Re: DHCP timeout is too short for this college network

[José Queiroz <zekkerj gmail com>]

Hi Daniel,

NM needs a lot of fixes and improvements, but I think that in this
case, it is completely innocent.

Your dhcp server is too lazy, as you can see: it only answered for the
initial DHCPDISCOVER on the third attempt, the same for the other
messages of the DHCP sequence.

Maybe you should ask for the support team to analyze the traffic
exchanged between your station and the dhcp server, to understand why
the messages are being lost.

2010/1/11 Daniel Gnoutcheff <daniel gnoutcheff name>:
> Hello all,
>
> First off, let me take this opportunity to thank you all for this really
> cool piece of software. Networking with n-m is great fun. :)
>
> OK, the problem I'm having is a college campus network that has really slow
> DHCP severs. As in, up to 3 *minutes* to get a lease. Here's a typical
> dhclient run, with timestamps:
>
>> Jan 10 21:38:26 Listening on LPF/eth0/00:15:58:c6:29:b6
>> Jan 10 21:38:26 Sending on   LPF/eth0/00:15:58:c6:29:b6
>> Jan 10 21:38:26 Sending on   Socket/fallback
>> Jan 10 21:38:30 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 8
>> Jan 10 21:38:38 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval
>> 12
>> Jan 10 21:38:50 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval
>> 20
>> Jan 10 21:38:50 DHCPOFFER of 149.106.215.247 from 149.106.192.253
>> Jan 10 21:38:50 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:38:54 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:39:02 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 4
>> Jan 10 21:39:06 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 9
>> Jan 10 21:39:15 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval
>> 12
>> Jan 10 21:39:21 DHCPOFFER of 149.106.215.247 from 149.106.192.253
>> Jan 10 21:39:21 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:39:25 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:39:32 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 7
>> Jan 10 21:39:39 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval
>> 14
>> Jan 10 21:39:53 DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval
>> 18
>> Jan 10 21:40:02 DHCPOFFER of 149.106.215.247 from 149.106.192.253
>> Jan 10 21:40:02 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:40:08 DHCPREQUEST of 149.106.215.247 on eth0 to 255.255.255.255
>> port 67
>> Jan 10 21:40:12 DHCPACK of 149.106.215.247 from 149.106.192.253
>> Jan 10 21:40:13 bound to 149.106.215.247 -- renewal in 286274 seconds.
>
> As you can see, dhclient does have the patience needed to drag a lease out
> of these servers. But it took over 100 seconds and thus would have been
> prematurely killed by n-m. Thus, I usually have to manually tell n-m to
> retry, multiple times. This often gets quite annoying, and on bad days I
> often end up killing n-m and using dhclient manually.
>
> It's worth mentioning that the resident IT department has acknowledged the
> problem. Sadly, it also seems like they aren't going to do anything about it
> anytime soon, presumably because Windows and MacOS tolerate the slowness. So
> in the meantime, it'd be great to get n-m to work with networks like these
> -- and I volunteer to help! (This would be my first time contributing to a
> software project, so it might take me a while, but I'll give it my best
> shot.)
>
> dhclient has its own set of timeouts, which seem to be setup quite
> intelligently. So it seems to me that, from the perspective of my network at
> least, we would do well to let dhclient decide when DHCP is hopeless. Is
> there anything getting in the way that? Is the link-local thing going to be
> a problem?
>
> Have a good one,
> Daniel
>
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