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Ports VS Interfaces What Are The Differences

Posted by: admin  :  Category: Exam Preps, Routing, Switching, Troubleshooting




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Over the long course of my career I have heard many of my colleagues refer to these two terms interchangeably, although this is actually not true and may cost you a wrong answer on an exam such as Cisco’s CCNA or CCNP which could make the difference between you passing the exam or not. Let us take a look at the differences in these two terms.

Ports:

The Port resides at layer 1 of the OSI model, the Physical layer. This layer defines the electrical and physical specifications for a device, such as copper or fiber media as well as the voltages, line impedance, signal timing, and the physical layout of pins for the connecting device such as twisted pairs, coaxial or in the case of fiber cable single mode or multi-mode.

Interfaces:

The Interface resides at layer 2 of the OSI model, the Data Link layer. This layer defines the functional and procedural method of transferring data between network devices, such as Serial, Ethernet, FDDI, and Token-Ring. Additionally this layer may provide the ability to detect and maybe correct errors that might occur at the physical layer.

Virtual Interfaces:

There are a number of interfaces that have no physical connection to any device such as Loopbacks, Lines, and VLANs. These interfaces are referred to as virtual interfaces, and although these interfaces have no physical connection they can still be addressed and accessed by other devices in a network. Interfaces such as Loopback interfaces are very useful in insuring devices are reachable with many routing protocols.

Sub interfaces are another form of virtual interface and are used in WAN connections like Frame-Relay, and VLAN Trunks between routers and switches when creating a router on a stick to route between VLANs or deploying DHCP addressing for multiple VLANs.

In conclusion the line between Ports and Interfaces may be blurry, and in the real world the two terms may be used interchangeably but there is a difference and you need to understand the difference not only to pass an exam, but to help you properly configure network interfaces on Cisco routing and switch equipment and help you troubleshoot some complex networking issues. A good way to remember this is you use some form of media to physically connect a network port to another network device port and you configure a network interface with some form of protocol to allow communication between network devices on a LAN or WAN.

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4 Responses to “Ports VS Interfaces What Are The Differences”

  1. Anonymous Says:

    very informative! thanks

  2. David Christie Says:

    Barry, Although I sort of agree with you, when it comes to Cisco Networking and particularly Cisco exams there are a lot of blurry areas. I have been teaching data networking for quite a number of years and have taught Cisco courses.

    If you look at almost any Cisco official training material and support documentation regarding the configuration of Cisco devices the terms port and interface are interchangeable. Whether you are looking at VLAN configuration, MAC Address Tables or Routing and Switching, the term port is probably used more than interface. Cisco themselves often refer to layer 2 ports or layer 3 ports, so it really isnt clear cut.

    When it comes to passing Cisco exams then it is all about making note of how the training material refers to ports and interfaces.

    I wont ramble on because it is a subject that could be discussed over and over, but if this could mean the difference between passing or failing a cisco exam then I have to say that it really is nitpicking.

    Anyway, it is a very good discussion point.

    David

  3. admin Says:

    Thank you David, I agree that the terms are use interchangeable in the real world and I myself have used them in the same manner, but I was asked the question on an interview and was commended on the correctness of my answer. I do not believe that it was the reason I got the job, but it did show I had a fair understanding of the 7 layer ISO model, or at least the first 2 layers.

  4. kphul Says:

    This is really great.

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