the persistent idiocy of "privileged ports" on Unix
TCP and UDP have ports. These are 16 bit; there are 65535 or so per IP address. These protocols don't care to differentiate between the ports. Elsewhere, IANA presumes to operate a process to allocate "well-known" ports in the range 1-1023, "registered ports" in the range 1024-49151, and to reserve the remainder, 49152–65535, for "ephemeral" ports. The caller end has to have a port, which is how replies get back within the virtual connection, and these are conventionally picked from the ephemeral range by the OS's networking stack. The whole idea of ports is ridiculous, because it allows ISPs to arse around presuming to decide which services they will "not allow". Anything that allows IPSs to do anything other than shift opaque packets will allow ISPs to meddle and break things, and due to the Law of Meddling, if they can, they will. I am currently working around an issue with Claro, a pretend ISP, blocking port 5060, allocated to SI...
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