[Thinstation-developer] [Fwd: [Thinstation-general] Solved: DHCP problems]

[Kanwar R. S. <m3...@ro...>]

It's better here then in the general list...

-------- Forwarded Message --------
From: Jason Meers <Jas...@mv...>
To: thinstation general <thi...@li...>
Subject: [Thinstation-general] Solved: DHCP problems
Date: Thu, 20 Jul 2006 14:14:33 +0100

Yesterday we lost power completely to our offices. The power went a 
couple of times in close succession throughout the day.

I lost approx 100 TS clients for an hour because nobody could get a DHCP 
address. After a lot of troubleshooting the problem was identified as 
our old friend "spanning-tree protocol".

For some reason when the power came back on all of our network switches 
had reverted back to factory defaults. Not only had spanning tree 
protocol been enabled on all of our switches, but our switches were now 
using DHCP addresses themselves instead of the fixed ones we normally 
assign them.

We had to reconfigure all of our switches from a laptop with a serial 
cable which took AGES.

After some further investigation it seems that the problems we and many 
other people on this list suffer from are caused by the "forward delay" 
setting used in the spanning-tree protocol.

Most implementations of spanning-tree render the port effectively 
unusable for 15 seconds while "port discovery" is performed. Most 
implementations also seem to use a 2 second "initial hello" setting too.

When the udhcp client in busybox tries to get a lease the client simply 
times out because of the "port discovery delay". As mentioned in 
previous posts the busybox dhcp client does not support a length of time 
to wait before failing.

After looking at the code in /packages/base/etc/init.d/network it seems 
that TS makes two attempts to get a dhcp address, this is also mentioned 
by other users on the list.

I decided to put a 20 second delay between the command to bring the 
interface up and the command to request a dhcp lease as follows:

excerpt from /packages/base/etc/init.d/network (approx line 206)
---- snip ----

ifconfig $device up

sleep 20

wireless_config

---- snip ----

This works flawlessly for me now and I can reproduce the problem and fix 
the problems at will. For any of you who would like to try this yourself 
you can test this by either turning spanning tree on and off on your 
switches or changing the "forward delay" setting on a particular port 
(the setting is also known as FDELAY, FAST-PORT or PORT-FAST depending 
on the switch manufacturer)


I would like to suggest the following fix for ts 2.2 final:

A variable called NET_DHCP_DELAY that is set to a value of "0" seconds 
by default but can be overridden using a "NET_DHCP_DELAY=" option in 
thinstation.conf.buildtime (this can not be done in the normal config 
files because you need a working IP Address to be able to retrieve them)

We then only need to add a single line which reads:

Sleep $NET_DHCP_DELAY

This additional line in the existing network script has no knock-on 
effects on any other part of the distribution.

I have tested this and it does not break anything (we simply add a zero 
second delay that can be increased to x number of seconds if required).

Please could this be included in 2.2 final.

Thanks
Jason Meers

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Kanwar Ranbir Sandhu
Linux 2.6.17-1.2141_FC4 i686 GNU/Linux 
10:17:53 up 3:47, 2 users, load average: 0.26, 0.17, 0.18