Why not just use IP multicast and limit it to just the UDP port numbers needed for this application?
Last I checked, which was some years ago, there was no well-maintained multicast routing daemon for linux. Matt did some research last night and it seems like mrouted is actively maintained for linux now. There is no package in current openwrt though. I will try to do some experiments with mrouted to see if it does what we need and if so we can roll it into our firmware.
Me and cel talked about what would need to be done last night and assuming mrouted works for us, that should be enough for ssb nodes to discover each-other across the mesh. However, it would then be nice if ssb used mDNS and DNS-SD instead of its current ad-hoc multicast discovery implementation. There is a nice node module for this written by mafintosh and it would mean that we can revive the people's open network service browser as well, which is a web app we started working on a while back to list all active services running on the mesh and let people upvote/downvote new services.