7 ms·

Which proves my point. Real world stuff rarely fits neatly into theoretical models/categories. Real world Layer 3 Switches are a hybrid between a router and a

Which proves my point. Real world stuff rarely fits neatly into theoretical models/categories. Real world Layer 3 Switches are a hybrid between a router and a pure layer 3 switch. In fact they're just a really fast router. A normal edge router switches based on IP and a bunch of extra rules. These extra rules range from firewall stuff to QoS. These extra rules need software to process. A core router is what is now called a Layer 3 Switch. It just cares about the IP address and because of that can be done in hardware making it really fast. It's still a router because as you said it still has routing tables based on networks and subnets. I don't think anyone makes a true (non-router) layer 3 switch. The only use case I can think of would be a campus wide WiFi network.

jlgaddis 9y ago
"switching" is a layer 2 term. At layer 2, frames are switched. At layer 3, packets are routed. An edge router routes, based upon the destination IP adress (unless you have policies that cause a packet to be sent elsewhere). Layer 3 implies routing, by the way. A "pure layer 3 switch" is called a router.
- Avernar 9y ago
  Again, theory and reality rarely line up neatly. A switch moves packets between devices inside a network and a router moves packets between networks. Calling one a frame and one a packet is splitting hairs and irrelevant to whether something is a router or a switch. Using a *BSD/Linux box I can make a L2 router. I can also make an real (non routing) L3 switch. And since "pure layer 3 switch" is my made up term I think I get to define what it means, thank you very much. It's something that doesn't route, or in other words, you can have the same network (i.e. subnet) on multiple ports. Then we get into the definition of a network. Is it a building, a department, or how about multiple buildings all over the world? Or how about the network of a backbone provider? Their core "routers" are really switches as they pass packets to other devices inside their network. And the network gear manufacturers are muddying things even more. Their definition of routing or switching is whether it's done in software or hardware. That's why they're calling some of their equipment a Layer 3 Switch. As I said, that really is just a fast router based on the above definition. The easiest way to distinguish switching vs routing is whether the packets move to the same or different subnet. It's a good rule of thumb but there are always exceptions. You can take an L2 switch and replace it with an L3 switch on your network and everything IP based will work as if nothing had happened. You'd just get less broadcast traffic.
  - jlgaddis 9y ago
    > The data link layer is concerned with local delivery of frames ... [0] > The network layer is responsible for packet forwarding including routing ... [1] IP operates at layer 3. Layer 3, by definition, implies routing. > Their definition of routing or switching is whether it's done in software or hardware. No. No, it's not. I think that, in general, you kinda sorta know what you're talking about (although you've got a few things incorrect) but the way you keep screwing up basic terminology really makes me wonder. In networking, router, switch, frame, and packet are all clearly defined -- as are the various layers and the PDUs involved at each of them -- and mean specific things but you can call 'em whatever you want to, I suppose. [0]: https://en.wikipedia.org/wiki/Data_link_layer https://en.wikipedia.org/wiki/Data_link_layer [1]: https://en.wikipedia.org/wiki/Network_layer https://en.wikipedia.org/wiki/Network_layer
    - Avernar 9y ago
      You've completely missed my points and at the same time gave a perfect example of someone who's rigedly trying to follow the OSI model. > IP operates at layer 3. Layer 3, by definition, implies routing. Layer 3 does not imply routing! I can shut down my internet link and still use a layer 3 protocol to talk to my file server from my workstation. No routing is happening because the packets are not leaving my network. > > Their definition of routing or switching is whether it's done in software or hardware. > No. No, it's not. I know it's not. That's what the hardware manufactures are saying on their websites. It's stupid but it shows how blurry the line is between switching and routing. > I think that, in general, you kinda sorta know what you're talking about (although you've got a few things incorrect) but the way you keep screwing up basic terminology really makes me wonder. I know exactly what I'm talking about and know my terminology. The problem is you're trapped in the OSI model and can't see where things overlap. > In networking, router, switch, frame, and packet are all clearly defined -- as are the various layers and the PDUs involved at each of them -- and mean specific things but you can call 'em whatever you want to, I suppose. Routing and switching are not as clearly defined as you think. Just google routing vs switching and you get many variations. Some talk about frames and packets, others about MACs and IPs, but the core principle common to them all is that switching is in network and routing is out of network. A few also mention that routing is a more specific form of switching. Your issue is you mistakenly belive that routing and switching are each tied to a specific layer in the OSI model. With that belief, yeah, frames are switched and packets are routed. But as I and others here have stated, things in the real world don't always follow the theoretical model. Take for example the idea seen frequently online of doing away with the ethernet layer and having IP as the frame format. So now in the OSI model what was in layer 3 and 4 now become 2 and 3. Or does some of it drop and some stay in the same spot? It quickly turns into a mess. Mainly because what was supposed to happen in layer 2 (flow control and acknowlegements) is happening in layer 4 (TCP). Mainly because the designers of TCP did not follow the OSI model. My point is that you can't use what was defined in the OSI model to rigedly define what's happening in real world protocols. As I said, you can create a switch that operates at layer 3. It would learn what nodes are on each port by watching ARP requests. It would send out ARP replies for nodes on other ports with its own MAC and would also have to forward DHCP requests. This device would function exactly as a switch. You could have the same subnet on many ports and it would work. You can move a node from one port to another and it would work. A router can't do those things. A router forwards packets based on their destination network. But if you can't understand that and are stuck in the OSI model, we've esentially taken what was at layer 3 and put it in layer 2. The old layer 2 is just there for comatibility. You could even rip out one of the ethernet links between two of these layer 3 switches and replace it with a serial link that just transmits IP packets and everything would work as normal.

jlgaddis 9y ago

"switching" is a layer 2 term. At layer 2, frames are switched. At layer 3, packets are routed. An edge router routes, based upon the destination IP adress (unless you have policies that cause a packet to be sent elsewhere). Layer 3 implies routing, by the way. A "pure layer 3 switch" is called a router.

Avernar 9y ago
Again, theory and reality rarely line up neatly. A switch moves packets between devices inside a network and a router moves packets between networks. Calling one a frame and one a packet is splitting hairs and irrelevant to whether something is a router or a switch. Using a *BSD/Linux box I can make a L2 router. I can also make an real (non routing) L3 switch. And since "pure layer 3 switch" is my made up term I think I get to define what it means, thank you very much. It's something that doesn't route, or in other words, you can have the same network (i.e. subnet) on multiple ports. Then we get into the definition of a network. Is it a building, a department, or how about multiple buildings all over the world? Or how about the network of a backbone provider? Their core "routers" are really switches as they pass packets to other devices inside their network. And the network gear manufacturers are muddying things even more. Their definition of routing or switching is whether it's done in software or hardware. That's why they're calling some of their equipment a Layer 3 Switch. As I said, that really is just a fast router based on the above definition. The easiest way to distinguish switching vs routing is whether the packets move to the same or different subnet. It's a good rule of thumb but there are always exceptions. You can take an L2 switch and replace it with an L3 switch on your network and everything IP based will work as if nothing had happened. You'd just get less broadcast traffic.
- jlgaddis 9y ago
  > The data link layer is concerned with local delivery of frames ... [0] > The network layer is responsible for packet forwarding including routing ... [1] IP operates at layer 3. Layer 3, by definition, implies routing. > Their definition of routing or switching is whether it's done in software or hardware. No. No, it's not. I think that, in general, you kinda sorta know what you're talking about (although you've got a few things incorrect) but the way you keep screwing up basic terminology really makes me wonder. In networking, router, switch, frame, and packet are all clearly defined -- as are the various layers and the PDUs involved at each of them -- and mean specific things but you can call 'em whatever you want to, I suppose. [0]: https://en.wikipedia.org/wiki/Data_link_layer https://en.wikipedia.org/wiki/Data_link_layer [1]: https://en.wikipedia.org/wiki/Network_layer https://en.wikipedia.org/wiki/Network_layer
  - Avernar 9y ago
    You've completely missed my points and at the same time gave a perfect example of someone who's rigedly trying to follow the OSI model. > IP operates at layer 3. Layer 3, by definition, implies routing. Layer 3 does not imply routing! I can shut down my internet link and still use a layer 3 protocol to talk to my file server from my workstation. No routing is happening because the packets are not leaving my network. > > Their definition of routing or switching is whether it's done in software or hardware. > No. No, it's not. I know it's not. That's what the hardware manufactures are saying on their websites. It's stupid but it shows how blurry the line is between switching and routing. > I think that, in general, you kinda sorta know what you're talking about (although you've got a few things incorrect) but the way you keep screwing up basic terminology really makes me wonder. I know exactly what I'm talking about and know my terminology. The problem is you're trapped in the OSI model and can't see where things overlap. > In networking, router, switch, frame, and packet are all clearly defined -- as are the various layers and the PDUs involved at each of them -- and mean specific things but you can call 'em whatever you want to, I suppose. Routing and switching are not as clearly defined as you think. Just google routing vs switching and you get many variations. Some talk about frames and packets, others about MACs and IPs, but the core principle common to them all is that switching is in network and routing is out of network. A few also mention that routing is a more specific form of switching. Your issue is you mistakenly belive that routing and switching are each tied to a specific layer in the OSI model. With that belief, yeah, frames are switched and packets are routed. But as I and others here have stated, things in the real world don't always follow the theoretical model. Take for example the idea seen frequently online of doing away with the ethernet layer and having IP as the frame format. So now in the OSI model what was in layer 3 and 4 now become 2 and 3. Or does some of it drop and some stay in the same spot? It quickly turns into a mess. Mainly because what was supposed to happen in layer 2 (flow control and acknowlegements) is happening in layer 4 (TCP). Mainly because the designers of TCP did not follow the OSI model. My point is that you can't use what was defined in the OSI model to rigedly define what's happening in real world protocols. As I said, you can create a switch that operates at layer 3. It would learn what nodes are on each port by watching ARP requests. It would send out ARP replies for nodes on other ports with its own MAC and would also have to forward DHCP requests. This device would function exactly as a switch. You could have the same subnet on many ports and it would work. You can move a node from one port to another and it would work. A router can't do those things. A router forwards packets based on their destination network. But if you can't understand that and are stuck in the OSI model, we've esentially taken what was at layer 3 and put it in layer 2. The old layer 2 is just there for comatibility. You could even rip out one of the ethernet links between two of these layer 3 switches and replace it with a serial link that just transmits IP packets and everything would work as normal.