Linux Samba/Domain computer with two physical nics connected to two completely different physical networks.
I'm attempting to multihome this Samba/Domain controller server.

NIC em1 network settings.
IP: 172.16.20.39
mask: 255.255.255.0

gateway: 172.16.20.1

NIC em2 network settings.
IP: 172.16.128.39
mask: 255.255.255.0
I added an additional route like so.. 
add -net 172.16.128.0 netmask 255.255.128.0 gw 172.16.128.1 dev em2

Everything seems fine, a Windows systems on the x.x.128.x can mount a share from this Domain controller but they are unable to login to this domain.  No domain services available.
Is it my route?