Using lagg(4) with diskless booting

The lagg interface enables transparent failover between (eg) wired & wifi interfaces - making it trivial to combine the flexibility of walking around the house without any cables with the throughput of a wired interface by simply connecting and disconnecting the LAN cable.

For a normal boot environment, this is as simple as placing something like the following in /etc/rc.conf:

ifconfig_re0="up"
ifconfig_ath0="ether 00:1e:68:aa:bb:cc"  # Set WiFi MAC address to match wired MAC address
wlans_ath0="wlan0"
ifconfig_wlan0="WPA"
cloned_interfaces="lagg0"
ifconfig_lagg0="SYNCDHCP laggproto failover laggport re0 laggport wlan0"

If you have multiple boxes available, supporting diskless booting provides a convenient way to install, upgrade or recover systems. It can also provide a convenient way to test a planned upgrade without installing the upgrade onto the target host. One downside of diskless booting is that the root filesystem is NFS mounted via the boot interface and it's not possible to PXE boot from a WiFi or lagg interface. Whilst you would typically want the performance of a wired interface for installing/upgrading/recovering, lagg support is important for regression testing and can make installing/upgrading/recovering more convenient. Following some experimentation, I came up with the following configuration:

host client_host { # Client name

  hardware ethernet 00:1e:68:aa:bb:cc;           # Wired NIC MAC address
  fixed-address client.f.q.d.n;                  # FQDN of diskless client
  filename "/tftpboot/pxeboot";
  next-server 10.11.12.13;                       # Boot/root server IP
  vendor-option-space FreeBSD;
  option root-path "10.11.12.13:/client/root";   # NFS path to client root filesystem
  option host-name "client.f.q.d.n";
}

ifconfig_ath0="ether 00:1e:68:aa:bb:cc"  # Set WiFi MAC address to match wired MAC address
wlans_ath0="wlan0"
ifconfig_wlan0="WPA"
cloned_interfaces="lagg0"
ifconfig_lagg0="laggport wlan0"