How to get the best out of a Switch

[Arne Krag-Andersen]

We have redesigned a lecture room, with only two LAN connections in the room besides WLAN connections.

It is now going to be a computer training room, and for the time being it is completely impossible to have the room cabled completely.

We decided to use a switch to connect the computers, but the broadband speed dropped by 80% immediately. We have tested swith a cheap hub, and it gave a normal speed, which is contrary to what we would have thought.

As you might appreciate, switch technology is not our main field, and we are in a fix. It will probably be solved in two-three weeks, and we realise that our redesigning was slightly premature, but there is no turning back now. The room, which has been dearly needed is already in use.

Aftet this long preamble our question is very short; Asssuming that our Switch, when it was used for normal direction of cables to the router, functioned completely normally, what do we do wrong?

To make an answer a little easier, I will try to describe briefly what we have done:

1) We have connected the switch to the wall with a normal cable.

2) We have connected the socket (is that the proper term?) in the patch panel to the router with a crossed cable

3) We have connected a hub to one of the contacts in the Switch with a normal cable

4) 13 contacts are used for 13 machines with normal cables

5) 7 machines are connected to the hub with normal cables.

The seven last machines have a speed which is app. 250% of those 13 connected to the switch.

Can anyone help us?

[Anders_35]

Arne,

speed problems with switches are often related to auto-negotiation of link speed.

You say nothing about what speeds you are running at. 10/100/1000 ?

Check your switch for a errors on "collisions", "problem cables",
"speed/duplex mismatch" or similar.

Try setting all network cards and/or switch ports to fixed speed settings.
(or just try one port first, and see what happens...)

Even if the card and switch port both report that they are operating at the same speed, they might not do so.

[Les Ligetfalvy]

More often than not, it is duplex and not speed that gets misconfigured. The hub would most likey have negotiated half duplex. Uplinks should always be fixed and never left to auto.

[wong seng guan]

Hi Arne,

you made a mistake on your action No 2 and 3. because you have to use straight cable to connect switch to router and cross cable for hub to switch.

i think should be no problem if you follow the way i teach u

thank

[Les Ligetfalvy]

I have to disagree with wong. Switches are normally connected to routers with crossover cables but most modern switches are Auto-MDIX anyway. If the wrong cable were used, you would have no traffic flowing at all.

Just as I stated in my prior post, uplinks should never be left to chance and should always be fixed. This includes MDI/MDIX.