Why is bond mode 4 configured in /proc/net/bonding/bond1 when I have configured bond mode 1 in /etc/modprobe.conf on Red Hat Enterprise Linux 5?

Environment

• Red Hat Enterprise Linux 5 (RHEL5)
  • Observed on RHEL5.6 kernel-2.6.18-238.el5, but currently unknown if other versions are also affected.

• 2 or more bonding devices exist (eg. bond0 and bond1)

  • Only minimal bonding information is configured in /etc/sysconfig/network-scripts/ifcfg-bondX:

  $ cat etc/sysconfig/network-scripts/ifcfg-bond1 
  # Intel Corporation 82599EB 10-Gigabit SFI/SFP+ Network Connection
  DEVICE=bond1
  BOOTPROTO=none
  ONBOOT=yes
  USERCTL=no
  IPADDR=172.31.160.33
  NETMASK=255.255.255.240
  

  • The bonding mode is configured via /etc/modprobe.conf:

  $ grep bond etc/modprobe.conf 
  alias bond0 bonding
  options bond0 miimon=100 mode=4               <-- bond0 is configurd mode=4
  alias bond1 bonding
  options bond1 miimon=100 mode=1 primary=eth0  <-- bond1 is configured mode=1