Linux Network Interface Channel Bonding and DHCP

While configuring a few servers I noticed some strange behavior with mode 4 channel bonding (LACP / 802.3ad) and DHCP. You might get the following error message, no matter what you do:

Determining IP information for bond0… failed; no link present. Check cable?

The problem appears to exist in how the interface responds to link status on LACP / 802.3ad ports. The computer is trying to send DHCP packets when the interface itself isn’t ready, causing Linux to think the interface isn’t configured or has no network cable plugged in. This appears to only happen when you use mode 4 channel bonding. Mode 6 works fine. The (band-aid) solution appears to be to trick the system into thinking the interface is already configured. This enables Linux to continue sending DHCP packets until the interface is configured and negotiated successfully with 802.3ad, at which point everything works as planned. Simply insert this at the end of /etc/sysconfig/network-scripts/ifcfg-bond0 – I should note this particular example is for CentOS and RHEL so I haven’t confirmed if this workaround works for Debian based distributions.

check_link_down () { return 1; }