[ntp:questions] client behind NAT (low-port bug)

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Mon Apr 16 20:55:44 UTC 2012


Jason Lixfeld wrote:
> The main issue here is that the NAT box ahead of my
>  internal NTP server changes the source port of the
>  output NTP request to some low port < 123,
>  which ntpd seems to reject.
> Modifying the configuration on my NAT box may be an option as well.

If you believe in RFCs
 {which without at least something similar,
   the internet would not have progressed as far
   in usefullness or be as useable by so many}

 If NTP is NOT using the Well Known System Port Assigned Number 123,
  if should be using a User Port Number 1024-49151,
  or a Dynamic / Ephemeral Port 49152-65535?

<BlockQuote> IP Network Address Translator (NAT) Terminology and Considerations
2.4. TU ports, Server ports, Client ports

   For the reminder of this document, we will refer TCP/UDP ports
   associated with an IP address simply as "TU ports".

   For most TCP/IP hosts, TU port range 0-1023 is used by servers
   listening for incoming connections. Clients trying to initiate a
   connection typically select a source TU port in the range of 1024-
   65535. However, this convention is not universal and not always
   followed. Some client stations initiate connections using a source TU
   port number in the range of 0-1023, and there are servers listening
   on TU port numbers in the range of 1024-65535.

   A list of assigned TU port services may be found in RFC 1700 [Ref 2].
</BlockQuote> <http://tools.ietf.org/html/rfc2663>

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