Floodless in SEATTLE

This paper proposes an architecture for managing Ethernet routing over an enterprise-type network. It aims to provide more scalability than Ethernet bridging and easier administration and address portability than IP subnetting and VLAN-based approaches. In this approach, switches use a link-state protocol to route amongst themselves, and, using this, form a DHT to store end-host routing information. This DHT distributes the routing information across the routers so the amount of information stored by each switch is proportional the average number of end hosts a router has. This information is, of course, not local to the switches which need it, so switches maintain a cache of this information, invalidated (by the destination switch) on the use of a stale entry. To interact with unmodified end hosts, the authors implement ARP and DHCP backed by information in the DHT. ARP broadcasts used to invalidate cached are translated to unicasts to interested hosts by tracking which hosts may have cached entries.

The authors evaluated their using a trace driven simulation on several real network topologies and an evaluation with an actual implementation on a very small network.
From the simulations, they showed that the information maintained per router was actually smaller than both Ethernet bridging based approaches and that it achieved better routes (given similar cache sizes) than past identity-based routing proposals. From the actual implementation, they measured the per-packet overhead, performance when attempting to contact many non-existent hosts, and switch fail-over speed.

It's unfortunate that this paper did not include an explicit comparison to IP subnetting or VLANs, by which it is clearly motivated. It is understandable why, of course; their arguments against IP subnetting are based on ease of configuration which is very difficult to measure. For VLANs, only some of their complaints were about ease of configuration, but for the others it might be hard to infer a suitable configuration from their topology information.

This scheme is attractive for its careful attention to complete transparency for end-hosts, which should make it relatively easy to deploy. The big problem is that deploying it in the most straightforward way involves changing all switches over; it would seem, however, that there's probably some way of constructing a reasonable middle-ground where it is deployed gradually across the network.