11-11-2008
For example you could have nmap running on some Linux box and check if the applications ports are reachable every second and test it's exit code with $? and just write a log for it. Maybe put that Linux PC in the same net like one of the clients having that problem, just to make the network environment the same.
Also you could check if your box has any performance (have a vmstat 1 running and when they call that it happened, check it) problems or shows network errors or something like that. Do the people get disconnected while other people or applications can still communicate with the app?
Maybe you can check the switches/routers that are in between the clients to your server for errors too.
Also the app guys should show their log for the time when this/these disconnect(s) happen. Maybe their app is reporting something.
Maybe it's also the same users every time or some kind of pattern noticeable like that only users from some subnet have this problems or with some sort of workstation?
What kind of application is running there?
Edit: You could also have tcpdump running and search it with ethereal/wireshark.
Last edited by zaxxon; 11-11-2008 at 07:53 AM..
Reason: Added info
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LEARN ABOUT DEBIAN
ovs-vlan-test
ovs-vlan-test(1) Open vSwitch Manual ovs-vlan-test(1)
NAME
ovs-vlan-test - check Linux drivers for problems with vlan traffic
SYNOPSIS
ovs-vlan-test [-s | --server] control_ip vlan_ip
Common options:
[-h | --help] [-V | --version]
DESCRIPTION
The ovs-vlan-test utility has some limitations, for example, it does not use TCP in its tests. Also it does not take into account MTU to
detect potential edge cases. To overcome those limitations a new tool was developed - ovs-test. ovs-test is currently supported only on
Debian so, if possible try to use that on instead of ovs-vlan-test.
The ovs-vlan-test program may be used to check for problems sending 802.1Q traffic which may occur when running Open vSwitch. These prob-
lems can occur when Open vSwitch is used to send 802.1Q traffic through physical interfaces running certain drivers of certain Linux kernel
versions. To run a test, configure Open vSwitch to tag traffic originating from vlan_ip and forward it out the target interface. Then run
the ovs-vlan-test in client mode connecting to an ovs-vlan-test server. ovs-vlan-test will display "OK" if it did not detect problems.
Some examples of the types of problems that may be encountered are:
o When NICs use VLAN stripping on receive they must pass a pointer to a vlan_group when reporting the stripped tag to the networking
core. If no vlan_group is in use then some drivers just drop the extracted tag. Drivers are supposed to only enable stripping if a
vlan_group is registered but not all of them do that.
o On receive, some drivers handle priority tagged packets specially and don't pass the tag onto the network stack at all, so Open
vSwitch never has a chance to see it.
o Some drivers size their receive buffers based on whether a vlan_group is enabled, meaning that a maximum size packet with a VLAN tag
will not fit if no vlan_group is configured.
o On transmit, some drivers expect that VLAN acceleration will be used if it is available, which can only be done if a vlan_group is
configured. In these cases, the driver may fail to parse the packet and correctly setup checksum offloading or TSO.
Client Mode
An ovs-vlan-test client may be run on a host to check for VLAN connectivity problems. The client must be able to establish HTTP connec-
tions with an ovs-vlan-test server located at the specified control_ip address. UDP traffic sourced at vlan_ip should be tagged and
directed out the interface whose connectivity is being tested.
Server Mode
To conduct tests, an ovs-vlan-test server must be running on a host known not to have VLAN connectivity problems. The server must have a
control_ip on a non-VLAN network which clients can establish connectivity with. It must also have a vlan_ip address on a VLAN network
which clients will use to test their VLAN connectivity. Multiple clients may test against a single ovs-vlan-test server concurrently.
OPTIONS
-s, --server
Run in server mode.
-h, --help
Prints a brief help message to the console.
-V, --version
Prints version information to the console.
EXAMPLES
Display the Linux kernel version and driver of eth1.
uname -r
ethtool -i eth1
Set up a bridge which forwards traffic originating from 1.2.3.4 out eth1 with VLAN tag 10.
ovs-vsctl -- add-br vlan-br
-- add-port vlan-br eth1
-- add-port vlan-br vlan-br-tag tag=10
-- set Interface vlan-br-tag type=internal
ifconfig vlan-br-tag up 1.2.3.4
Run an ovs-vlan-test server listening for client control traffic on 172.16.0.142 port 8080 and VLAN traffic on the default port of 1.2.3.3.
ovs-vlan-test -s 172.16.0.142:8080 1.2.3.3
Run an ovs-vlan-test client with a control server located at 172.16.0.142 port 8080 and a local VLAN ip of 1.2.3.4.
ovs-vlan-test 172.16.0.142:8080 1.2.3.4
SEE ALSO
ovs-vswitchd(8), ovs-ofctl(8), ovs-vsctl(8), ovs-test(8), ethtool(8), uname(1)
Open vSwitch December 2010 ovs-vlan-test(1)