Ethernet Switches

Errata for Ethernet Switches

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The errata list is a list of errors and their corrections that were found after the product was released.

The following errata were submitted by our customers and have not yet been approved or disproved by the author or editor. They solely represent the opinion of the customer.

Color Key: Serious technical mistake Minor technical mistake Language or formatting error Typo Question Note Update

Version Location Description Submitted by Date Submitted
PDF Page 4
5th paragraph

From the text: 'The way the switch “learns” is fairly simple. Like all Ethernet interfaces, every port on a switch has a unique factory-assigned MAC address. However, unlike a normal Ethernet device that accepts only frames addressed directed to it, the Ethernet interface located in each port of a switch runs in promiscuous mode.' Each port having a unique MAC address didn't sound right to me. To verify, I used Wireshark on three computers connected to a Cisco SD216 unmanaged 16 port 100 Mb switch. Each computer was connected to a different switch port. I then captured spanning tree frames from the switch. On each of the three computers, the frames contained the same source MAC address. This would indicate that only one MAC is used for the entire switch and not a unique MAC address for each port. Also, a different MAC address on each port would break STP, as it normally depends on the MAC address when determining the root switch. With different MACs on each port, the root could change, depending on which port is used. The same error appears in the ePub version of the book.

James Knott  Dec 22, 2013