This question might be silly

VinUnleaded

So I just got to the router part of my Packet Tracer lab. The lab ask me to enable telnet but then I cannot ping it or telnet into it.

Then I replaced the straight-through cable with a cross-over cable then it started working. I thought we were suppose to connect 2 like devices with cross-over cables? The laptop and Router should not be like devices should they?
Router is 2620XM

alan2308

Nope, not a a silly question at all. All one has to do is take a look at the Wikipedia article to see how confusing this gets made out to be. The PC and router are like devices (regardless of which model router it is).

There are two pinouts on Ethernet ports, MDI and MDI-X. MDI-X pinouts are found on switches, bridges and hubs, MDI are found on pretty much everything else. Like devices means that either both are MDI, or both are MDI-X. Unlike devices means that one is MDI and one is MDI-X.

CodeBlox

Some models allow you to use the wrong cable but flip the pinout logic on one end.

Just know that

Host - Router = Crossover *EDIT - Carelessly said straight through
Host - Switch = straight through
Switch - Switch = Crossover
Switch - Router = Straight through
Router - Router = Crossover

Futura

I used a 1760 Router connected to Laptop and that needed a Crossover to work?

alan2308

CodeBlox wrote: »

Some models allow you to use the wrong cable but flip the pinout logic on one end.

Just know that

Host - Router = straight through
Host - Switch = straight through
Switch - Switch = Crossover
Switch - Router = Straight through
Router - Router = Crossover

I would prefer to learn how it works than trying to just memorize a list. That way you would know that pc to router is a crossover, not a straight through.

And don't forget about uplink ports which don't fit "Switch - Switch = Crossover."

Futura

Might I also add that I have a 800 series router but that is also a switch with 4 switch ports!!!

This was a good article for me!

Links to this BBS

http://www.techexams.net/forums/ccna-ccent/37574-query-about-cross-over-straight-through-cable.html

Priston

CodeBlox wrote: »

Host - Router = straight through

Host - Router = Crossover

CodeBlox

alan2308 wrote: »

I would prefer to learn how it works than trying to just memorize a list. That way you would know that pc to router is a crossover, not a straight through.

And don't forget about uplink ports which don't fit "Switch - Switch = Crossover."

Hahaha whoops, I knew that! Really I did! And I didn't memorize that either. I know that Host AND routers transmit on pins 1 and 2 and recieve on 3 and 6. I'm just so nervous about taking my ICND1 in about an hour and half.

I'll go edit that.

f3z81

CodeBlox wrote: »

Some models allow you to use the wrong cable but flip the pinout logic on one end.

Just know that

Host - Router = Crossover *EDIT - Carelessly said straight through
Host - Switch = straight through
Switch - Switch = Crossover
Switch - Router = Straight through
Router - Router = Crossover

The way I remember it is a switch is layer 2 and a PC/Rouer are Layer 3

If its like to like devices ie L3 to L3 or L2 to L2 its crossover cable

and if its not like to like

L2 to L3 or L3 to L2 its a straight through.

alan2308

f3z81 wrote: »

The way I remember it is a switch is layer 2 and a PC/Rouer are Layer 3

If its like to like devices ie L3 to L3 or L2 to L2 its crossover cable

and if its not like to like

L2 to L3 or L3 to L2 its a straight through.

A wireless AP is layer 2. A switch is layer 2. How do they connect?

I'll say it again. It's better to learn how things actually work than memorizing lists.

CodeBlox

And when you say "know how it actually works" what do you mean in this context?

alan2308

CodeBlox wrote: »

And when you say "know how it actually works" what do you mean in this context?

I mean (in this case) knowing the difference between MDI and MDIX, understanding the purpose of each (as in why a switch/bridge/hub utilized MDIX) and not just trying to remember "host to router = crossover," "host to switch = straight-through," etc. Lists such as that, or generalizations such as the one f3z81 made will always have an exception or two.

MDI and MDIX may not actually appear on an exam, but their function has a great effect on things that will appear on the exam.

CodeBlox

Hmm, this may sound weird but it turns out I knew what (Auto-)MDI(X) was. I even mentioned the auto correcting cable mis-match in my earlier post. Just didn't know it was called auto-mdix. I guess it was rather foolish though to post that list and suggest someone memorize it. I agree though, it's better to know how things work. Like learning the binary math involved in subnetting. I use a much quicker method to subnet, but it's a sure-fire way to verify correctness.

hasitha257

VinUnleaded , remember nothing is ever silly.

Here's how I learned things when I started my networking days


Hub - Layer 1 of OSI model
Switch - Layer 2 of OSI model
Router - Layer 3 of OSI model
PC - Layer 3 of OSI model


When you are connecting devices in different layer of OSI model use straight through.

When you are connecting devices in same layer of OSI model use a Cross over cable.

hasitha257

alan2308 wrote: »

Nope, not a a silly question at all. All one has to do is take a look at the Wikipedia article to see how confusing this gets made out to be. The PC and router are like devices (regardless of which model router it is).

There are two pinouts on Ethernet ports, MDI and MDI-X. MDI-X pinouts are found on switches, bridges and hubs, MDI are found on pretty much everything else. Like devices means that either both are MDI, or both are MDI-X. Unlike devices means that one is MDI and one is MDI-X.

Auto MDI-X feature enables the port to automatically detect and adapt based upon the Cable type ( i.e either Straight or X-over cable) so users shouldn't worry about debating cable type to use ......

CodeBlox

hasitha257 wrote: »

Auto MDI-X feature enables the port to automatically detect and adapt based upon the Cable type ( i.e either Straight or X-over cable) so users shouldn't worry about debating cable type to use ......

But I don't think that flies with some older hardware.

f3z81

alan2308 wrote: »

I mean (in this case) knowing the difference between MDI and MDIX, understanding the purpose of each (as in why a switch/bridge/hub utilized MDIX) and not just trying to remember "host to router = crossover," "host to switch = straight-through," etc. Lists such as that, or generalizations such as the one f3z81 made will always have an exception or two.

MDI and MDIX may not actually appear on an exam, but their function has a great effect on things that will appear on the exam.

I am currently studding for my CCNA, and MDI and MDIX is covered in the CCNA 1 exploration course, my understanding of it was exactly what you had in your first post.

From what I remember LAN devices typical use MDIX i.e. hubs switches and they do the crossover internally so as to make connection to an end device easier in terms of cabling.

As I am only about a third of the way through the CCNA course I have not yet covered anything that would be an exception to the rule.


With regards to your example of the access point, I take it; you would connect it via a straight through cable rather than a crossover cable? Or is an access point one of these device that can flip the MDI / MDI-X connection itself, so it can work with both?

I do still like my L2 and L3 examples as it helps me understand and also explains why a PC and router both are classed as like devices (Both at use Layer 3 of the OSI model and deal with IP address etc).

f3z81

hasitha257 wrote: »

VinUnleaded , remember nothing is ever silly.

Here's how I learned things when I started my networking days


Hub - Layer 1 of OSI model
Switch - Layer 2 of OSI model
Router - Layer 3 of OSI model
PC - Layer 3 of OSI model


When you are connecting devices in different layer of OSI model use straight through.

When you are connecting devices in same layer of OSI model use a Cross over cable.

This was my take on things. EDIT: although I would say connecting a hub to a switch would have to be one of these exceptions to the rule as, a switch to a hub would be connected via a crossover cable.

hasitha257

f3z81 wrote: »

This was my take on things. EDIT: although I would say connecting a hub to a switch would have to be one of these exceptions to the rule as, a switch to a hub would be connected via a crossover cable.

Did we go to same school ? college? just kidding , I didn't read you post sorry......

f3z81

hasitha257 wrote: »

Did we go to same school ? college? just kidding , I didn't read you post sorry......

No worries mate, just glad I am not the only one that thought of it like that. lol