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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

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
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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.
      - 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.
        9y ago
jlgaddis 9y ago
Then you end up with people like I clean up after, who don't know the difference between layers 2 and 3 and can't understand out why putting 1200 clients (spread across a few dozen sites, linked by microwave connections) on the same layer 2 segment causes problems.

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.
    - 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.
      - 9y ago

jlgaddis 9y ago

Then you end up with people like I clean up after, who don't know the difference between layers 2 and 3 and can't understand out why putting 1200 clients (spread across a few dozen sites, linked by microwave connections) on the same layer 2 segment causes problems.