Re: NFSv4 referrals - custom (non-2049) port numbers in fs_locations?

[Chuck Lever III <chuck.lever@oracle.com>]

> On Feb 5, 2024, at 11:17 AM, Trond Myklebust <trondmy@hammerspace.com> wrote:
> 
> On Mon, 2024-02-05 at 15:13 +0000, Chuck Lever III wrote:
>> 
>> 
>> A DNS label is just a hostname (fully-qualified or not). It
>> never includes a port number.
>> 
>> According to RFC 8881, fs_location4's server field can contain:
>> 
>>  - A DNS label (no port number; 2049 is assumed)
>> 
>>  - An IP presentation address (no port number; 2049 is assumed)
>> 
>>  - a universal address
>> 
>> A universal address is an IP address plus a port number. Therefore
>> a universal address is the only way an alternate port can be
>> communicated in an NFSv4 referral.
> 
> That's not strictly true. RFC8881 has little to say about how you are
> to go about using the DNS hostname provided by fs_locations4. There is
> just some non-normative and vague language about using DNS to look up
> the addresses.
> 
> The use of DNS service records do allow you to look up the full IP
> address and port number (i.e. the equivalent of a universal address)
> given a fully qualified hostname and a service. While we do not use the
> hostname that way in the Linux NFS client today, I see nothing in the
> spec that would appear to disallow it at some future time.

We absolutely could do that. But first a service name would need to be
reserved, yes?

https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml?search=dns


--
Chuck Lever