Why does /proc/net/bond0/bonding show that the network interface card's link is up when the cable is unplugged within a bonding environment?

Solution Verified - Updated

Environment

Red Hat Enterprise Linux 5

Issue

When a network interface card cable is unplugged, the link should become "down" in /proc/net/bond0/bonding. Sometimes, unfortunately, the link still shows up even though the cable is unplugged.

Resolution

The bonding parameter use_carrier can be used to solve this problem. This parameter is used to specify the method of determining the link status: MII/ETHTOOL ioctls or netif_carrier_ok(). The default method is to use netif_carrier_ok(). If bonding insists that the link is up when it should not be, it may be that your network device driver does not support netif_carrier_on/off. In this case, setting use_carrier to 0 will cause bonding to revert to using the MII/ETHTOOL ioctl method to determine the link state.

For example:

     # cat /etc/modprobe.conf 
     alias bond0 bonding 
     options bonding mode=1 miimon=100

Add the use_carrier parameter to the options line:

     # cat /etc/modprobe.conf 
     alias bond0 bonding 
     options bonding mode=1 miimon=100 use_carrier=0
Comments

For further information, refer to /usr/share/doc/kernel-doc-*/Documentation/networking/bonding.txt.

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