Problem with wired network - switch needs a hub ??

  pjlewis 23:58 21 Jun 2006
Locked

Hi,
I work with a charity and by default am responsible for the network. I am self-discovered (note - not taught) and this latest one has me completely baffled.
We have broadband coming into the building via a Vigor2800 router. This then goes into 2 dynamode switches and out to various offices.
We have just started playing with asterisk and IP phones. So one office has a line coming from the dynamode switch (these are straight leads with a socket on the wall). If I plug the IP phone (a grandstream gxp2000) directly into the socket, the phone doesn't seem to connect with the router and therefore doesn't get an IP address. However, if I plug a simple hub into the socket first, and plug the IP phone into that - no probs, IP address straight away.
Anyone any ideas why this should happen ??

To give another example of where I'm at ...
Again, an office has a socket on the wall, this time there are two computers in the office so I need a switch/hub to split the network. If I put a switch in, again no IP address. If I use a hub - no probs at all.

Am I missing something in my understanding of how switches and hubs work / interact ?

I am baffled - HELP !!

Thank

Pete

  mgmcc 08:20 22 Jun 2006

I *SUSPECT* the problems are down to "crossover" versus "straight wired" cables when daisy-chaining switches. Often switches have an "Uplink" port (or one that can be toggled between LAN and Uplink) the effect of which is the same as using a crossover cable. Do the hubs you are using have a port dedicated to the link back to the feed, as this will be "crossover"?

  pjlewis 12:10 22 Jun 2006

Hi,
Thanks for the reply. Some of the hubs I am using have uplink ports, which I am using. However, the main switch and the router don't have uplink ports, so I presumed they were autosensing ???
Pete

  mgmcc 12:43 22 Jun 2006

<<< I presumed they were autosensing >>>

I think you are going to have to try a crossover cable (or crossover adapter if you can find one) to see if that eliminates the problem.

  pjlewis 23:35 22 Jun 2006

Hi,
Where would I put the crossover cable ? Between the router and the first switch ? Why would putting a hub on the end of the line make a difference if I had the wrong cable between the router and first switch ?
Pete

  mgmcc 23:58 22 Jun 2006

<<< Where would I put the crossover cable ? >>>

You said previously:
"Again, an office has a socket on the wall, this time there are two computers in the office so I need a switch/hub to split the network. If I put a switch in, again no IP address. If I use a hub - no probs at all."

So try a crossover cable between the socket on the wall and the "switch" which, with a straight cable, doesn't let the two computers connected to it get their IP addresses. Then see if they do get IP addresses when the crossover cable is used.

  pjlewis 07:10 23 Jun 2006

Hi,
Thanks will give it a go. Any ideas on the first of my examples - ie. the IP phone not working when connected straight (if indirectly) to the switch, but working when connected via a hub ?
Pete

  mgmcc 08:00 23 Jun 2006

<<< Any ideas on the first of my examples - ie. the IP phone not working when connected straight (if indirectly) to the switch >>>

Basically the same test. Connect the phone to the switch again after you have inserted the crossover cable between the wall socket and the switch. This "crossover" of connections between wall and switch, if that was the problem, will have corrected all connections from that point on.

  pjlewis 08:19 23 Jun 2006

Hi,

No the problem with the phone is the other way around. If I connect the phone directly into the wall socket then I can't get an IP address, if I connect a hub to the switch first (using the uplink port on the hub and a non-crossover cable) , then the phone picks up an IP address no probs.
Pete

  pjlewis 11:37 24 Jun 2006

Hi,
Phoned up dynamode yesterday and they confirmed that if I was connecting another switch to one of their switches, then I should use a crossover cable and not a straight patch lead. With the phone, again I looked further at the specs for the phone. Basically there is a connection on the back for you to 'piggy back' a pc on to it - I'm guessing that this makes it a mini 2 port switch, and so it would need a crossover cable connecting it to the wall port and not a patch cable.
I know that 'modern' switches have the capability to autosense whether a straight patch or crossover is being connected and make adjustments itself. I'd seen switches with an uplink port and those without and presumed that those without are 'autosensing'. This seems to be an inaccurate presumption.

Thanks for your help, I have ordered some crossover cables and will try them on mon/tue and see what happens.

Pete

  pjlewis 16:40 08 Jul 2006

Hi,

Well, I am now totally baffled. I'd convinced myself that using crossover cables would solve all this - but no !!

Got some crossover cables from ebuyer, and tested it on the IP phone.

As per the postings above, the situation was that if I plug the phone (using a straight through patch cable) into the wall socket, it cannot get an IP address. However, if I go via a hub - ie. using a straight through cable to connect the hub via an uplink port on the hub, then use another straight through cable to plug the phone into the hub - then no probs, IP address in seconds.

Well I tried using one of the new (I've actually tried 2 of them just to make sure it wasn't a dodgy cable) crossover cables and - no difference. Still no IP address plugging in straight to the wall.....

I am baffled ! Anyone got any other ideas ??

Pete

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