Hierarchical MAC address space in public Ethernet networks

Service providers are showing strong interest in building all-Ethernet public metropolitan networks that would compete with (and eventually replace) the existing network infrastructures based on SONET, Frame Relay, ATM and similar technologies. The main driving factor is the cost, as Ethernet-based technology is typically cheaper than any others available on the market. Despite successful initial laboratory and field deployment tests, there are still many unresolved issues related to metropolitan-scale Ethernet, such as the appropriateness of a spanning tree algorithm, broadcast flooding and MAC address table explosion in core switches. This paper focuses on the problem of MAC address table explosion by introducing a hierarchy into the address space, through Ethernet-inside-Ethernet packet encapsulation. The encapsulation allows core switches to be standard Ethernet switches, while the edge switches implement concepts presented in this paper. The proposed concept is thus transparent to the existing infrastructure and thereby allows building the network using readily available low-cost layer-2 switches.