Does HTTPS use TCP or UDP?
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6 Answers
HTTPS can run over any reliable stream transport protocol. Normally that's TCP, but it could also be SCTP. It is NOT expected to run over UDP, which is an unreliable datagram protocol (in fact, while that's not its official name, that's a good way to remember what it is).
The IANA assignment for UDP is historical; at the time, nearly every protocol was assigned both the TCP and UDP port numbers, even if it was expected that it would only ever use one. There has been discussion of merging the port number registries, and only ever assigning one port to one protocol from here on. That is to make it easier to deploy future transport protocols that would otherwise need their own registries. I'm not aware of how that discussion concluded.
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1Most SSL implementations expose it as SSL socket, so it implies TCP. There are very rare occurrences of using any other transport.– NaskoCommented May 14, 2010 at 18:10
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4Warning: this answer is outdated (9 years ago). Take a look at the answer about QUIC protocol, which is an implementation that Google uses for Chrome. Just saying. Commented Feb 26, 2018 at 20:24
It uses TCP. It would be difficult to run it on UDP without the guarantee of packets arriving. If the packets don't arrive, the encrypted data will not be decipherable.
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4Or if the packets arrive out of order, as UDP contains no provisions for reordering packets like TCP.– jannebCommented Jan 3, 2010 at 9:42
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3Not going to -1 you because it'd be a little pedantic, but its worth noting that there's no reason it couldn't be run over UDP. It may be atypical, but it is possible. Commented Jan 3, 2010 at 12:01
Nowadays HTTPS can run above either TCP or UDP.
The new "QUIC" protocol aims to replace multiple TCP connections with one multiplexed UDP connection, and hence can handle SSL and HTTPS:
HTTPS → SSL → QUIC flow → UDP → IP
QUIC was originally developped in 2012 by Google and is undergoing IETF review. For more details, see Wikipedia.
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1This should be the answer, considering the current scenario. For example, for experimental purposes, I could only block HTTPS traffic for an specific IP, using
DROPtargets onmangletable, usingudpprotocol for the rule. Commented Feb 26, 2018 at 20:22 -
3+1, did not expect to learn something when clicking on this question. Commented Jun 25, 2018 at 17:21
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+1 to @T.Coutlakis When I was going through the output of
cat /etc/services, I came across "https 443/udp # HTTP/3", which got me wondering about HTTPS over UDP.– ZeZNiQCommented Jun 18, 2023 at 15:59
For the next time, if you wonder if a default port service run on tcp or udp, you can look at /etc/services on a linux machine.
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3Or a Windows machine, in a command prompt:
find "https" %windir%\system32\drivers\etc\servicesCommented Jan 3, 2010 at 11:57 -
1My /etc/services also lists 80/udp. Actually, many services have allocated both ports, "just in case" I guess. Commented Jan 9, 2010 at 23:03
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Here's what /etc/services has to say about this method: "officially ports have two entries even if the protocol doesn't support UDP operations."– De NovoCommented Sep 26, 2020 at 19:19
The OSI model allows higher layer protocols to run over any underlying protocol providing the correct services. HTTPS is HTTP using SSL/TLS security. SSL/TLS typically runs on top of TCP, but there is nothing to stop you from running it on UDP, SCTP or any other transport layer protocol.
As a matter of fact HTTPS over TCP and UDP are both defined as "well known" by IANA and have reserved port numbers.
See http://www.iana.org/assignments/port-numbers for the "official" ports/protocol combinations.
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1See for example tools.ietf.org/html/rfc4347 (Datagram Transport Layer Security) for how SSL/TLS can run over UDP.– pehrsCommented Jan 3, 2010 at 11:35
answered May 21, 2018 at 22:34
