It seems to me, usage of bubba2 server is hardly limited as a router, because it doesn't support
"ip rule ..."
I have two internet network connections (ISPs), and use simple route based load balancing, which requires ip rules (or selection by source address to be more specific) to achieve this.
I'm not fully sure as I can't reliably check kernel configuration, but it seems Kernel doesn't support some of
CONFIG_NETLINK and CONFIG_NETLINK_DEV (or CONFIG_RTNETLINK) options.