nanog mailing list archives
Re: TCP and UDP Port 0 - Should an ISP or ITP Block it?
From: Matthew Petach <mpetach () netflight com>
Date: Tue, 25 Aug 2020 12:11:46 -0700
On Tue, Aug 25, 2020 at 8:36 AM Mel Beckman <mel () beckman org> wrote:
“SHOULD” is not “SHALL”, and thus this doesn’t countermand RFC 768’s instruction “ If not used, a value of zero is inserted." So the key question is, when is the source port not used? When a reply is not requested, is my thinking. Is there an application that implements this in UDP? (it’s nonsensical in TCP, which always requires a handshake, after all). I don’t recall one, but I can envision one: sending a one-way notification that requires no acknowledgement.
There are many applications that send UDP streams that don't expect a reply. Here's one I worked on at previous $DAYJOB: https://github.com/yahoo/UDPing It emits a stream of UDP packets to a measurement box, which collects the data and reports statistics on it. No replies to the UDP probes are sent. But there's another, more common application that many people on this list use every day, and indeed was likely the initial trigger for this thread: netflow collection. Your routers emit UDP data streams, destined for a netflow collector box; no reply is expected (and indeed, no reply is desired; the router is busy enough *sending* the netflow stream, trying to process replies would just be another burden on the CPU). [...]
I think filtering zero-sourced UDP flies in the face of fundamental Internet interoperability. -mel
Indeed. There are existing applications where the source port of unidirectional UDP streams is not used, as no replies are expected, and may be left as zero. Matt
Current thread:
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it?, (continued)
- Message not available
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? John Kristoff (Aug 25)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Tom Beecher (Aug 25)
- Message not available
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? K. Scott Helms (Aug 26)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Nick Hilliard (Aug 26)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? K. Scott Helms (Aug 26)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Töma Gavrichenkov (Aug 25)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Douglas Fischer (Aug 25)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Mel Beckman (Aug 25)
- Re: TCP and UDP Port 0 - Should an ISP or ITP Block it? Matthew Petach (Aug 25)
- RE: TCP and UDP Port 0 - Should an ISP or ITP Block it? adamv0025 (Aug 25)