gretap tunnel redirecting 2 different networks on destination host to nics

How can I get the 10.11.12.x traffic received on tun1 at host B to eth2, 
and traffic 172.16.1.x to eth1? 

When I put the tun1 interface of server B in a bridge with eth1 I am 
able to ping several 172.16.1.x ip's from server A. And communication on 
this network seems to be ok.

When I add eth2 to the bridge, the whole network goes down. (Because of 
a 'loop'?)
I thought of creating a 2nd gretab tunnel and use each tunnel for a 
network, but I think there is probably a better solution. I also don’t 
think iptables should be necessary, because I don’t want to do any 
natting (However I have default policy DROP on INPUT, OUTPUT, FORWARD)


I have a server A that sends 172.16.1.x and 10.11.12.x traffic via a 
gretab tunnel 192.168.1.x to server B. (Putting vms with a macvtap on 
tun1 on host A)

            +-------------+                             +------------+
 172.16.1.x |      B      |                             |      A     |
     -------|eth1         |         192.168.1.x GRETAP  |            |
            |         tun1|-----------------------------|tun1        |
 10.11.12.x |             |                             |            |
     -------|eth2         |                             |            |
            +-------------+                             +------------+