The idea
A xen with 4 nics bond in two bondings in mode 1 (backup)
eg. nic1 and nic2 -> bond1
nic3 and nic4 -> bond2

This should work with out a hassle as i see it.

Her comes the tricky part
Is it possible to make a new bond of the bonds in failover mode??
eg bond1 and bond2 -> bond3

for info:
nic1 -> cisco 6500 no1
nic2 -> sw1 -> 6500 no1

nic3 -> cisco 6500 no2
nic4 -> sw1 -> 6500 no2

Paul Thurn - Skulking along since Nw2.15
Never argue with an idiot. They drag you down to their level and beat you with experience.