IP and MAC address’

Orangeb said:
Does that make sense? The layer 3 info it needs and receives is slightly different to the layer 2 info it receives.
Click to expand...

This is always the case when routing between subnets.

If routing locally inside the same broadcast domain (bunch of hosts connected to a switch) everything is known locally by the switch (in it's cam table <database of known mac addresses learnt from the network>) and all of the hosts use ARP to learn about each other's MAC addresses, so all the information required to communicate is present.

However, if routing to a different network we need to route at layer-3 (via a router) the host can't send traffic directly to the host because it's remote - it needs to do it via a gateway (router) therefore, instead of the final destination host MAC address in the layer-2 header, the layer-2 destination address of the router's gateway interface is used - so the packet flows directly to the router.

The MAC address of the router would be learnt by the host via ARP.
 
`carping on?! - did I miss something?
Yes, those explanations were helpful. I don’t know if I’m making progress or not. I now understand the ARP stuff, and MAC address’ etc. Sometimes Chuck goes pretty quick - maybe I’m not the only person who has noticed that - however I think the guy is great, and his way of explaining is good. I think I’m going to do a mix of his CCNA course and professor messer’s one too. That way, hopefully when i take it, I’ll pass!
 
I think you are missing the whole point of the OSI layer model. It is meant to encapsulate complexity to each layer. You are going into a particular rabbit hole on layer 2 and layer 3 which is a useful one admittedly, but you need to get to grips with why the OSI model exists. You could find yourself in much crazier rabbit holes if you aren't careful :D
 
Hi People,
I am learning things for the CCNA exam - primarily using Network chuck. He is talking about the top layers of the OSI model, mainly the Application layer. BUT, if you have never played around wirth this stuff, the term http doesn’t mean much. I know it means hyper text transfer protocol, but when I start to look into what it actually does, it says its a protocol - BUT isn’t the whole OSI model and the TCP/IP just a protocol? Do they mean the http is not a seperate protocol, but just part of the larger model - layer 7? From what I can tell its liike its name “application” - web browsers, and the type of things they move - images, videos etc.

That might seem a very basic, stupid question, but referring to it as a seperate protocol just seems confusing to me, when the whole OSI is a protocol. Why would they have a whole protocol system and then make layer 7 a protocol of its own - can’t see how that would work!
 
Orangeb said:
Hi People,
I am learning things for the CCNA exam - primarily using Network chuck. He is talking about the top layers of the OSI model, mainly the Application layer. BUT, if you have never played around wirth this stuff, the term http doesn’t mean much. I know it means hyper text transfer protocol, but when I start to look into what it actually does, it says its a protocol - BUT isn’t the whole OSI model and the TCP/IP just a protocol? Do they mean the http is not a seperate protocol, but just part of the larger model - layer 7? From what I can tell its liike its name “application” - web browsers, and the type of things they move - images, videos etc.

That might seem a very basic, stupid question, but referring to it as a seperate protocol just seems confusing to me, when the whole OSI is a protocol. Why would they have a whole protocol system and then make layer 7 a protocol of its own - can’t see how that would work!
Click to expand...
OSI is not a protocol. OSI is a layer model to aid understanding of network stacks.
 
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