed) on each slave. Incoming traffic is received by the current slave. If the receiving slave fails, another slave takes over the MAC address of the failed receiving slave.

*Prerequisite: Ethtool support in the base drivers for retrieving the speed of each slave.

mode=6

Adaptive load balancing: includes balance-transmit load balancing plus receive load balancing for IPV4 traffic, and does not require any special switch support. The receive load balancing is achieved by ARP negotiation. The bonding driver intercepts the ARP Replies sent by the local system on their way out and overwrites the source hardware address with the unique hardware address of one of the slaves in the bond such that different peers use different hardware addresses for the server.