6 ms·

Interconnections: Bridges, Routers, Switches, and Internetworking Protocols 2nd Edition - Radia Perlman Every 2-3 years, particularly in the periods when I'm n

Interconnections: Bridges, Routers, Switches, and Internetworking Protocols 2nd Edition - Radia Perlman Every 2-3 years, particularly in the periods when I'm not actively in network engineering, I re-read this book from start-finish - and it just completely centers my mindset with regards to pretty much every fundamental topic in Network Engineering. There almost didn't need to be a 2nd Edition - most of the major topics were covered in 1st edition - the only major difference is the use of lots of protocol examples. The core material itself is timeless. Here is just one gem from Chapter 5 - "Hubs, Switches, Virtual Lans and Fast Ethernet" "I originally resisted adopting the term switch. Unlike thing, switch sounds like a word you'd apply to a well-defined concept, so it makes people assume that there is a crisp definition that everyone else knows. I thought the world was already confusing enough with the terms bridge and router. Unfortunately, people coined the word switch assuming they were inventing a new concept, somehow different from a bridge or a router. And there were various independent product concepts named switch. As "switch" vendors expanded the capabilities of their products, the products wound up being functionally the same as bridges and routers, usually a hybrid or superset. One cynical (and ungrammatical) definition I use for switch is "a marketing term that means fast." Almost all products these days are some hybrid or superset of bridges and routers. So maybe it's right for the industry to settle on a new word, switch, as a more generic term for a box that moves data."

deleted 2y ago
[deleted]
codazoda 2y ago
I don’t know if my understanding is correct but I always thought of a switch in contrast to a network hub. A hub broadcasts incoming packets to all its ports while a switch keeps a table and broadcasts only to the port that MAC is plugged into. That table is likely called a “routing table”, which probably drives some confusion. I always thought of a router as an internet connected switch. In addition, I always thought of a modem as something that can speak the language of the line (phone lines originally) instead of just the network protocol. I’m not a network pro and these concepts could be totally wrong in my mind. Not sure why I’m spewing them out, other than to give myself something to solidify in the future.
- dfex 2y ago
  You're mostly there - your hub definition is spot on - it's basically an electrical repeater and doesn't inspect the packet in any way* and operates at half-duplex. Switches (specifically Layer 2 switches) will send broadcast frames to all ports*, but traffic that is unicast to a specific MAC address will only be sent to the port where that MAC address was learnt. To keep track of the MAC address to port mappings, a switch will have one or more "forwarding" or "MAC-address" tables. Routers (and Layer 3 switches) are not necessarily Internet connected, but will mostly be seen in larger networks. Being mostly Ethernet-based these days, they maintain two tables - an ARP table (mapping IP Addresses to MAC Addresses) and a routing table (mapping IP prefixes/routes to destination IP addresses). When an IP packet comes into a port, the router will consult it's routing table and find the most specific route that matches the destination of the packet. From the destination IP of the route, it will then determine the egress interface that it should send the packet towards, then use the ARP table to work out the destination Ethernet MAC address for the Ethernet frame it will construct to transport the IP packet in on it's way to the next-hop router. * During the early 00s there were "Dual-Speed Hubs", which were basically two hubs (one 10Mbps, one 100Mbps) joined together internally via a two-port Ethernet switch. Fortunately the price of 100Mbps Ethernet switches kept falling and they weren't around too long. * Provided those ports are all members of the same broadcast domain/VLAN
dang 2y ago
My copy had a blurb from tptacek on the cover. I don't know which edition that was. After reading your comment I'm sorry I didn't keep the book!
- tptacek 2y ago
  It's the 2nd edition. I can't tell you how weird it was to be asked for that blurb. I was 22! It is a great book, though.
red-iron-pine 2y ago
i always thought switch came from the old telephone "switchboards", which were usually handled inside of large buildings. you'd call the operator to route (e.g. a router) your call to the right location, and then the switchboard operator inside said location. routing itself came from postal routing, IIRC

deleted 2y ago

[deleted]

codazoda 2y ago

I don’t know if my understanding is correct but I always thought of a switch in contrast to a network hub. A hub broadcasts incoming packets to all its ports while a switch keeps a table and broadcasts only to the port that MAC is plugged into. That table is likely called a “routing table”, which probably drives some confusion. I always thought of a router as an internet connected switch. In addition, I always thought of a modem as something that can speak the language of the line (phone lines originally) instead of just the network protocol. I’m not a network pro and these concepts could be totally wrong in my mind. Not sure why I’m spewing them out, other than to give myself something to solidify in the future.

dfex 2y ago
You're mostly there - your hub definition is spot on - it's basically an electrical repeater and doesn't inspect the packet in any way* and operates at half-duplex. Switches (specifically Layer 2 switches) will send broadcast frames to all ports*, but traffic that is unicast to a specific MAC address will only be sent to the port where that MAC address was learnt. To keep track of the MAC address to port mappings, a switch will have one or more "forwarding" or "MAC-address" tables. Routers (and Layer 3 switches) are not necessarily Internet connected, but will mostly be seen in larger networks. Being mostly Ethernet-based these days, they maintain two tables - an ARP table (mapping IP Addresses to MAC Addresses) and a routing table (mapping IP prefixes/routes to destination IP addresses). When an IP packet comes into a port, the router will consult it's routing table and find the most specific route that matches the destination of the packet. From the destination IP of the route, it will then determine the egress interface that it should send the packet towards, then use the ARP table to work out the destination Ethernet MAC address for the Ethernet frame it will construct to transport the IP packet in on it's way to the next-hop router. * During the early 00s there were "Dual-Speed Hubs", which were basically two hubs (one 10Mbps, one 100Mbps) joined together internally via a two-port Ethernet switch. Fortunately the price of 100Mbps Ethernet switches kept falling and they weren't around too long. * Provided those ports are all members of the same broadcast domain/VLAN

dang 2y ago

My copy had a blurb from tptacek on the cover. I don't know which edition that was. After reading your comment I'm sorry I didn't keep the book!

tptacek 2y ago
It's the 2nd edition. I can't tell you how weird it was to be asked for that blurb. I was 22! It is a great book, though.

red-iron-pine 2y ago

i always thought switch came from the old telephone "switchboards", which were usually handled inside of large buildings. you'd call the operator to route (e.g. a router) your call to the right location, and then the switchboard operator inside said location. routing itself came from postal routing, IIRC