I use an Airport Express as primary router - i.e. attached to the modem - and a Time Capsule for back up but also as secondary router in bridge mode to extend the wireless network beyond the reach of the Airport Express.
I am planning to add a NAS to my LAN (via Ethernet to either of the two routers). This requires that I only have one DHCP server - i.e. that the two routers are seen as a single subnet.
Does the configuration above with the Time Capsule in bridge mode result in two DHCP servers or only one (the primary router - Airport Express - whilst the Time Capsule does not act as a DHCP server)?