Re: isc-dhcp-server not receiving DHCPDISCOVER
On 12/05/2013 06:04 PM, Bob Proulx wrote:
> Russell L. Carter wrote:
>> Ok, I need to do some experimenting here. I've broken out a long patch
>> cable to bypass the switch
>
> I would really be surprised if the switch has broken down. Not impossible
> of course. But what are the odds? I think it very unlikely. If I were to
> guess I would guess it more likely that packets are being routed to the
> wrong place. I think that is many times more likely.
>
>> and am steeling myself for the tcpdump learning experience.
>
> You will be surprised how easy it is! Just run it. Control-C out of it to
> stop it.
>
So the awesome foodie in-laws dropped in for a couple of days, and I'm
the cook. But I shooed them off this morning and finally got a chance
to look at this again. I reconfigured my net to get the DHCP
conversation on the least used net, patched the laptop directly to the
server, and on the server ran
$ tcpdump -lenx -i eth1 -s 1500 port bootps or port bootpc
On the laptop I generally use wicd, and I know that works, so to
simplify things I just told wicd to connect using DHCP.
And it worked! I'd not have such a shiny head today if I had done
this months ago, when I first noticed the weirdness. I just used the
DD-WRT AP DHCP server so that I could maximize my procrastination
metrics.
So then the problem was to figure what was awry with the switch, a
D-Link DGS-1224T. I thought I had sometime in the distant past
lobotomized it but it turns out no, I didn't get it done completely.
In particular, IGMP snooping was enabled. I downloaded the switch's
manual (thanks D-Link!) and here is what it said:
"With Internet Group Management Protocol (IGMP) snooping, the
Web-Smart Switch can make intelligent multicast forwarding decisions
by examining the contents of each frame’s Layer 2 MAC header. IGMP
snooping can help reduce cluttered traffic on the LAN. With IGMP
snooping enabled globally, the Web-Smart Switch will forward
multicast traffic only to connections that have group members
attached."
But there were no "group members" defined. Oops. Disabled, applied,
power off/on, voilà.
Thanks Bob!
(I used this tutorial for tcpdump:
http://www.danielmiessler.com/study/tcpdump/
I guess I'm a believer now.)
> Good luck!
>
> Bob
>
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