3 ms·

I believe the parent isn’t complaining that routers do things at layers 1-3, but that they also do things at layer 4 (namely, block anything that isn’t TCP or U

by comex 6y ago

I believe the parent isn’t complaining that routers do things at layers 1-3, but that they also do things at layer 4 (namely, block anything that isn’t TCP or UDP).

TeMPOraL 6y ago
Isn't this just a naming issue, though? I remember initially being confused by "switches" doing layer 3 stuff and "routers" doing layer 4 stuff, but over the years I've just learned to revise the definitions in my head; now I consider "router" to be a box that works on most layers (up to all of them with a sufficiently smart router), and "switch" to be just a cheaper router with more Ethernet ports. Layers seem OK for dividing protocols, but networks tend to be managed across all layers, so it's understandable all that functionality gets put in a single device - possibly internally structured one. I'm not a network engineer, but what I understand from the admin panel of my Mikrotik router is that the mental model here is a bunch of virtual devices, each working on one of the layers, packaged into one physical box.
- walrus01 6y ago
  In terms of equipment capabilities we most certainly have switches that have sets of layer 3 capabilities, even a ten year old cisco 3750x can do basic OSPF, BGP, EIGRP etc. Often referred to as an enhanced or layer 3 switch. https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3560-x-series-switches/data_sheet_c78-584733.html https://www.cisco.com/c/en/us/products/collateral/switches/c... But you for sure wouldn't call it a router because it has nowhere near the routing table RAM, routing ability, or full set of routing configuration parameters as you would want to use on a dedicated purpose router. For your mikrotik, if you open it up or if you look at someone's teardown of one, what you'll see is a set of gigabit ethernet switch chips (perhaps 1 ASIC per every 4 ports) under heatsinks, that have purely layer 2 feature sets only. And then one CPU that runs the mikrotik routerOS which does layer 3 things. The mikrotik will have different levels of performance in packets per second capability for traffic flows that stay at purely layer 2, and another level of capability in Mbps and pps at layer 3. The OS on the mikrotik knows how to tell the switch chips how to do things at layer 2 (define this vlan, define this trunk, group certain ports into the same fabric, do 802.1x stuff, etc). for instance here's a block diagram of a mikrotik rb4011: https://i.mt.lv/cdn/product_files/RB4011iGSplusRM_180903.png https://i.mt.lv/cdn/product_files/RB4011iGSplusRM_180903.png
- junon 6y ago
  Aside from extra hardware, routers generally have a firewall built-in and can perform NAT translations and otherwise act as a gateway. They do DHCP in most cases, too. Of course when you start to look at enterprise setups things get a little more complicated. Since routers act as gateways, they have their own IP address too. Switches are not gateways. They join two physical segments and mask them as a single logical segment. They do routing only in the most basic of senses - moving packets between the physical lines.

by comex 6y ago

I believe the parent isn’t complaining that routers do things at layers 1-3, but that they also do things at layer 4 (namely, block anything that isn’t TCP or UDP).

TeMPOraL 6y ago

Isn't this just a naming issue, though? I remember initially being confused by "switches" doing layer 3 stuff and "routers" doing layer 4 stuff, but over the years I've just learned to revise the definitions in my head; now I consider "router" to be a box that works on most layers (up to all of them with a sufficiently smart router), and "switch" to be just a cheaper router with more Ethernet ports. Layers seem OK for dividing protocols, but networks tend to be managed across all layers, so it's understandable all that functionality gets put in a single device - possibly internally structured one. I'm not a network engineer, but what I understand from the admin panel of my Mikrotik router is that the mental model here is a bunch of virtual devices, each working on one of the layers, packaged into one physical box.

walrus01 6y ago
In terms of equipment capabilities we most certainly have switches that have sets of layer 3 capabilities, even a ten year old cisco 3750x can do basic OSPF, BGP, EIGRP etc. Often referred to as an enhanced or layer 3 switch. https://www.cisco.com/c/en/us/products/collateral/switches/catalyst-3560-x-series-switches/data_sheet_c78-584733.html https://www.cisco.com/c/en/us/products/collateral/switches/c... But you for sure wouldn't call it a router because it has nowhere near the routing table RAM, routing ability, or full set of routing configuration parameters as you would want to use on a dedicated purpose router. For your mikrotik, if you open it up or if you look at someone's teardown of one, what you'll see is a set of gigabit ethernet switch chips (perhaps 1 ASIC per every 4 ports) under heatsinks, that have purely layer 2 feature sets only. And then one CPU that runs the mikrotik routerOS which does layer 3 things. The mikrotik will have different levels of performance in packets per second capability for traffic flows that stay at purely layer 2, and another level of capability in Mbps and pps at layer 3. The OS on the mikrotik knows how to tell the switch chips how to do things at layer 2 (define this vlan, define this trunk, group certain ports into the same fabric, do 802.1x stuff, etc). for instance here's a block diagram of a mikrotik rb4011: https://i.mt.lv/cdn/product_files/RB4011iGSplusRM_180903.png https://i.mt.lv/cdn/product_files/RB4011iGSplusRM_180903.png
junon 6y ago
Aside from extra hardware, routers generally have a firewall built-in and can perform NAT translations and otherwise act as a gateway. They do DHCP in most cases, too. Of course when you start to look at enterprise setups things get a little more complicated. Since routers act as gateways, they have their own IP address too. Switches are not gateways. They join two physical segments and mask them as a single logical segment. They do routing only in the most basic of senses - moving packets between the physical lines.