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Subject: RE: multiple servers on the same (loopback) interface
From: Mark Rivers <rivers@cars.uchicago.edu>
To: "'Jameson Graef Rollins'" <jrollins@ligo.caltech.edu>, "Kasemir, Kay" <kasemirk@ornl.gov>, "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Tue, 9 Jul 2013 18:46:57 +0000
This is probably the problem of DNS resolution timing out because there is no DNS server to do the reverse DNS lookup on that interface.

Mark


-----Original Message-----
From: tech-talk-bounces@aps.anl.gov [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Jameson Graef Rollins
Sent: Tuesday, July 09, 2013 1:42 PM
To: Kasemir, Kay; tech-talk@aps.anl.gov
Subject: Re: multiple servers on the same (loopback) interface

On Tue, Jul 09 2013, "Kasemir, Kay" <kasemirk@ornl.gov> wrote:
> The first IOC will serve on TCP port 5065.
> The second one can't do that, so you get the warning Configured TCP port was unavailable, ...Using dynamically assigned TCP port 34497.
> Both will try to listen to UDP search requests on the same port, then reply with the TCP port that they actually use, so all should be fine.
>
> BUT: Because of a quirk in most network kernels only one of them will actually see those UDP search requests. For me it's usually the IOC started _last_.
>
> If you want your clients to send search requests to all IOCs that are listening on the UDP port, you need to send a broadcast. Search requests sent to a specific IP address will only reach one of the IOCs listening on that IP.
>
> You can try setting the EPICS_CA_ADDR_LIST=255.255.255.255.
> With localhost, that may not be possible, so you'll have to setup some network interface, maybe leave it disconnected, but it must have an IP address and most important a broadcast address.

Hi, Kay.  Thanks for the suggestion.  This is a possibility that I
considered, but since it requires administrative privileges to create
and configure the dummy interface it's less than ideal for a generic
testing infrastructure.

That said, I did give it a try and it does sort of work.  The dummy
interface is 127.2.0.1, and both servers bind to it.  However, the
client access is very slow:

0$ time EPICS_CA_ADDR_LIST=127.255.255.255 EPICS_CA_AUTO_ADDR_LIST=NO caget -t TEST0:FOO
0

real	0m6.292s
user	0m0.000s
sys	0m0.012s
0$

The initial response is fairly quick, but there's a long delay before
process returns.  Is using a broadcast address know to introduce a
noticeable delay like this?

jamie.


Replies:
RE: multiple servers on the same (loopback) interface Jameson Graef Rollins
Re: multiple servers on the same (loopback) interface D Peter Siddons
References:
multiple servers on the same (loopback) interface Jameson Graef Rollins
Re: multiple servers on the same (loopback) interface Kasemir, Kay
Re: multiple servers on the same (loopback) interface Jameson Graef Rollins

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