How not to design a wire protocol

[Eric S. Raymond]

Daniel Franke <dfoxfranke at gmail.com>:
> On Tue, Mar 5, 2019 at 1:52 PM Eric S. Raymond <esr at thyrsus.com> wrote:
> > If you end up going with a non-123 port number, I requst that the RFC
> > allow use on other ports when and if ALPN is available and specify
> > the ALPN tag to be used.
> 
> The spec already mandates that ALPN always be used and allocates a tag
> with IANA.

Thanks.  I didn't see that in the RFC draft.  Did I simply miss it or is
it in a registry that is entirely separate?

> > I disagree.  New firewall holes are difficult, practically if not
> > theoretically.
> 
> tcp/123 is already a new firewall hole. If you want to work around
> unchangeable firewall rules you probably have to use 443 (and again
> rely on ALPN).

Whether TCP on a port with an existing UDP hole would be treated as "new"
is probably variable by firewall default and administrative policy.  At the
very least I expect it to lower a psychological barrier, especially when the
TCP service has a clear relationship to the UDP one.
-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

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