[ntp:questions] Source address in response always the same as target address in request?
David L. Mills
mills at udel.edu
Fri Dec 14 18:06:29 UTC 2007
Brian,
I recall the SHOULD was inserted to support the anycast model where any
of a number of servers could respond to a specific request. NTP along
with many others in the late 1970s did not anticipate such a model and,
even if they did, as later in NTP manycast, the addresses are still
necessary for operation sugbsequent to discovery.
Dave
Brian Utterback wrote:
>
> Danny Mayer wrote:
>
>>Brian,
>>
>>UDP is stateless. There is absolutely no way that the UDP protocol
>>developers could require that that a reply go back to the same address
>>from which the packet was sent or that it be sent from the same IP
>>address. No reply is ever required of a datagram. It would be a protocol
>>layering violation to do so.
>
>
> And yet the host requirements RFC does so require it, at least to
> the "SHOULD" level:
>
> When the local host is multihomed, a UDP-based request/response
> application SHOULD send the response with an IP source address
> that is the same as the specific destination address of the UDP
> request datagram.
>
> My contention is that although it is a SHOULD, the sockets API did
> not provide a way to actually accomplish it, so very few UDP
> protocols do not deal with the failure to do so. Except NTP.
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