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When I studied for the CCNA, I learned which devices should be connected using a straight through cable and which using a crossover cable. For example take this explanation for question one from a study site.

Group 1: Router, Host(PC), Server

Group 2: Hub, Switch

One device in group 1 + One device in group 2: use straight-through cable

Two devices in the same group: use crossover cable

Based on this I should use a crossover cable between a router and PC.

But, I have an Internet connection with a DSL router. In this scenario I'm using a straight through cable between my router and PC.

So this has me confused, why can I use a straight through cable between my DSL router and PC?

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migrated from networkengineering.stackexchange.com Jul 25 at 1:53

This question came from our site for network engineers.

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Most "routers" have both incoming (from the outside network) and outgoing (to local devices) connections. The latter are just like hub/switch ports. –  Daniel R Hicks Jul 25 at 3:07

3 Answers 3

up vote 6 down vote accepted

Two reasons:

  • Your DSL router probably has an integrated (usually 4 port) switch (those 4 lan ports on the back side)
  • Most modern network cards support Auto MDI-X, so they can 'swap' the pin assignment (so you can use the "wrong" cable)
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i.e it's DSL modem-switch not a DSL modem-router –  Trojan Jul 24 at 18:05
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It's a router because of its L3 functionality. It just has an internal switch in the unit for additional connectivity. –  David Houde Jul 24 at 23:47

If you are referring to the situation from back-in-the-day, with less ambiguous devices, and no auto-mdi(x) as a matter of academic inquiry, as it rarely matters today:

In summary: Routers (which are hosts) and workstations(etc) require straight-thru cables to connect to switches. Host-to-host connections require cross-over cables, as do switch-to-switch connections. Cross-over cables are not required to interconnect switches if one switch has a cross-over port. If both switches connect via two cross-over ports, a cross-over cable is then required.

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Most if not all devices now comes with auto sense network ports in which the logic of the signal get negotiated between the devices, probably in any popular piece of equipment shipped in last decade you can ignore if a cross patch is needed. As wrong cable was the most common source of issues for soho users, and as now most hw is powerful enough, you can assume autosensing is now a pretty much standard feature.

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