One bridge. See http://forum.mikrotik.com/t/using-routeros-to-vlan-your-network/126489/1 http://forum.mikrotik.com/t/routeros-bridge-mysteries-explained/147832/1 https://help.mikrotik.com/docs/display/ROS/Switch+Chip+Features#SwitchChipFeatures-SetupExamples for RouterOS, https://help.mikrotik.com/docs/pages/viewpage.action?pageId=76415036#CRS3xxandCSS32624G2S+seriesManual-VLANConfigurationExample for SwOS.
The bridge and VLANs segregate the layer 2 / ethernet networks, by default layer 3 / IP packets are forwarded between networks unless you have firewall rules to restrict them.