Talk:Ephemeral port

Dynamic ports

Is dynamic port a synonym. Port number says "The dynamic or private ports are those from 49152 through 65535. One common use is for ephemeral ports." what are the other uses? --Kvng (talk) 17:25, 13 March 2011 (UTC)

Ephemeral literally means short-lived and that term is often used interchangably with dynamic, even in the IETF RFC specifications (see IETF RFC 6335 for instance). However, the IANA port registry documents the dynamic port range to be 49152-65535 inclusive. In practice, systems can and do allocate a dynamic (aka ephemeral) port outside of this range. Likewise, service applications, that is servers could listen on a port assigned to a number in that IANA defined range. The IANA registry describes a guideline and common use, but there is nothing to stop anyone from using them differently, but it is not a common practice. --jtk (talk) 21:15, 7 August 2014 (UTC)

is this correct

That does the following mean. The way I understand it this is not correct:

Ephemeral ports may also be used to free up a well-known service listening port and establish a service connection to the client host.

I do not believe it is possible to change a port number once a connection is made, from my looking at wire-shark traces I have never seen it. Further more the use of ephemeral ports makes it unnecessary. The limit of the number of client to connect to a single service on a single ip (e.g. port 80 on 91.198.174.232) is number-of-ephemeral-ports per client.

Why a limited set of ephemerals

(can someone review this it is just my trying to work it out.) Is it that if we let port used by services e.g. 80 be used as an ephemeral on a device that is also a server, serving for example on port 80. Then we may get in a situation where ip=A ephemeral=80 connects to ip=B port=80, and then it may happen that ip=B ephemeral=80 attempts to connect to ip=A port=80, the connection will be refused (though this it least in theory con be detected at the client, and a new ephemeral assigned automatically before a connection is attempted). We could allow all ports not used as services be used as ephemerals, but this is harder to manage and why bother when there are so many spare dynamic ports. I

A port, ephemeral or otherwise is just one part of the 5-tuple (source address, destination address, protocol, source port, destination port) that identifies process-to-process communications. It is perfectly acceptable and common for one host to use the same local port and correctly disentangle communications as long as some of the 4 components of the tuple are distinct. If this were not the case, a web server server listening on port 80 would not be able to handle multiple conversations from remote clients. However, in practice an ephemeral source port selection strategy will not select a local port already in use by another process, even if resultant communications means the 5-tuple properties are otherwise different. Furthermore, in your specific example, at least on UNIX-based systems, but this is generally true in others, port numbers below 1024 are well-known or "privileged" and generally not available except by root or administrative processes so you won't generally find them being part of the ephemeral source port pool. --jtk (talk) 21:15, 7 August 2014 (UTC)

Configuration characteristics

"If certain server software is used, that uses non ephemeral custom port ranges"

Is this server software installed on the client machine? More context is needed in this section in my opinion. Elirankoren (talk) 12:20, 25 October 2019 (UTC)