straight cable used as trunk line???

itdaddy

Hey ccnp gurus,

we had a vendor come into our work and setup up a fiber line 10meg.
okay to a fiber patch panel and then the fiber 1 pair to the 2950 switch
on a fiber port. then we are using port 1 of 2950 Lan port as a trunk to
the Gateway router.(has csu/dsu built into interface) okay.

for a trunk like to the gateway from the 2950 switch you can use a straight cable as a trunk line? I always thought you coudl only use
a cross-over cable for trunks froms switches to routers. why is this possible can anyone explain this. Thanks

dynamik

I don't think the type of cable is dependent on trunks. You use cross-over cables between like devices, such as between hubs and switches or between routers and PC, and you use straight-through cables for dissimilar devices. Since routers and switches are different types of devices, you should be set with a straight-through cable.

redwarrior

Traditionally, you used a straight-through cable for connections between un-like devices (PC to switch, switch to router, etc) and a cross-over for connections between like devices regardless of the port type (switch to switch, PC to router, etc). Now, though, most new switches auto-sense when they need to crossover and handle it for you, which is really handy when you don't have a crossover cable. (You can still use one with these, but it's not necessary anymore.)

Hope this helps!

Netwurk

redwarrior wrote: »

Traditionally, you used a straight-through cable for connections between un-like devices (PC to switch, switch to router, etc) and a cross-over for connections between like devices regardless of the port type (switch to switch, PC to router, etc). Now, though, most new switches auto-sense when they need to crossover and handle it for you, which is really handy when you don't have a crossover cable. (You can still use one with these, but it's not necessary anymore.)

Hope this helps!

Not necessarily true. For example, the somewhat modern 3550 does not support auto-MDIX.

To find out whether on not your switch does, try running the transceiver command on it

For example:

Sw3550#show interfaces transceiver properties | include MDIX
Administrative Auto-MDIX: N/A
Operational Auto-MDIX: N/A

There are also some switches that support auto-MDIX, but only in auto-sense mode. So they work when duplex is set to auto, but they'll fail if you set it manually to half or full duplex.

billyr

Assuming a device does not support auto-mdix, I always keep the following in mind.

If a device shares the same layer of the OSI model or there are 2 layers of difference between them; then use a cross over cable.

If there is one layer of difference between them then use a straight through cable.

Layer 3: Router
Layer 2: Switch
Layer 1: P.C, Hub, Repeater.

Router to Router = Same layer = Cross over.
Switch to Router = 1 layer = Straight through.
P.C to Router = 2 Layers = Cross over.

itdaddy

yeah, I have always known like devices get the crossover (pc to router, or router outer, switch to switch) For some reason I was stuck on trunking from router (like ROS to swith) and needing a crosover for some reason..huh brain fart! hah

Thanks for all the great explanations..wow great help. I do not have access to great engineers like you guys. thanks what a great forum this is. I just for some reason got stuck on trunks being cross-over for some reason..thanks alot! but then again on our Poe switches we have trunks for all our IP phones hum! just putting it all together. thank you guys!