cross over cable for switch to hub? and router to server?

mitchtin

Hi,

I knew that you should use a straight through cable for host to switch, switch to router, and host to router. plus a rolled cable for console access to network devices. However I recently encountered an exam practice question that asked when a cross over cable should be used, two of the three correct answers were:

when connecting a switch to a hub

when connecting a router to a server



the switch to hub i can understand as i guess they're are kind of the same, although not really. but a router to a server? surely these are not like devices?

Can anyone give a bit of an explanation as to why these answers are correct? That would be greatly appreciated. Thanks

Priston

Routers and PCs are a like in the since that they both use MDI interfaces.

https://en.wikipedia.org/wiki/Medium-dependent_interface

MDI: Routers, PCs, Servers
MDI-X: Switches, Hubs

MDI to MDI: needs crossover.
MDI to MDI-X: needs straight through.
MDI-X to MDI-X: needs crossover.

Auto MDI-X to Auto MDI-X: both crossover and straight through work.

Edit: So host to router would NOT be straight through.

theodoxa

A router and a PC/Server are like devices. In fact, at one time routers ("gateways", "intermediate systems") were essentially just servers.

From the mid-1970s and in the 1980s, general-purpose mini-computers served as routers. Modern high-speed routers are highly specialized computers with extra hardware added to speed both common routing functions, such as packet forwarding, and specialised functions such as IPsec encryption.

There is substantial use of Linux and Unix software based machines, running open source routing code, for research and other applications. Cisco's operating system was independently designed. Major router operating systems, such as those from Juniper Networks and Extreme Networks, are extensively modified versions of Unix software.

https://en.wikipedia.org/wiki/Router_%28computing%29

You can still technically use a a PC as a router. Windows Server has "Routing & Remote Access", which allows it to function as a Router or VPN (PPTP, L2TP, SSTP) Concentrator. If I remember correctly, it even supports OSPF and RIP. There are Linux Distros that can turn a PC into a router also.

clarson

like devices need cross over and unlike devices don't (a straight through). Such as, a pc uses a straight through cable to connect to a switch. Same with a hub, pc uses a straight through cable. So, I'm saying switches and hubs are like devices for this situation. So, connecting a switch and a hub would need a crossover. Similarly, a server uses a straight through cable to connect to a switch. Same with a router or pc. So, for this, a server, a router, and a pc are like devices. So, to connect one to any of the others require a cross over cable.
Of course, the industry has moved away from crossover cables by making switches with auto-mdix. With this, everything connects to a switch using a straight through cable, even other switch like devices.

mitchtin

so to clarify:

a switch to hub connection requires a crossover?

a server to router connection requires a crossover?

a pc to router connection requires a crossover?

Priston

Yes, yes, yes.

popquizkid95

Here's a nice little tip that helps me remember:

Group 1: Router, Host, Server
Group 2: Hub, Switch
If you are connection one device in Group 1 to one device in Group 2: use straight-through cable. i.e Router to Hub or Switch

Two devices in the same group: use crossover cable. i.e
Router to Router
Switch to Switch
PC to PC

james43026

I think what would really help you understand this. Would be if you looked into MDI, MDI-X, auto MDI-X, and DCE vs DTE.