Which kinds of relaying Tor servers are available as "rendezvous points" and "introduction points" for hidden services?

Question

There appears to be several kinds of nodes (Tor instances acting as servers relaying traffic for others):

• Clients with Relaying disabled (Included in this list only for completion, as their IPs are not published, so they cannot be used).

• Private bridges (I presume these cannot be used as "rendezvous points" and/or "introduction points" as their IPs are not published?)

• Public bridges (I am not sure if these are actually configured any differently than the line below (Middle Relays)).

• A Relay with exit policy reject *:* (these servers IPs have their IPs published, so perhaps they qualify for use as "rendezvous points" and/or "introduction points"?)

• Exit nodes (these servers IPs have their IPs published, so perhaps they qualify for use as "rendezvous points" and/or "introduction points"?)

• Any others that I missed?

I am interested in discovering what qualifies and or disqualifies a node for use as an "introduction point."

And I am equally as interested in discovering what qualifies and or disqualifies a node for use as an "rendezvous point."

Based on my reading of the documentation I currently believe that "introduction points" are all hosted on exit nodes, and "rendezvous points" will only choose a "Relay with exit policy reject *:* (middle nodes)"

Answer 1

First of all, we don't usually refer to Tor instances running as clients as nodes. Nodes are relays, and unless specifically said otherwise, it usually also excludes bridge relays. So nodes are any instances of Tor that are in the public consensus.

For introduction points, tor picks nodes that are stable (which was previously called having high uptime).

For circuits to the rendezvous points, we pick nodes that are fast -- e.g. in rend_service_introduce().