[Nagiosplug-devel] check_http: Socket timeout after 10 seconds (but webserver is up! )

[Paul Boot - Bateau Knowledge]

Non Nagios related but people can benefit from this:

I did some test with Linux VLAN tagging with a modified 3com905 ethernet
driver and a Cisco 2924XL switch. You have to modify your ethernet driver
because the VLAN tagging adds 4 extra bytes to each ethernet PDU.(thus
allowing oversize ethernet packets)

Recompile the driver as a kernel module or include it in your kernel.

You can test if it works with a simple ping.

I will send Christoph a word document with all Linux VLAN related
documentation I could find.

Kind regards,

Paul Boot.


----- Original Message -----
From: "Christoph Stotz" <stotz at logo.de>
To: "'Subhendu Ghosh'" <sghosh at sghosh.org>; <pb at bateauknowledge.nl>;
<karl at debisschop.net>
Cc: <nagiosplug-devel at lists.sourceforge.net>
Sent: Saturday, February 08, 2003 4:56 PM
Subject: RE: [Nagiosplug-devel] check_http: Socket timeout after 10 seconds
(but webserver is up! )


> Hello,
>
> first of all thank you very much for trying to help. Unfortunately I found
> out right know, that the problem I am experiencing is not directly caused
by
> the check_http plugin. The whole trouble is caused by the VLAN (802.1q)
> feature I am using on the monitoring server. For those of you who do not
> know what that is, you might want to have a look to the following two
links.
> There it's explained quite well:
>
>
ftp://ftp.netlab.ohio-state.edu/pub/jain/courses/cis788-97/virtual_lans/inde
> x.htm
> http://www.candelatech.com/~greear/vlan.html
>
> The short version of the explanation is: using VLAN "tagging" you are able
> to have several "virtual" ethernet devices connected by a single physical
> ethernet device (of course sharing the available bandwidth). In my case
this
> allows me to monitor different trunks of my network directly without
having
> to pass by a firewall or router. The alternative to that is to mount
> multiple NIC's (in my case multiple quad-NICs).
>
> If you go and have a look to the second link I just posted in this
message,
> you will read
>
> "MTU problems exist for many ethernet drivers. Other than that, things
seem
> fairly stable! "
>
> Well - that is exactly what I am experiencing. The whole thing is stable,
> but I am experiencing a MTU-Problem. As soon as the webserver I want to
> check with check_http is located on a VLAN trunk and returning more than
> 1476 bytes of data to the check_http, the packet gets either malformed or
> fragmented. Due to an issue with the ethernet kernel driver, those
returning
> fragments are not put together properly and therefore check_http times out
> with a Socket error.
>
> So, this is an issue for the VLAN mailing list rather than the
> nagiosplug-devel mailing list. If you experience this problem, the VLAN
> mailing list located at
>
> http://www.wanfear.com/mailman/listinfo/vlan
>
> might be a good point to start. By the way I am using a 3c905C-TX/TX-M
> [Tornado] rev 78 NIC with the 3c59x module version LK1.1.16 (19 July
2001).
>
>
> If I solve the issue, I will let you know how.
>
>
> Thanks again.
>
>
> Kind Regards
>
> Christoph Stotz
>
>
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