When a bonding device releases a slave, a warning message is printed, similar to: "bonding: bond0: Warning: the permanent HWaddr of eth0 - xx:xx:xx:xx:xx:xx - is still in use by bond0"

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 5

Issue

  • On an active bond, you may see the following warning message:
         # service network restart
         bonding: bond0: Warning: the permanent HWaddr of eth0 - 00:26:B9:xx:xx:xx - is still in use by bond0. Set the HWaddr of eth0 to a different address to avoid conflicts.
  • The service network restart command is a simple way to trigger this, basically any time a slave is released while the bond is still up, this warning will be printed.

Resolution

  • This is only a warning message, no further action is required. The rest of this document is only provided for the purpose of explaining the details behind this warning message, but the steps described below are usually not required.

Root Cause

  • In general, bonding will, by default, use the mac address of the first slave it enslaves (there are exceptions, it depends on the bonding mode). This initial mac address is used, by default, at least until the bonding interface is next "restarted" (except when using balance-tlb, or balance-alb mode, or active-backup mode with fail_over_mac option, set to something else but the default of "none or 0"). Here's an example:
# ifconfig | grep HWaddr
bond0     Link encap:Ethernet  HWaddr 54:52:00:AA:AA:AA
eth0      Link encap:Ethernet  HWaddr 54:52:00:AA:AA:AA
eth1      Link encap:Ethernet  HWaddr 54:52:00:AA:AA:AA

- The slaves and the bond interface share the same one mac address while the bond interface is controlling the slaves, this is normal, default and intended behavior.

# ifdown eth0
bonding: bond0: Warning: the permanent HWaddr of eth0 - 54:52:00:AA:AA:AA - is still in use by bond0. Set the HWaddr of eth0 to a different address to avoid conflicts.

  • eth0's original MAC address is 54:52:00:AA:AA:AA. If eth0 is released from the bonding master, the sysadmin might chose to configure this interface as a stand alone interface, this would cause a duplicate mac address on the same network segment, the warning message is designed to avoid that by notifying the sysadmin of this danger before it happens. Please note: if there is no intention to reuse this released slave immediately as a standalone interface, no further action is needed. This is normal behavior, it is perfectly safe and there is nothing to worry about.

  • If the intention is to permanently release eth0, the former slave of bond0 (in this example), and us it on it's own, simply follow these steps:

    • edit ifcfg-eth0, remove the "SLAVE=yes" and "MASTER=bond0" statements, and add the needed configuration required for eth0 (ip address, netmask/prefix, etc)
    • (optional) configure another interface as a slave of bond0, to replace eth0
    • service network restart

  • At this point, bond0 will be using the mac address of one of it's currently configured slaves (not eth0), and the mac address of eth0 will no longer be used. eth0 can now be used on it's own, safely. (to verify this, just do "ifconfig -a" or "ip link show" and verify that eth0's mac address is unique in that output)

  • The following is another possibility, note that it is not necessary or recommended to do this:

  • This message can be avoided by specifying a MAC address for bond0 . To do this, add the following line to #/etc/sysconfig/network-scripts/ifcfg-bond0

MACADDR=YY:YY:YY:YY:YY:YY

  • Each "YY" is an octet of the mac address, expressed as a hexadecimal number. This MAC address must be unique within the same segment.

  • hexadecimal is "0 to 9 and A to F" (or in short: 0 - F)

Diagnostic Steps

  • This is a warning message, no action is required based on this message alone. For further details, please see the discussion under "Root Cause".

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