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QuinStreet does not include all companies or all types of products available in the marketplace. It's like i'm missing how it logically fits in the OSI model?
Obviously at layer 2 to 3 but Does it change according to the application which sends the data, which determines if UC or MC is needed? There are use cases and I think that is what you are asking. One use case would be MS Loadbalancing. Microsoft has unicast and multicast mode that use locally administered unicast source mac addresses that are used differently depending on the mode. For example, in unicast mode, both hosts share the same unicast source mac address. However, traffic is never sourced from this locally administered address.
The result is that it is never learned by the switches and therefore always flooded to both hosts as well as the rest of them on the vlan. Then, based on an algorithm, the hosts filter the traffic based on their loadbalancing criteria.
Multicast is a destination thing. Since frames are sourced from a host, the source is that hosts mac address. Multicast destinations should have the multicast bit set when the destination is on the same vlan. When it is routed multicast, the last hop of the packet's journey would have this bit set to one. It's not an optional header, the field always exists. I'm not a developer so I cannot say how applications signal this to the IP or ethernet process how that is handled.
Organizationally unique identifier
The standards would mostly include how it looks on the wire. How these protocol data units are produced is most likely left up to the software developers, the operating systems and the APIs that are used. I feel like you're not completely satisfied with the answer. I certainly encourage asking why. However, in some cases, there is no clear cut answer withouth talking to some of those responsible for the standardization.
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In this case, it was foreseen by the IEEE that there might be a need to have configurable mac address and multicast destinations, and that was how they chose to implement it. They could have just as easily added some overhead to the header and created a field.
They chose to implement it the way they did and the rest of the industry pretty much adapted over time to the more widely used standard. When a vendor or developer chooses to use Ethernet, they just have to follow the predetermined standard.
MAC address - Wikipedia
At the end of the day, the IEEE probably developed this over a long period of time with a lot of input. There was probably a lot of discussion around little endian versus big endian and the relevant hardware platforms of the day. There probably are a lot of really interesting answers to your question.
Today, the answer is because it is the standard. It is also worth noting that these techniques were used in Token Ring as well. I must say, although it wasn't very easy to understand, this chatting with you has been very helpful and most of all eductional.
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So, thank you for that. Although I first try to find different resources like books or whatever, because the provided documents whithin these organizations tend to be too technical sometimes.
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Anyways, just trying to pass my exam in a decent way On the question of why use local MAC address assignment, there are some cases where a hardware burn't in address BIA is not available all be it not on Cisco switches. A common example of this is virtual machines e. VMWare where there is no physical network interface card so the virtualisation software must make up a MAC address everytime a logical network interface card is created.
I would expect that the only thing that would be examined for the CCNA exam would be the existance of these two special bits in the MAC address and then to be able to identify whether a given MAC address is unicast or multicast, local or global from the hexadecimal representation of the address.
If you have access to a Cisco switch, have a look at the MAC address table and see if you can work out why the entries are there:. Note that the second command allows you to cheat and see which of the addresses were multicast without you having to work it out yourself! Thank you for your contribution.
I also think this won't be questionned in depth about on a CCNA exam at least they didn't on my first exam , but I'm mostly concerned with getting to understand the fundamental networking mechanisms. I ran over those too fast on my first trial and so I'm not about to make the same mistake again. Anyways, also a very useful answer, tomorrow at work, I'm certainly going to enter one of those on one of our switches.