I have a Linux Server (CentOS) running in my DC, I also have two dedicated internet link. I want to configure failover link for this server as If the link1 goes down the server will be connected with link2 and vice versa.

Please help giving advice and suggestions.

Search in Google for "linux network failover bonding".

Or, if it's Centos 7, search for "teaming".

Hi akmsayeed ,

The following steps are for Centos/Redhat . It's pretty straight forward. In this case I have given my own example for

Step 1
====
Prepare the interface files at /etc/sysconfig/network-scripts/

[root@m132 network-scripts]# cat ifcfg-bond0
DEVICE=bond0
IPADDR=10.0.0.132
GATEWAY=10.0.0.24
NETMASK=255.255.255.0
USERCTL=no
ONBOOT=yes
BOOTPRO=none
BONDING_OPTS="mode=4 miimon=1000"

[root@m132 network-scripts]# cat ifcfg-eth0
DEVICE=eth0
HWADDR=xx.xx.xx.xx.xx.xx
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none

[root@m132 network-scripts]# cat ifcfg-eth1
DEVICE=eth1
HWADDR=xx.xx.xx.xx.xx.xx
USERCTL=no
ONBOOT=yes
MASTER=bond0
SLAVE=yes
BOOTPROTO=none



Step 2
====
add these lines to /etc/modprobe.conf

[root@m132 network-scripts]# cat /etc/modprobe.conf
alias bond0 bonding

Step 3
====
Restart the network service : only on console

#service network restart

then verify your bonding status with

#cat /proc/net/bonding/bond0
#cat /sys/class/net/bond0/bonding/mode
#ifconfig -a ((you should be able to see 3 interface bond0 , eth0 and eth1
#tail -f /var/log/messages OR dmesg

verify by plugging off each interface manually to see if bonding works




Below are the bonding modes
==================

mode=1 (active-backup)
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 (balance-xor)
XOR policy: 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)
Broadcast policy: transmits everything on all slave interfaces. This mode provides fault tolerance.

mode=4 (802.3ad)
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.
Prerequisites:
Ethtool support in the base drivers for retrieving the speed and duplex of each slave.
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 (balance-tlb)
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 (balance-alb)
Adaptive load balancing: includes balance-tlb plus receive load balancing (rlb) 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.
Also you can use multiple bond interface but for that you must load the bonding module as many as you need.


For your case you have to choose the mode you need .... my example was mode 4

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