When you are running bonding in active-backup mode, you can detect which slave is active by listing /proc/net/bonding/bond0. How to change active slave?
[root@rs01 ~]# cat /proc/net/bonding/bond0 Ethernet Channel Bonding Driver: v3.4.0 (October 7, 2008) Bonding Mode: fault-tolerance (active-backup) Primary Slave: None Currently Active Slave: eth1 MII Status: up MII Polling Interval (ms): 0 Up Delay (ms): 0 Down Delay (ms): 0 ARP Polling Interval (ms): 250 ARP IP target/s (n.n.n.n form): 10.0.0.1, 10.0.0.2, 10.0.0.3, 10.0.0.200 Slave Interface: eth1 MII Status: up Link Failure Count: 2 Permanent HW addr: 00:1b:21:46:64:42 Slave Interface: eth0 MII Status: up Link Failure Count: 2 Permanent HW addr: 00:24:81:26:c1:43
To switch to other slave, just remove active interface from bonding configuration
echo -eth1 > /sys/class/net/bond0/bonding/slaves
Bonding will continue with other interface, which becomes active. Now you can put interface eth1 back to bonding
echo +eth1 > /sys/class/net/bond0/bonding/slaves