How do I ensure I'm only using one MAC address with my PublicLAN service?

The simplest method is to connect your router or firewall directly to the CityLink port.

Issues typically arise when a switch is connected between your router/firewall and the CityLink port or when a "Layer 3" switch is used. Most switches support a number of protocols designed for loop prevention, information exchange, and auto configuration. The problem is that these protocols are enabled by default and will result in the switch "chatting" to the CityLink network. These extra packets will often occupy the single allocated MAC and prevent your service from working.

See "Useful Config Statements" below for help preventing a switch from chatting.