Confusion on which devices need crossover Vs straight-through cable

[JockVSJock]

So Chp 3 has a table that shows devices that use a crossover cable:

Transmit on 1,2 and receives on 3,6
-pc nic
-router
-wireless ap
-network printer

Transmits on 3,6 and receives on 1,2
-hub
-switch

There is a "Do I Already Know This Question" that ask: "There are two devices, which require a straight-through cable?"

The answers are:
-pc and router
-router and hub
-and wireless access point

This question is confusing me because it seems to go against the table above. Plus, on my home network, I have straight-through cable for my dumb switch and AP and they work fine.

The only time I have used crossover cable is when I wanted to connect two pcs together via their nics.

[alan2308]

So Chp 3 has a table that shows devices that use a crossover cable:

Transmit on 1,2 and receives on 3,6
-pc nic
-router
-wireless ap
-network printer

Transmits on 3,6 and receives on 1,2
-hub
-switch

There is a "Do I Already Know This Question" that ask: "There are two devices, which require a straight-through cable?"

The answers are:
-pc and router
-router and hub
-and wireless access point

This question is confusing me because it seems to go against the table above. Plus, on my home network, I have straight-through cable for my dumb switch and AP and they work fine.

The only time I have used crossover cable is when I wanted to connect two pcs together via their nics.

MDI devices (PC's, routers, AP, etc) transmit on 1&2 and receive on 3&6 and MDIX devices (switches and hubs) transmit on 3&6 and receive on 1&2. If you connect two like devices (MDI to MDI or MDIX to MDIX) you use a crossover cable. If you connect two unlike devices (MDI to MDIX) you use a straight through cable. So in your example, you should use a straight through cable when connecting a router to a switch. In the third option you left out the second device, so I can't say there.

The reason that you can get away with using straight through cables on your home network is because a lot of newer Ethernet equipment (and almost all home gear) has what is known as "Ethernet MDI/MDIX Auto Cross" or some similar term which basically means the piece of gear auto senses what it is plugged into and adjusts which pairs it transmit and receives on automagically. Even my ancient Xterasys 802.11b home router can do this. But try connecting two Cisco 2950's together with a straight through cable. It won't work. Connect two 2960's together with the same straight through cable and it will work.

[JockVSJock]

Thanks for the reply.

Hmmm...mdi and mdix. Neither one of these terms are in either Cisco books.

From CTRLink Glossary on Industrial Ethernet Terms

mdi

MDI
Medium Dependent Interface. The name for the connector used to make a physical and electrical connection between a transceiver and a media segment. For example, the RJ-45-style connector is the MDI for 10BASE-T and 100BASE-TX.

mdix

MDI-X
An MDI port on a hub or media converter that implements an internal crossover function. This means that a "straight-through" patch cable can be used to connect a station to this port, since the required signal crossover is performed inside the port instead of in the cable.

[alan2308]

Thanks for the reply.

Hmmm...mdi and mdix. Neither one of these terms are in either Cisco books.

From CTRLink Glossary on Industrial Ethernet Terms

mdi


mdix

I don't remember if those terms are in the CCNA material or not. It's just a lot easier to use MDI than typing "device that transmits on pin 1&2 and receives on pin 3&6" over and over.

[JockVSJock]

Ok, I need to go thru and take notes on the Lammle book. Chp 1 breaks down the following for straight-Through Vs crossover cable:

Straight-Through
-host to switch or hub
-router to switch or hub

Crossover Cable
-switch to switch
-hub to hub
-host to host
-hub to switch
-router direct to host

So now I have another question, if your connection a crossover cable to hub to hub, it needs to go into the uplink port/interface, correct? I reason I ask is that I've never worked with any of this equipment in the enterprise.

[Meast]

Ok, I need to go thru and take notes on the Lammle book. Chp 1 breaks down the following for straight-Through Vs crossover cable:

Straight-Through
-host to switch or hub
-router to switch or hub

Crossover Cable
-switch to switch
-hub to hub
-host to host
-hub to switch
-router direct to host

So now I have another question, if your connection a crossover cable to hub to hub, it needs to go into the uplink port/interface, correct? I reason I ask is that I've never worked with any of this equipment in the enterprise.

Lammle explains it the best in my opinion, I'm reading the same book, I'm on chapter 4!

[Project2501]

L3 to L3 = cross
L2 to L3 = straight
L2 to L2 = cross