5 ms·

AFAIK, the general perception is that http is a transport & upper protocol. Not an application layer protocol. Anyway, OSI model is mostly a mental picture tha

AFAIK, the general perception is that http is a transport & upper protocol. Not an application layer protocol. Anyway, OSI model is mostly a mental picture that bear little practical relevance. If someone want to follow OSI model and devise a new model, then itself is a wrong approach. TCP/IP was invented out of solving real internetworking problems, without regarding much to the OSI model or any pre-defined model per-se. As always, David Clark's "e2e principle" (https://en.wikipedia.org/wiki/End-to-end_principle https://en.wikipedia.org/wiki/End-to-end_principle) probably is the only guiding principle (or a after-fact summary) that is worth following.

MrTonyD 9y ago
I think it was back in the 80's when I was in a networking standards group (was it ANSI?? It's been a long time) and we were trying to define programming layers on top of sockets for UNIX. The effort completely failed - but the write-up about what we were trying to accomplish seemed to live on - getting revised and revised until it became the OSI model - with all its layers that we sort-of tried to implement. Of course, the new drivers and software layers didn't actually work, and the performance was abysmal, so the effort was abandoned. But the press and everyone else really liked the understandable text write-up about networking, which almost nobody understood at the time, so the write-up seemed to get a life of its own. Since then I've been scorned at job interviews and among peers for not having the model memorized, or not being able to explain the meaning of various layers. Just another example of our crazy methods of screening job candidates. Answering stupid questions from stupid people means more than actual experience.
- Avernar 9y ago
  When I used to deal with people straight out of school they would always talk about the OSI model and it would drive me crazy. Everything we did would have to be categorized. What layer is this in, what layer is that in. I just want you to plug that Ethernet cable into that switch port and configure the static IP address in the software so we can get the hell out of here and have a beer. No amount of explaining that stuff in the real world doesn't neatly fit into those categories would get them to shut up about it. One guy nearly had a mental breakdown when he first came across a tunnel. "How can you have two network layers?!?" One day I was installing something in a computer lab at a college and on the wall was a giant poster of the OSI model with all the protocols imaginable listed on it. I had to fight the urge to set it on fire... Yes, models are great for teaching and for certain types of discussions (L2 vs L3 switches) but the real world is always more complicated and the lines in the model tend to blur. Take the basic computer model taught to new students with the CPU, memory, input, output, storage, networking all neatly connected in that familiar diagram. A real computer is never connected that way. Memory is all over the place, storage can be directly on the CPU or hundreds of feet away in another box, etc. Students quickly figure out that the computer model is just a teaching tool. Just holding a motherboard quickly makes them see that. But for networking they seem to hang on to the OSI model like if it were a piece of flotsam after a shipwreck.
  - gerdesj 9y ago
    "Two network layers?!?" Hah, yes and in the real world we do far weirder things than that. VXLANs running over [whatever], OpenVPN inside IPSEC and then ssh or RDP inside that. Obviously you don't do all of that routinely but I've seen some crazy shit to work around something or link up odd setups. I have seen a triple nested VPN: IPSEC within IPSEC and OpenVPN inside. I'm sure many here will have seen similar or worse.
  - deleted 9y ago
    [deleted]
  - dkffkld 9y ago
    > L2 vs L3 switches The fuck are those? Some Cisco bullshit as usual? I swear to God they must've already come up with every possible combination of switch and router by now.
    - Avernar 9y ago
      A Layer 2 switch is something that works on the data link layer. A normal Ethernet switch falls into this category and the switching is done by MAC address. A layer 3 switch is something that works on the network layer. It switches using the IP address. A layer 3 switch is not a router. It does not switch based on the subnet/network mask. It just remembers which IP is on which port just like an Ethernet switch remembers which MAC address is on which port.
      - icedchai 9y ago
        Layer 3 switches have routing / forwarding tables... They qualify as routers.
        Avernar 9y ago
        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.
- jacquesm 9y ago
  Sure... https://news.ycombinator.com/item?id=14053716 https://news.ycombinator.com/item?id=14053716 Stop making stuff up.
justonepost 9y ago
Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
justonepost 9y ago
Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.
Avernar 9y ago
The end to end principle pretty much made the flow control and re-transmission functions of the LLC sublayer of the data link layer obsolete. So now we pay a 6 to 8 byte penalty (8 bytes if the MAC can tell us the packet length) on every frame transmitted. Wired/optical Ethernet does not normally use LPD (LLC Protocol Discrimination, i.e. 802.2 LLC/SNAP) but unfortunately WiFi does. So in 2014 while the author is advocating for the data link layer to ensure packets are received by other devices on the channel like the current OSI model does, the IEEE is encouraging new standards to use EPD (Ethernet Protocol Discrimination) instead of LPD. The IEEE just wants the LLC sublayer to only do multiplexing of protocols now. The author completely missed how the upper layer protocols, i.e. TCP/IP, has made some parts of the lower layer protocols unnecessary. Having a basic model is good thing for classifying different parts of the network and makes discussions clearer. But in the real world things rarely fall into categories that neatly.

MrTonyD 9y ago

I think it was back in the 80's when I was in a networking standards group (was it ANSI?? It's been a long time) and we were trying to define programming layers on top of sockets for UNIX. The effort completely failed - but the write-up about what we were trying to accomplish seemed to live on - getting revised and revised until it became the OSI model - with all its layers that we sort-of tried to implement. Of course, the new drivers and software layers didn't actually work, and the performance was abysmal, so the effort was abandoned. But the press and everyone else really liked the understandable text write-up about networking, which almost nobody understood at the time, so the write-up seemed to get a life of its own. Since then I've been scorned at job interviews and among peers for not having the model memorized, or not being able to explain the meaning of various layers. Just another example of our crazy methods of screening job candidates. Answering stupid questions from stupid people means more than actual experience.

Avernar 9y ago
When I used to deal with people straight out of school they would always talk about the OSI model and it would drive me crazy. Everything we did would have to be categorized. What layer is this in, what layer is that in. I just want you to plug that Ethernet cable into that switch port and configure the static IP address in the software so we can get the hell out of here and have a beer. No amount of explaining that stuff in the real world doesn't neatly fit into those categories would get them to shut up about it. One guy nearly had a mental breakdown when he first came across a tunnel. "How can you have two network layers?!?" One day I was installing something in a computer lab at a college and on the wall was a giant poster of the OSI model with all the protocols imaginable listed on it. I had to fight the urge to set it on fire... Yes, models are great for teaching and for certain types of discussions (L2 vs L3 switches) but the real world is always more complicated and the lines in the model tend to blur. Take the basic computer model taught to new students with the CPU, memory, input, output, storage, networking all neatly connected in that familiar diagram. A real computer is never connected that way. Memory is all over the place, storage can be directly on the CPU or hundreds of feet away in another box, etc. Students quickly figure out that the computer model is just a teaching tool. Just holding a motherboard quickly makes them see that. But for networking they seem to hang on to the OSI model like if it were a piece of flotsam after a shipwreck.
- gerdesj 9y ago
  "Two network layers?!?" Hah, yes and in the real world we do far weirder things than that. VXLANs running over [whatever], OpenVPN inside IPSEC and then ssh or RDP inside that. Obviously you don't do all of that routinely but I've seen some crazy shit to work around something or link up odd setups. I have seen a triple nested VPN: IPSEC within IPSEC and OpenVPN inside. I'm sure many here will have seen similar or worse.
- deleted 9y ago
  [deleted]
- dkffkld 9y ago
  > L2 vs L3 switches The fuck are those? Some Cisco bullshit as usual? I swear to God they must've already come up with every possible combination of switch and router by now.
  - Avernar 9y ago
    A Layer 2 switch is something that works on the data link layer. A normal Ethernet switch falls into this category and the switching is done by MAC address. A layer 3 switch is something that works on the network layer. It switches using the IP address. A layer 3 switch is not a router. It does not switch based on the subnet/network mask. It just remembers which IP is on which port just like an Ethernet switch remembers which MAC address is on which port.
    - icedchai 9y ago
      Layer 3 switches have routing / forwarding tables... They qualify as routers.
      - Avernar 9y ago
        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.
jacquesm 9y ago
Sure... https://news.ycombinator.com/item?id=14053716 https://news.ycombinator.com/item?id=14053716 Stop making stuff up.

justonepost 9y ago

Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.

justonepost 9y ago

Well, there are themes that are evolving that are worth cataloging in a new logical model that can help guide further innovation. I agree though, the model itself isn't the root.

Avernar 9y ago

The end to end principle pretty much made the flow control and re-transmission functions of the LLC sublayer of the data link layer obsolete. So now we pay a 6 to 8 byte penalty (8 bytes if the MAC can tell us the packet length) on every frame transmitted. Wired/optical Ethernet does not normally use LPD (LLC Protocol Discrimination, i.e. 802.2 LLC/SNAP) but unfortunately WiFi does. So in 2014 while the author is advocating for the data link layer to ensure packets are received by other devices on the channel like the current OSI model does, the IEEE is encouraging new standards to use EPD (Ethernet Protocol Discrimination) instead of LPD. The IEEE just wants the LLC sublayer to only do multiplexing of protocols now. The author completely missed how the upper layer protocols, i.e. TCP/IP, has made some parts of the lower layer protocols unnecessary. Having a basic model is good thing for classifying different parts of the network and makes discussions clearer. But in the real world things rarely fall into categories that neatly.