Ask HN: What nonfiction books do you keep rereading?

Systemantics by John Gall: https://en.wikipedia.org/wiki/Systemantics

The Reign of Quantity and the Signs of the Times - Rene Guenon (1945).

An esoteric book that summarises everything as a direction which moves away from quality and towards quantity. Here is an excerpt that uses this system to analyse modern workplace anonymity:

"[...] tendency to uniformity demands that individuals shall be treated as mere numerical 'units', thus realizing equality by a leveling down, for that is the only direction in which equality can be reached 'in the limit' [...] Anyone who wonders what happens to the individual in such conditions will find that [...] he is so to speak reduced to his substantial aspect, and this amounts to saying that he becomes scarcely more than [...] 'a body without a soul'. From such an individual the qualitative or essential aspect has indeed almost disappeared ('almost', because the limit can never actually be reached); and [...] the individual really no longer has any 'name' that belongs to him, because he is emptied of the qualities which that name should express; he is thus really 'anonymous', but in the inferior sense of the word. This is the anonymity of the 'masses' of which the individual is part and in which he loses himself, those 'masses' that are no more than a collection of similar individuals, regarded purely and simply as so many arithmetical 'units'. 'Units' of that sort can be counted, and the collectivity they make up can thus be numerically evaluated, the result being by definition only a quantity; but in no way can each one of them be given a denomination indicating that he is distinguished from the others by some qualitative difference."

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

Happy by Derren Brown - not a self help book, more an introduction to classical Greek and Roman philosophy framed around stoicism and a dash of Epicureanism. While it does include mental exercises you can do to aid in a stoic sense of self, I've never found the need to do them, but have definitely become more stoic, and by extension happier, as a result of reading it.

PeopleWare. I read it and then re-read it every year.