Wireless mesh networks may be equipped with multiple Portals that offer access to external networks such as the Internet. These Portals are provided with two interfaces: one to a wired network (to communicate with other Portals and Gateways) and another one to the wireless network. In the current 802.11s standard, the interaction between these two interfaces is not defined. By connecting both interfaces in a seamless way, this paper addresses and solves the problem of dynamically selecting multiple Portals in a Wireless Mesh Network. In particular, the proposal is supported by the definition of an anycast group formed by the Portals in the network. Any data frame whose destination is an external host is routed to any Portal in the network. The route is selected depending on the instantaneous network conditions (e.g. path availability, number of hops, delay or losses). To make this selection a distributed process, a link-layer based forwarding scheme is employed. By means of simulations, we state that the application of the proposed technique yields to significant improvements concerning the network performance.