How to set the default source (src) ip address when you have mulitple IP's on a virtual interface
Solution 1:
In the alias stanza, do not include the gateway. You also don't need the 'network' line at all.
auto eth0
iface eth0 inet static
address x.x.x.209
netmask 255.255.255.0
broadcast x.x.x.255
gateway x.x.x.254
auto eth0:1
iface eth0:1 inet static
address x.x.x.210
netmask 255.255.255.0