Can't figure out what type of cables needed!

SurferdudeHB

I'm confused between when to use straight through, cross over and roll over cable. How did you guys remember which type of cable to use in connecting devices?

hodgey87

It does take a while, but once your labbing all the time it becomes second nature. Main ones are:

PC - Switch = Straight through
Switch - Router = Straight through
PC - Router = Crossover

trackit

straight through: all wires in the cable go straight through (logically speaking) rx on one end are connected to rx on other end and tx on one end are connected to tx on other end. Use this cable if you are connecting devices that are "meant" to be directly connected together (usually different type of devices ie pc to a switch)

crossover: rx on one end of the cable are crossed over to tx on other end. Use this cable if you are connectong devices that are not "meant" to be directly connected (usually same type of devices ie one pc to another pc).

rollover: this is just a fancy name for ciscos console cable use this if you want to connect a pc to a ciscos device console port.

mikem2te

For network cables I look at the OSI Layer. If the devices are at the same layer then it is a crossover, if they are different layers then it is a straight through.

Routers and computers operate at Layer 3, ie IP aware.
Switches are Layer 2.

So-
Router (L3) to PC (L3) - Crossover
Router (L3) to Switch (L2) - Straight through
Switch (L2) to Switch (L2) - Crossover


OK, there are Layer 3 switches but they are still only Layer 2 devices with many extra bells and whistles.

tigerplug

Like devices = crossover
unlike devices = straight through

console = rollover

rono

A network involves 2 switches and a router all cabled together in a "bus-like" topology.The link between sw1 and sw2 shall be a crossover cable or a straight through cable and configured as a trunk?

SW1 --a-- SW2 --b-- R1 ?

a = crossover or a straight through cable/trunk??
b = straight through cable(this is clear for me )

thanks,

rogue2shadow

rono wrote: »

A network involves 2 switches and a router all cabled together in a "bus-like" topology.The link between sw1 and sw2 shall be a crossover cable or a straight through cable and configured as a trunk?

SW1 --a-- SW2 --b-- R1 ?

a = crossover or a straight through cable/trunk??
b = straight through cable(this is clear for me )

thanks,

A will be a crossover due to both switches being like devices. This was really rough for me during the beginnings of the networking academy. Once you do it enough it in packet tracer or GNS3, it'll get burned into your retinas

xenodamus

tigerplug wrote: »

Like devices = crossover
unlike devices = straight through

To elaborate on that:

Routers, PCs, Access points = Like devices

Switches, Hubs = Like devices

fly351

mikem2te wrote: »

For network cables I look at the OSI Layer. If the devices are at the same layer then it is a crossover, if they are different layers then it is a straight through.

Routers and computers operate at Layer 3, ie IP aware.
Switches are Layer 2.

So-
Router (L3) to PC (L3) - Crossover
Router (L3) to Switch (L2) - Straight through
Switch (L2) to Switch (L2) - Crossover


OK, there are Layer 3 switches but they are still only Layer 2 devices with many extra bells and whistles.

Yep, look at the OSI Layers. Same Layer = cross over. Different layers = straight through.

jojopramos

straight through = PC to switch or hub
Router to switch or hub

crossover = switch to switch, router to router, pc to pc, hub to hub, PC to router, and hub to switch

rollover = console cable

alan2308

fly351 wrote: »

Yep, look at the OSI Layers. Same Layer = cross over. Different layers = straight through.

What about switch to hub?

bubble2005

Straight through cable:

Router ----> Switch or Hub
Pc

---

>Switch or Hub

Rolled Cable for Mgmt purposes and config of switch or router (console)
Router ----> PC
Switch ----> PC

Cross Over Cable
Use for any other combination
Router ----> PC
Router ---->Router
PC ----> PC
Switch ---->Switch
Switch ----> Hub
Hub--->Hub

I make it easier for me by remembering : Router or PC to Switch and Hub ---> Straight through cable.

Heero

I think it is significantly easier to just try and understand WHY you need the different cables.

a device transmits on pin 1&2. This has to be recieved on pin 3&6 on the destination device. A crossover cable crosses the pins so that pins 1&2 end up as pins 3&6 on the other end.

Now here is the tricky thing. Both switches and hubs perform this "crossover" internally. Because of this, you just use a straight through cable and let the switch to the crossover.

And then a rollover cable is ONLY used to connect to the console port of a cisco device. It is NEVER actively used in a networking environment for transmitting traffic.

ccnxjr

I'd first try building a lab with NO store bought patch cables
Clip the ends off and crimp your own ends, you'll get a healthy appreciation of which cable goes where and pay closer attention to the cabling standards (especially if you crimp them wrong!)
There is no substitute for hard work and a few mistakes (other than loads of money)
If you don't have a lab, get some cat 5 cables and rj 45 connectors and just crimp cables for the fun of it.

I may seem like re-stating what's already posted, but maybe if you see the same information in a different form you might understand it better, which helped me study.

There are only so many combos:

Host 2 host =Crossover
Host 2 hub = Straight through
Host 2 switch= Straight through*
Host to router = Crossover

Hub 2 host = Straight Through
Hub 2 Hub (why?)= Crossover
hub 2 switch = Crossover
Hub 2 router = Straight Through

Switch 2 host = Straight Through*
Switch 2 hub = Crossover
Switch 2 switch = Crossover
Switch 2 router = Straight Through

Router 2 host = Crossover *
Router 2 hub = straight through
Router 2 switch = straight through
Router 2 Router = Crossover

*You will only use the rollover cable to connect to the Console port of a Switch or Router

liz p.

thats how i do it.

pairs of devices need a crossover
ie.. a 'pair' of switches, a 'pair' of routers

SW-SW
R-R
SW-HUB
*exception to the 'pair' rule: PC-R

anything else, straight through. or think of it like this: when was the last time you (intentionally) used a crossover to connect a pc to a switch?

also, a console cable is used when console-ing in with hyperterminal (or z-term for mac users i think)

Netwurk

Console cable is called a rollover, pins 1-8 are "rolled over" and connected to pins 8-1

Mark Knutson

mikem2te wrote: »

For network cables I look at the OSI Layer. If the devices are at the same layer then it is a crossover, if they are different layers then it is a straight through.

Routers and computers operate at Layer 3, ie IP aware.
Switches are Layer 2. ...
OK, there are Layer 3 switches but they are still only Layer 2 devices with many extra bells and whistles.

I will keep this in mind. I have an understanding of which devices need what, but not a systematic way to explain it. I was thinking in terms of type a and type b devices.

I am not fully up to speed on layer three switches, but from what I recall of the documentation, you can configure a port to be part of the switch or go straight to the router. So, a port would be designated layer 2 or 3 as desired.

tha_dub

I usually just look at it this way. Almost everything plugs into a switch (except another switch) with a straight through so if it's straight through to a switch then those two devices plugged together need crossover....

Everyone has a different method to remember; use whatever works for you.

spartangtr

alan2308 wrote: »

What about switch to hub?

Get out of here with that, who uses hubs anymore...

fly351

...I say we bring back some 10base5 and vampire taps!!!!

jojopramos

I know that switch to switch should be cross cable, but my question relies on the real world. Why can I connect 2 Cisco catalyst 2960 through straight through cable and it still works. What is the negative impact of connecting the 2 switch via staright through? As for now, our network is fine even I am connected by straigh through on my switches. We have 5 Cisco Catalyst which is connected via straight through and still working great. wierd....

kalebksp

Most modern switches (including 2960s) and NICs support Auto-MDIX which internally swaps the pairs so that it doesn't matter whether you use straight or crossover.

jojopramos

thanks for clarification. I am really confused with this. So now it is known that new switches today use straight through cable on switch to switch connectivity... cheers...

froufrou123

Easy way to remember ... Devices that are alike use crossover and devices that are unlike to each other using straight-through with Router to PC exceptionally using crossover. (hope I'm right)

So, e.g. Switch to Switch (devices alike, use crossover)
Switch to Hub (devices alike, use crossover)
Router to Switch (devices unlike, use straight-through)

mikej412

jojopramos wrote: »

What is the negative impact of connecting the 2 switch via staright through?

Auto-MDIX relies on port negotiation -- so if someone hard codes speed or duplex you could lose Auto-MDIX and the link.

jojopramos

Thanks Mike, so the safest is just to use crosscable because if i will implement some enhanced switching function (etherchannel, speed...) it may disable the auto-MDIX in the connected interface. Thanks.

Heero

use the right cable if you think there is any chance of disabling auto-mdix