need some networking help!

Tue May 11 23:37:13 UTC 2010

On Tue, May 11, 2010 at 5:02 PM, Thomas Milne
<tbrucemilne-TcoXwbchSccMMYnvST3LeUB+6BGkLq7r at public.gmane.org> wrote:
> On Tue, May 11, 2010 at 3:41 PM, Jamon Camisso
> <jamon.camisso-H217xnMUJC0sA/PxXw9srA at public.gmane.org> wrote:
>> On 05/11/2010 12:00 PM, Matt Price wrote:
>>> Hey folks,
>>>
>>> I'm hoping there's someone out there who can help me with a networking
>>> problem; I kind of doubt the issue is linux-based byt i suppose it's
>>> possible.
>>>
>>> Here's the deal:  I am building an ubuntu-based computer centre in the
>>> basement of a social housing building in Kensington Market.  The
>>> internet here comesi n via dsl to an 8-port router and is farmed out
>>> from there to various computers and I believe a wireless outer
>>> somewhere else in the building. I was hoping to connect a donated hub
>>> (thanks PlanetGeek!) to the router and use the hub to serve out
>>> internet service to the computers in our little cluster,but try as i
>>> might I can't get a dhcp connection to work.
>>>
>>> here's a little more info:
>>>
>>> the hub is a D-link DES-1024R 10/100 switch. there's no serial console
>>> & nothing in the manual about setting the switch up.
>>> (manual is here:http://www.google.com/url?sa=t&source=web&ct=res&cd=1&ved=0CBIQFjAA&url=ftp%3A%2F%2Fftp.dlink.co.uk%2Fswitches%2Fdes-1016r%2Fdes-1016r_manual_v.02.pdf&ei=V33pS8ytDIP68Aahw9TmDg&usg=AFQjCNG9XxOyyCFBtkqn7JP5wZnVJJtFqA&sig2=EE4ha-MwDs8kkOZCU_Ep6g)
>>>
>>> Attaching a straight-through cat-5 cable from the router to either the
>>> uplink or one of the standard ports, I get solid green on both lights
>>> for that port, indicating an active link.
>>> attaching another cable from one of the other ports to my laptop, i
>>> get two more green lights on that port, again indicating an active
>>> link.
>>>
>>> unfortunately, network-manager fails to connect (this is under ubuntu
>>> lucid, so a recent n-m).
>>>
>>> the same cables work fine for me if i hook my laptop directly into the
>>> hub, so i know that's not the issue.
>>>
>>> logs indicate that i'm getting a dhcp timeout; i've attached a sample
>>> output from /var/log/daemon.log so you cna see what I mean.
>>>
>>> Anyway, if anyone can help i'd be really grateful.  This is a
>>> volunteer project, too -- if you feel like volunteering some time --
>>> or if you think my switch is broken & you havea  better one -- by all
>>> means let me know!  thanks much,
>>
>> Not sure I understand the topology you're describing. In one place you
>> refer to an 8 port router, another hub, and another switch. Technically
>> those are 3 separate pieces of hardware. However, the 8 port router
>> likely combines switch+hub for you so I think your network looks like this?
>>
>>         |
>>       DSL In
>>         |
>>         |
>>   8 port router
>>         |
>>        / \
>>       /   \
>>     WiFi   |
>>            |
>>        DES-1024R
>>
>> So, my suggestion would be to first figure out where clients that do get
>> a DHCP address are receiving it from. Put tcpdump or Wireshark to work
>> on a system that is attached to each of the router/wifi/switch to see
>> how the traffic flows through and is broadcast on the network.
>>
>> Also, to test the functionality of the DES-1024R itself, disconnect it
>> from the uplink and run a DHCP server of your laptop etc. and see if
>> another system on one of the switch's ports receives an IP (again, use
>> Wireshark to capture the traffic).
>>
>> Just some things to try, good luck!
>>
>
> I'm pretty sure what he's saying is that he has a hub/switch between
> the router and clients. Nevertheless your advice is accurate, and it
> is confusing to me when he says that "the same cables work fine for me
> if i hook my laptop directly into the
> hub, so i know that's not the issue.". Does that mean he gets
> connected to the 'Net? and without any interaction with the router?
> That makes no sense to me, but it's been awhile, so...

hey folks,

stupidly switched my tlug mail to gmail and so am not sure i'm
replying to the right subthread, but:  apologies to esp. jamon and
thomas for the confused terminology.  I meant to say "the same cables
work fine for me if i hook my laptop directly into the ROUTER" -- as
usual i was typing in a hurry, this time bc i was being kicked out of
the basement over at the site.  The word "hub" shouldn't have been
used at all

the topology is (forgive non-monospaced diagram):

   DSL
      |
ROUTER
   |    \        \
   |     \         \
   |       \        Other Stuff
   |          \
802.11     My Switch
                   |
                   |
               Ubuntu Desktops/My Test Laptop

The router provides dhcp to everyone else, including (I think) the
802.11 wireless service, which I shouldn't have mentioned anyway since
it has no bearing on this problem.   if i bypass the switch by hooking
in directly to the router I can connect directly to the 'Net, no
problem.  However, the DHCP client on my laptop fails to connect if I
wire things as shown above.

My main question is, at what point should I consider the problem to be
an issue with the switch?  If the uplink port has an issue, shouldn't
I just be able to plug the router into one of the other switch ports?
I thought most switches would sort of automagically route traffic to
the outgoing port.

anyway thanks to both of you; Jamon, I will try wireshark & tcpdump
when I get back to the site on thursday.  best,
matt
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