These are needed to support vxlan encapsulation. In a vxlan packet,
the only place we can straightforwardly hold the source and
destination peers identifiers used by the weave router is in the
24-bit VNI (vxlan network identifier) field. This gives us 12 bits to
indicate a peer. The resulting limit of 4096 peers on a weave network
does not seem like a problem in the near future. But it does mean
that decentralized allocation makes collisions fairly likely even in
weave networks of sizes that are common today. Fortunately, the
problem is much more tractable than IPAM because we can detect when
collisions occur and take action to resolve them.
TODO: We already notify the InterHost when a short id -> peer mapping
changes, but we also need to flush any entries in the router MAC cache
that might be affected.
David Wragg