Increasing the number of concurrent imap connections allowed from any one IP address

rsleventhal · 07-16-2008, 01:45 PM

Hi all,

I'm running the Parallels Pro X 10.3.0 control panel for web hosting on CentOS 5.2. All's running very well with one minor issue.

I've some heavy-use clients who use a proxy to connect to our mail server, so their outward facing IP is the same for each connection.

It appears that the imap server on my box is hitting a wall after a limit is hit, generating errors on the client side like 'The imap server has terminated the connection' or 'Imap connection limit reached'.

I've put in a ticket with the provider, but am hoping that this knowledgeable community may have an idea on how to increase the concurrent connection limit for IMAP.

Thanks in advance,
-Ray

pruneau · 07-16-2008, 02:22 PM

What is ou imap server to start with ?

rsleventhal · 07-16-2008, 02:46 PM

Hi,

Thanks for the reply...I should have stated this up front.

Sadly, the appliance software (Ensim/Parallels) runs uw-imap. I wish it were courier or dovecot as those are a breeze.

-R

Mr. C. · 07-16-2008, 03:01 PM

Huh... contact your vendor.

rsleventhal · 07-16-2008, 03:02 PM

already have...but was hoping for an insight here.

thanks for the reply, nonetheless

-Ray

pruneau · 07-16-2008, 03:10 PM

Errr, WTF if I may ?!?

Straight from: http://www.washington.edu/imap/docum...on/CONFIG.html

Quote:

UNIX Configuration Notes

The IMAP and POP3 servers are plug-and-play on standard UNIX
systems. There is no special configuration needed. Please ignore all
rumors to the effect that you need to create an IMAP configuration
file.

And then they go straight into source code modification and re-compilation.

Ouch, my friend, ouch. Apparently, unless you can recompile from the source, configuration is not an option.

Or just tell me that there is another uw-imap.

Note to self: _avoid_ uw-imap at _all_ costs for anything serious.

Mr. C. · 07-16-2008, 03:11 PM

Understood, and I didn't intend to be glib. Your options, short of limiting the client's concurrent connections, are essentially none.

The appliance may be light on resources, and thereby has capped the number of concurrent connections, or this could be a "value add" for the vendor. Once you buy into an "appliance", you're at the vendors mercy.

Mr. C. · 07-16-2008, 03:15 PM

Quote:

Originally Posted by pruneau

Errr, WTF if I may ?!?

Straight from: http://www.washington.edu/imap/docum...on/CONFIG.html
And then they go straight into source code modification and re-compilation.

Ouch, my friend, ouch. Apparently, unless you can recompile from the source, configuration is not an option.

Or just tell me that there is another uw-imap.

Note to self: _avoid_ uw-imap at _all_ costs for anything serious.

Its an appliance. Artificial caps are one mechanism vendors use to create different market tiers.

rsleventhal · 07-16-2008, 03:21 PM

Thanks for all the replies. Yes, it is an appliance control panel over CentOS, but I may well modify it to use dovecot as that's the imap server of choice with CentOS/RHEL.

I had already found that little <sneering look> oh so helpful </sneering look> piece of non-information

...thought that I'd post just in case there were docs that hadn't been revealed in a day's worth of googling.

I'll post the results, whatever they were, so that others aren't caught.

Kind regards,
-Ray

rsleventhal · 07-17-2008, 10:06 AM

The answer was far more simple than I though it could be.

One way of doing this was to globally change how xinetd handles concurrent connections from a given source IP. Not my preference, but before I found the better solution, I did the value in xinetd.conf from:

Code:

# Define access restriction defaults
#
#       no_access       =
#       only_from       =
#       max_load        = 0
        cps             = 50 10
        instances       = 50
        per_source      = 10

to

Code:

# Define access restriction defaults
#
#       no_access       =
#       only_from       =
#       max_load        = 0
        cps             = 50 10
        instances       = 50
        per_source      = 20   <----changed this

This isn't optimal as it defines a 100% increase in this value for all services managed by xinetd, not just imap.

Then came the better solution from the software vendor support (finally!)

Quote:

to increase limit per IP for imap you have to add directive 'per_source = 100' into /etc/xinetd.d/wp_imap and /etc/xinetd.d/wp_imaps and restart xinetd. It will override default per_source directive, and increase limit only for imap.

The wp_ prefix indicates a 'webppliance' file, which is a term used by Parallels/Ensim for this product.

Solution works and is far better than having to recompile from source, thereby voiding my ability to obtain support from the vendor.

Thanks to all who offered suggestions...I hope this post helps others who use Ensim/Parallels Pro X v 10.3.x

Regards,
-Ray

Mr. C. · 07-17-2008, 11:20 AM

The simple solutions are always the best.

Don't worry about the per_source increase - its is a cap, not a pre-allocation of resources.

It appears your appliance has some room for tuning - that's very good news for you. And that you vendor came through with a good response is even better news. More timely responses from them might give them the Gold.

Best of luck!

pruneau · 07-18-2008, 08:24 AM

OK, thank you very much for the feedback, since we all learned something, and happy that you had a solution that did not involves paying more !

rsleventhal · 07-18-2008, 10:36 AM

Quote:

Originally Posted by Mr. C.

The simple solutions are always the best.

Don't worry about the per_source increase - its is a cap, not a pre-allocation of resources.

It appears your appliance has some room for tuning - that's very good news for you. And that you vendor came through with a good response is even better news. More timely responses from them might give them the Gold.

Best of luck!

I've been hosting for nearly a decade, and with Ensim as my control panel for most of that time. Ensim support was horribly lacking but since having been picked up by SWSoft (now Paralells) things have gotten far better.

The control panel software is very tunable...which is why I was so puzzled by the first reply (from them, not here) of 'recompile from source, but of course if you do that, we can't support you any longer'.

Their next and rather quick reply was the answer I needed.

On top of all this, I've just changed my business model from colocation of my own machines to leasing a dedicated server from a provider about whom I can't say enough good things.

If anyone out there needs a good, solid and reputable dedicated server provider, I wholeheartedly recommend OLM.NET. I don't work for them. I'm just one of their customers. But they're service is outstanding and their support even more so.

Quote:

OK, thank you very much for the feedback, since we all learned something, and happy that you had a solution that did not involves paying more !

I wholly agree...great to have answers without spending more $$.

Thanks to all who replied and offered help

-Ray