[PD-dev] Requesting SVN commit access

[IOhannes m zmoelnig]

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(taking this back to the list)

On 2014-02-26 14:55, Martin Peach wrote:
> On 2014-02-26 03:47, IOhannes m zmoelnig wrote:
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>> 
>> On 2014-02-26 04:57, Martin Peach wrote:
>> 
>> 
>> how come? how does DNS (after all, a central service in the
>> internet) work with this assumption?
>> 
>> UDP works fine with as a challenge/response system (less so as 
>> client/server, given that there is no notion of a "connection"),
>> and for responses you need o be able to send messages somewhere.
>> 
>> for whatever reasons, many hardware manufacturers have the idea
>> that sending/receiving on the *same* port is a good idea.
> 
> I see; but for DNS with [udpsend] and [udpreceive], it should work
> since one [udpsend] can send to port 53 of the DNS server and a
> separate [udpreceive 53] will receive its replies.


it seems i was a bit unclear here, and thus two separate things got
mixed up:

 - DNS
is a bi-directional protocol: you send a query (from a random port N)
to a DNS-server (on port 53), and the server sends a response from
port 53 to that port N.

 - hardware-manufacturers
like the idea that the receiving port is the same as the sending port.

DNS does not have this limitation of using the same port (thus you can
query a DNS-server on localhost without stepping on your own ports).
so having both [connect dns.server 53(->[udpsend] +  [udpreceive 53]
is not sufficient to query a DNS-server.

> The problem seems to be that [udpsend] will assign itself a random
> port to which the remote device will send replies, but [udpsend]
> doesn't know its own port number.

well, but that's only half of the solution (for the DNS-problem):
even if [udpsend] had a notion of it's sending port, it would discard
all messages arriving on this port. but it still *listens* on (and
thus blocks) this port, so you cannot tell a [udpreceive] to (also)
use it.

fg,asd
IOhannes
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