In my previous post Encapsulation of PDUs On Trunk Ports, I showed what happens to PDUs when you change the configuration of a trunk. You may have noticed that there are typically three different types of Ethernet encapsulations that we
Some History on VLAN 1 in Cisco Switches
Over the years, there has been a lot of discussion on if VLAN 1 in Cisco switches is special or not. Does it have any characteristics that other VLANs don’t? I covered some of this in the Is VLAN 1
802.1Q-Tagged Frames Through Unmanaged Switch – Forwarded or Dropped?
As a follow-up to the post yesterday on native VLANs, there was a question on what would happen to 802.1Q-tagged frames traversing an unmanaged switch. Unmanaged in this case being a switch that does not support VLANs. While this might
1000BASE-T Part 4 – Link Down Detection
In the previous three parts, we learned about all the interesting things that go on in the PHY with scrambling, descrambling, synchronization, auto negotiation, FEC encoding, and so on. This is all essential knowledge that we need to have to
1000BASE-T Part 2 – Deepdive
In 1000BASE-T Part 1, we reviewed the layers and what their purpose is. Now we’re going to go much deeper into the layers that relate to the PHY, which is PCS, PMA, and Autonegotiation. First though, let’s review the objectives
1000BASE-T Part 1 – Introduction
How does Ethernet detect that a link goes down? This, what I thought was a simple question, I asked myself a couple of weeks ago. I realized I didn’t have a very good answer. I realized I had more to
Ethernet, STP, Topology change and the behaviour of Ethernet
Introduction This post is inspired by a post at IEOC about Uplinkfast and TCN which can be found here. Before we get to those parts, let’s recap how Ethernet and STP work together. Spanning Tree The Spanning Tree Algorithm builds
Detecting Network Failure
Introduction In todays networks, reliability is critical. Reliability needs to be high and convergence needs to be fast. There are several ways of detecting network failure but not all of them scale. This post takes a look at different methods
The history of Ethernet – DIX vs 802.3
I’m planning to do a post on BPDUs sent by Cisco switches and analyze why they are sent. To fully understand the coming post first we need to understand the different versions of Ethernet. There is more than one version?
Ethernet – notes
RJ 45 pinouts 10-BASE-T and 100BASE-TX uses pairs two and three, gigabit Ethernet uses all four pairs. Pinout for straight cable: 1-1;2-2;3-3;6-6 Pinout for crossover cable: 1-3;2-6;3-1;6-2 A standard PC transmits on pair one and two and receives on three