![]() ![]() There are three methods by which a Switch can forward frames. When this happens, the Switch happily forwards the frame out the appropriate switchport. Ideally, of course, the Switch will have an entry in its MAC Address Table for every Destination MAC it comes across. Moreover, when the intended device receives the frame, a response will be generated, which when sent to the Switch will allow the switch to learn and create a MAC Address Table mapping that unknown device to its switchport. If they are the intended device, however, then the Switch can rest satisfied knowing it was able to deliver the frame successfully. If they are not the intended recipient, they will simply silently drop the frame. And though not ideal, this is perfectly normal. The NIC of each connected device will receive the frame and take a look at the Destination MAC address field. Of course, so will every other device connected to that particular Switch. ![]() This action is known as Flooding.įlooding assures that if the intended device exists and if it is connected to the switch, it will definitely receive the frame. In such cases, the Switch’s only option is to simply duplicate the frame and send it out all ports. However, despite the learning process above, it is unavoidable that a Switch will at some point receive a frame destined to a MAC address of which the Switch does not know the location. This table can then be used to smartly forward frames to their intended destination. Sooner or later, as each connected device inevitably sends something, the Switch will have a fully populated MAC Address Table. The MAC address table starts out empty, and every time a Switch receives anything, it takes a look at the Source MAC address field of the incoming frame. It uses the Source MAC and the switchport the frame was received on to build an entry in the MAC Address Table. One of the goals of the Switch is to create a MAC Address Table, mapping each of its switchports to the MAC address of the connected devices. Specifically, a Switch will use the Source MAC address and Destination MAC address to make its forwarding decisions. Switch FunctionsĪ Switch primarily has four functions: Learning, Flooding, Forwarding, and Filtering: Learningīeing a Layer 2 device, a Switch will make all its decisions based upon information found in the L2 Header. We will start by looking at the individual switch functions, and then take a look at an animation which shows their collaborative operation. It might be worth reviewing that section before proceeding. This article will be the practical application of everything that was discussed when we looked at a Switch as a key player in packet traveling. We will take a look at what happens for communication from Host to Host through a Switch. In this article, we will add a common network device: a switch. ![]() In the last article, we looked at everything that happens for two hosts to communicate directly with one another. Use the navigation boxes to view the rest of the articles. This article is a part of a series on Packet Traveling - everything that happens in order to get a packet from here to there. ![]()
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