TCP and UDP Port 0 - Should an ISP or ITP Block it?

Tue Aug 25 12:48:27 UTC 2020

On Tue, 25 Aug 2020 12:40:43 +0000
Pim van Stam <pim at vanstam-ict.nl> wrote:

> Ohter opinions on this?

IETF RFC 768 - User Datagram Protocol weighs in:

  "Source Port is an optional field, when meaningful, it indicates the
  port of the sending  process,  and may be assumed  to be the port  to
  which a reply should  be addressed  in the absence of any other
  information.  If not used, a value of zero is inserted."

In practice however, most applications I've seen that do not expect a
response still set a non-zero value (e.g. flow-export, syslog).

John