on a quick check I'm thinking one way to do this would be to leverage the one time sessions we already have and instead of dropping the session, downgrading them to a one time one. That way the next request the peer sends is answered without maintaining the invalid session. Would need a bit of work tho.

I'm thinking this as an option to avoid simply dealing with traffic of nodes we -in principle- don't want

Yeah that's a good idea.

imo #250 solves this to a satisfactory degree.

nonetheless, nodes behind NAT in geth for example, will never discover their local node id, and will never get a session. geth sets default IP in enr to localhost if node is started to listen on all interfaces.

if we use this soon to be stable is_reserved method from rust, and treat ENRs that don't verify due to enr-socket != src-socket, as ENRs without a socket, iff they are advertising a reserved IP, then we could safely improve connectivity through out the network.

not sure how geth discv5 treats peers that don't advertise any socket in the ENR, if it lets them have sessions or fails them, based on the assumption that all ENRs contain at least a localhost socket. this would be an unjustified assumption and should be fixed, since what to advertise in the ENR, before IP voting, is not spec'd.