Tor relays reject UDP packets except DNS requests. What is the technical reason behind that UDP is not routed through Tor circuit? Are there limitations with UDP protocol that it cannot be routed through Tor? Is there a problem with implementation design of Tor that it cannot support UDP?

Is UDP being connectionless protocol a problem? If this is a problem it cannot support UDP then how DNS requests are supported?


1 Answer 1


Well, DNS queries are made via TCP - Tor does not use UDP at all, strictly speaking. The resolving query from the exit node - yes, it can be made through UDP protocol, but it's totally up to the resolver libraries and settings on the exit node's host - Tor does not deal with it at all. DNS service inside Tor itself - the one you're configuring via DNSxxxx directives - it's rather a stub, than something that can be called a full DNS service. And about routing UDP in Tor network - actually, there's no technical blocker to use UDP, it's just limited "by design" of Tor's architecture. It has it's PROs and CONs - but the limit is just an architectural one

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