Why Use Crossover or Straight-Through Copper to Connect PC to Switch?

ciscopacket-tracerswitch

How come a PC can connect to a Switch using Crossover copper, and sometimes a Straight-Through Copper?

The below topology is in my Cisco Network in Packet Tracer.

Best Answer

Newer switches can automatically detect if a cable is crossover or straight through and negotiate the correct mode in order for the host to connect correctly, also called MDIX auto.

Auto-MDIX on an Interface

When automatic medium-dependent interface crossover (auto-MDIX) is enabled on an interface, the interface automatically detects the required cable connection type (straight through or crossover) and configures the connection appropriately. When connecting switches without the auto-MDIX feature, you must use straight-through cables to connect to devices such as servers, workstations, or routers and crossover cables to connect to other switches or repeaters. With auto-MDIX enabled, you can use either type of cable to connect to other devices, and the interface automatically corrects for any incorrect cabling.

Auto MDI-X is enabled by default on Cisco switches.

The Cisco 2950 does not support this feature.

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Cisco MAC Address – How Can There Be More Than One MAC Address on a Single Switch Port?

You can have more than one MAC address on a switch port if:

You have a switch connected to it. Could be another managed switch (like a Cisco) or an unmanaged switch (like a consumer Netgear or Linksys switch).
You have a virtual server host attached to it with multiple virtual machines sharing the NIC.
You're using a VoIP phone to carry data for a computer. In this case, you'll have a trunk running to the phone from the switch and a second ethernet cable running from the phone to a computer.

Switch – VLans Cisco Packet tracer

You need an access list to block inter-VLAN traffic. There will be one for each subinterface. For example

access-list 10 deny 172.1.0.0 0.0.0.127
access-list 10 deny <vlan 30>
access-list 10 deny <etc>
access-list 10 permit any

interface fa 0/0.10
access-group 10 out

If you've never configured access list before, note the following:

The subnet masks in the statement are "wildcard masks." They are the one's complement of a normal mask.
You need to add a line in your access list for every VLAN you want to block.

Best Answer

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