Cisco Ethernet Interfaces are set to auto negotiation for their speed and duplex settings by default, which means that both devices on a link will automatically negotiate the best settings for their connection. They will first share their speed and duplex capabilities and then decide on which ones to take.
If auto negotiation is not active on both sides, the interfaces will find their speed settings based on the incoming electrical signal, as long as the fixed sides uses a speed which is supported by the other side.
So basically we could set the speed on one side to fix and on the other side to auto, even though its not a good practice, it is still possible.
This article is a good match of what I have/should/want to read and what I had to change on my home network to get the functions I want it to have. I will have to write a follow up to the last IPv6 at Home article, since the layout including the configuration got some flaws. But that will be covered in another article. For now I gonna write something about configuring PPPoE to get a working Internet Access over a Digital Subscriber Line (DSL). Please note that I use a 12.4 IOS version, as far as I know, the PPPoE configuration is a bit different (keyword vpdn) on older versions (it sure it is on 12.2, but not sure on 12.3).
Point-to-Point Protocol over Ethernet (PPPoE, defined in RFC2516) is widely used in DSL environments since the public telephone networks usually use ATM as transport protocol. So to get Ethernet over the telephone network, a protocol must be used which both transport protocols support which in that case is PPPoE.
Ok, this is going to be the first article in a series of articles about the CCIE recertification topics (some, not all..) I’m currently going through to get myself recertified 🙂 And to have some of the base topics handy for the future. As long as Cisco doesn’t change all of them 😉
**Update 8th of October 2010**
As it looks like the information below only works for “older” switches like 3550 and 2950. Newer Switches like 3560, 3750 or 2960 do behave different!
As every Ethernet device, switches do use MAC addresses to address their own interfaces, including the Switch Virtual Interfaces (SVIs). They do use a “base” MAC address for the SVI(s) and increase it by one for every interface, starting with the very first.