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limit to number of consoles?

 

 

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john at iastate

Oct 22, 2007, 9:55 AM

Post #1 of 4 (2500 views)
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limit to number of consoles?

I'm sure there must be a limit somewhere.
If nothing else there are only about 64K tcp ports,
but I'm wondering of there is some much lower limit
that I will run into first? Right now we are at
667 consoles and growing. Is this something I need
to worry about soon or do I have plenty of "headroom"?


Thanks,
John
PS, our devices are mostly connected through cyclades
terminal servers in raw mode, but we do have some
using LAT terminal servers and a few connected via
a USB-serial adapter. We are trying to phase out
the LAT TSs owing to their age and scarcity (perhaps
we are the worlds largest repository of DECserver 90s
at this point :)
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david.k.harris at siemens

Oct 22, 2007, 3:00 PM

Post #2 of 4 (2357 views)
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RE: limit to number of consoles? [In reply to]

I know a few shops with more than 2k console ports...so we both have a
fair bit of headroom... but, thanks for clarifying your point. That's
probably a valid thought, unless the code were doing something seriously
stateful, where it could use the same listener for many different IPs,
and use the IP to keep the conversations straight. I don' tthink that's
the (current) case.)

-Z-

-----Original Message-----
From: John Hascall [mailto:john [at] iastate]
Sent: Monday, October 22, 2007 2:28 PM
To: Harris, David (IT Solutions US)
Subject: Re: limit to number of consoles?

> Hmmm... the number of TCP ports isn't usually an issue, as the
> connections are often made across multiple devices, i.e.;
>
> Console 1 TS-1 port TCP 7001
> Console 1 TS-1 port TCP 7002
> Console 1 TS-1 port TCP 7003
> Console 1 TS-1 port TCP 7004
> Console 1 TS-2 port TCP 7001
> Console 1 TS-2 port TCP 7002
> Console 1 TS-2 port TCP 7003
> Console 1 TS-2 port TCP 7004
> Console 1 TS-3 port TCP 7001
>
> So, clearly a re-use of the TCP port, spread across many IP
addresses
> for the assorted console servers.

That's the port number on the remote end. Each one of those
connections is using a port# on the conservere end too. For
example:

delos: {1} netstat -an | grep 7001
tcp 0 0 172.17.2.254.59046 172.17.2.14.7001
ESTABLISHED
tcp 0 0 172.17.2.254.59081 172.17.2.11.7001
ESTABLISHED
tcp 0 0 172.17.2.254.59106 172.17.2.13.7001
ESTABLISHED
tcp 0 0 172.17.2.254.59195 172.17.2.12.7001
ESTABLISHED
tcp 0 0 172.17.2.254.50994 172.17.2.3.7001
ESTABLISHED
tcp 0 0 172.17.2.254.51007 172.17.2.2.7001
ESTABLISHED
tcp 0 0 172.17.2.254.51021 172.17.2.1.7001
ESTABLISHED
^^^^^
local ports (1024-65535 available)

> You can also mix-and-match console servers, using some of the
> DECservers, adding newer units from other vendors, simply replacing
the
> TCP ports used by that vendor. :-)
>
> The limits you need to think about are how much disk space for log
> storage (include retention time in your calculations...), and RAM for
> enough children processes. :-)

We're good there.

I was mostly worried about some unknown to me internal limit
(a table size or something), but I see at least one person
has 3x the consoles I do, so for the present I see nothing
to worry about.


Thanks,
John
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bryan at conserver

Oct 22, 2007, 5:20 PM

Post #3 of 4 (2364 views)
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Re: limit to number of consoles? [In reply to]

there shouldn't be any internal limits any more. back in revisions
there certainly was...and you had to build conserver with those limits
specified. but now it'll grow until it buries the server by using up
all available resources (ram, cpu, ports, whatever). if you're spawning
off commands as consoles, then you could use up pseudo-ttys. process
limits could be an artificial limit (which are adjustable, of course)
and things like ram usage, cpu usage, port usage, etc would be other
limits which are harder to deal with. but on any semi-recent (or even
fairly old) system you should be able to handle thousands of consoles
without much trouble.

that being said, startup times, responsiveness, and such might coerce
you into multiple conserver hosts to help spread out any pain (or for
local connectivity in case of network outages, etc). i won't claim it's
the most efficient code, but it tries fairly hard to deal lots of
consoles and my personal goal is to allow/support/deal with large
installations.

hope that gives you what you're looking for...

Bryan
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sommerfeld at sun

Oct 22, 2007, 8:22 PM

Post #4 of 4 (2366 views)
Permalink
RE: limit to number of consoles? [In reply to]

On Mon, 2007-10-22 at 15:00 -0700, Harris, David (IT Solutions US)
wrote:
> Each one of those
> connections is using a port# on the conservere end too. For
> example:
>
> delos: {1} netstat -an | grep 7001
> tcp 0 0 172.17.2.254.59046 172.17.2.14.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.59081 172.17.2.11.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.59106 172.17.2.13.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.59195 172.17.2.12.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.50994 172.17.2.3.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.51007 172.17.2.2.7001 ESTABLISHED
> tcp 0 0 172.17.2.254.51021 172.17.2.1.7001 ESTABLISHED

There's no actual requirement in the TCP protocol that the local port be
unique for an outgoing connection; it's the 4-tuple (local address,
local port, remote address, remote port) which uniquely identifies the
connection.

The system I'm most familiar with -- Solaris -- was fixed about two
years ago to do controlled reuse of local ports to permit more
connections than the available anonymous port range permits.

The easiest way to demonstrate this feature is to artificially constrain
the available anonymous port space:

# ndd -set /dev/tcp tcp_smallest_anon_port 32768
# ndd -set /dev/tcp tcp_largest_anon_port 32770

and then make a few outgoing connections to web servers:

% netstat -n -finet | grep 10.8.57 | grep 80
129.148.174.66.32768 10.8.57.1.80 32811 0 502094 0 ESTABLISHED
129.148.174.66.32768 10.8.57.2.80 32811 0 502094 0 ESTABLISHED
129.148.174.66.32768 10.8.57.3.80 49232 0 501008 0 ESTABLISHED

The default 2^15 anonymous ports available can make many more than 2^15
outgoing connections.

(this was bug 4461538; the fix is in the current development builds aka
sunos 5.11 or solaris "nevada").

- Bill













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