Re: Redundant work using udprelay

Karl J. Runge (runge@redhook.llnl.gov)
Fri, 18 Apr 97 23:31:42 PDT


On Fri, 18 Apr 1997, "Christian Foisy (7086)" <cfoisy@gauss.chimie.USherb.ca> wrote:
>
> Right now I'm using idle periods on our SP2 with communication going
> trough udprelay. It's working except for the following "problem": when
> many copies of the program are launched in parallel, each one of them
> receives the same block of keys to test. At the next iteration,
> everything is ok as they will receive different blocks. Is there a way
> to avoid or shorten this redundant period? (I usually have only short
> idle slots)

I think this is because the keyserver uses (host:port) as an identifier
for a single client process. Perhaps udprelay reuses the same open socket to
the keyserver for the multitude of clients starting at the same time?

When I was writing some perl scripts to redirect the udp traffic thru my
broken slip emulator using tcp sockets, Rocke suggested the following to me:

> However, there is some state information maintained at the server you
> need to be aware of. If you plan for this it shouldn't be much harder.
> If you don't plan for this, it will cause you or I some grief...
>
>
> Remember the fault-tolerance. [If a client doesn't get an answer, it
> resends the same packet.]
>
> Likewise, if the server receives the same packet from a given IP:port,
> it usually resends the same response. [I have found out the hard way
> that with assymetric routes in the Internet, I will often get duplicate
> requests for keyspace over and over and over, sometimes for hours on
> end.]
>
> For your gateway to work correctly, and not adversely impact the server,
> your gateways need to make sure there is a 1:1 correspondence between
> the host:port you present to my server and the real host:port on the
> isolated side of the gateways.
>
> Specifically: Do NOT automatically allocate a new system-assigned UDP
> port at the Internet side of the gateway each time you send a packet
> to the server.
>
> Specifically: DO allocate a new UDP port at the Internet side of the
> gateway each for each different private-side host:port.

Does anyone know what the algorithm udprelay uses? Is it possible it
can confuse the keyserver in any other ways?

Karl

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Karl J. Runge -- Linux: it's the Real thing -- runge@crl.com
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