In one embodiment, a plurality of network interfaces of a network device that are configured to communicate with other network devices in a first computer network are identified as network-to-network interfaces (NNIs). Also, one or more network interfaces of the network device that are configured to provide access to the first computer network to user devices are identified as user-to-network interfaces (UNIs). One or more NNIs of the plurality of NNIs are selected to forward traffic from the network device to an aggregation device of the first network that couples the first computer network to a second computer network. Also, one or more NNIs of the plurality of NNIs that have not been selected to forward traffic from the device to the aggregation device are designated as network-to-network interface alternates (NNI-ALTs). The one or more NNI-ALTs are treated as UNIs for user data traffic forwarding decisions.