Hi!
- Case & schema:
I want to NAT on Microtic traffic form vlan 1 and pass it through the same cable on vlan 100 as a LAN
Cisco 887 (GW) <----vlan1-----> HP_switch <------vlan1+vlan100-------> port WAN microtic RB2011
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<---------vlan100--------> pozostały LAN
For test I remove HP Switch
I add bridge with vlan100 and vlan 1 interfejs. Bridge was connected to physical WAN port on Microtik as root port. I changed NAT feature on Microtic from physical interfejs to vlan1
interface on Cisco:
interface FastEthernet3
switchport mode trunk
duplex full
speed 100
!
!
interface Vlan1
description default_vlan
ip address 192.168.1.254 255.255.255.0
ip nat inside
ip virtual-reassembly
!
!
YES, i need NAT twice 
- Observation::
vlan1 - don’t receive IP from Cisco (when I operate on physical interface everything works properly). Cisco router has SVI, not subinterfaces.