[CentOS] CentOS 5.7 Ethernet bonding - order of enslavement matters?

Setting up bonding in active-backup mode 1 (using ARP monitoring)
on a server, it looked OK, but pulling the active link cable
didn't actually work, it didn't fail over.

Eventually with manual playing around with modprobe, ifconfig,
ifenslave, etc., a solution was stumbled upon: enslave the eth1
device before eth0, and all is good.

Why this should matter is a puzzle - I could not find anything in
bonding.txt or on the web about it.

I had to change ifup-eth to fix the problem.

Any ideas on why the enslavement order matters, or a better
solution to work around it?

The rest of this post is details.


To fix this, I had to patch
/etc/sysconfig/network-scripts/ifup-eth to reverse the order when
it is updating the sysfs slaves list.  A 1-line change, from:

for device in $(LANG=C egrep -l "^[[:space:]]*MASTER=\"?${DEVICE}\"?"
/etc/sysconfig/network-scripts/ifcfg-*) ; do

to:

for device in $(LANG=C egrep -l "^[[:space:]]*MASTER=\"?${DEVICE}\"?"
/etc/sysconfig/network-scripts/ifcfg-* | sort -r) ; do


With that change, everything works perfectly.

I don't like this solution (changing standard system files) but
it seems like the best one for now, and should not break
anything.


Maybe it's the particular network devices.  Platform is VIA M850
running CentOS5.7 64-bit, original content from DVD (no yum
update done).

Eth0 is the onboard device, using an updated VIA Velocity driver
(velocityget 1.42 instead of default via-velocity):

05:00.0 Ethernet controller: VIA Technologies, Inc. VT6120/VT6121/VT6122
Gigabit Ethernet Adapter (rev 82)

Eth1 is a Linksys (Cisco) USB300M USB-Ethernet dongle, using asix
driver:

Bus 001 Device 005: ID 0b95:7720 ASIX Electronics Corp. AX88772

Modprobe.conf:

alias eth0 velocityget

With the network service enabled (NetworkManager disabled), this
is my setup:

ifcfg-bond0:

DEVICE=bond0
BOOTPROTO=none
ONBOOT=yes
IPADDR=10.6.0.90
NETMASK=255.255.255.0
GATEWAY=10.6.0.1
BONDING_OPTS="mode=active-backup arp_interval=300 primary=eth0
arp_ip_target=+10.6.0.1 arp_ip_target=+10.6.0.2"

ifcfg-eth0:

DEVICE=eth0
BOOTPROTO=none
ONBOOT=yes
IPADDR=10.6.0.90
NETMASK=255.255.255.0
GATEWAY=10.6.0.1
HWADDR=00:1F:F2:03:FA:45
MASTER=bond0
SLAVE=yes

ifcfg-eth1:

DEVICE=eth1
BOOTPROTO=none
ONBOOT=yes
IPADDR=10.6.1.90
NETMASK=255.255.255.0
GATEWAY=10.6.0.1
MASTER=bond0
SLAVE=yes
HWADDR=58:6d:8f:3d:8d:4f