Routing on network prefix only
IP address assignment
Here is the routing table for my previous laptop, when at home and connected to both Ethernet and Wi-Fi. It's from the route command (very similar to netstat -r).
Genmask Flags Metric
Ref Use Iface
default asgard61 0.0.0.0 UG 100 0 0 enp0s25
default asgard 0.0.0.0 UG 600 0 0 wlp3s0
10.0.0.0 0.0.0.0 255.255.255.0 U 600 0 0 wlp3s0
10.0.6.0 0.0.0.0 255.255.255.0 U 100 0 0 enp0s25
10.2.5.0 0.0.0.0 255.255.255.0 U 0 0 0 tap0
link-local 0.0.0.0 255.255.0.0 U 1000 0 0 enp0s25
The destinations are at left. Only the first two have the G flag, and thus have a gateway; the last four are link-level routes. The Gateway column lists the next_hop, where applicable; for non-G route entries, there is no next_hop and everything must be delivered directly. The prefix length for each Destination address is specified by Genmask, where you count the number of 1-bits. Note that the two valid next_hop entries are listed by hostname.
From the newer ip route list command:
via 10.0.6.1 dev enp0s25 proto
default via 10.0.0.1 dev wlp3s0 proto dhcp metric 600
10.0.0.0/24 dev wlp3s0 proto kernel scope link src 10.0.0.7 metric 600
10.0.6.0/24 dev enp0s25 proto kernel scope link src 10.0.6.5 metric 100
10.2.5.0/24 dev tap0 proto kernel scope link src 10.2.5.1 linkdown
169.254.0.0/16 dev enp0s25 scope link metric 1000
Here, destinations are
listed as destaddr/mask. The link-level routes are listed as "scope link".
The metric values are arbitrary; smaller is better. The src values
represent the IP address of this machine on the given subnet. Some spaces
have been added in an attempt to get similar values to line up.
Ethernet: start Chapter 2
Ethernet diagram with NIs
Ethernet collision timeline
scaling Ethernet to 100 Mbps, etc
switched full duplex => collision-free!
basic Ethernet-switch learning algorithm