On 5/17/21 1:35 PM, Hendrik Boom wrote:
I have found several authoritative-looking web pages on instructions to
display and edit the routing tables.

But none of them explains what the routing tabe entries *mean*.

The routing table entries show the way your host can find other networks, local or remote.  Each entry describes how to reach every connected network, and what it considers to be local to your connection.  A special route, the default route, shows how to reach networks outside of your local scope.

Other routing table entries may show how to reach other networks.

When you configure your interface ethv0, a route to its local network will be shown, for example:

with "ip route":

192.168.1.0/24 dev ethv0 proto kernel scope link src 192.168.1.10

with "netstat -rn" :

Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface 192.168.1.0     0.0.0.0         255.255.255.0   U         0 0          0 ethv0

They both describe the same route, to network 192.168.1.0, with a 24 bit netmask (meaning you have 8 bits left for hosts in your network, from 192.168.1.1 to 192.168.1.254, with 192.168.1.0 being used to reference the network itself, and 192.168.1.255 as the broadcast address, where you would send data meant for every host in your network).

If you want to reach say network 192.168.90.0/24 which is reacheable via host 192.168.1.2, you could add a route like this:

ip route add 192.168.90.0/24 via 192.168.1.2

A special route to network 0.0.0.0/0 is the default route, which is used to reach any network of which your host has no knowledge. With ip show it looks like this:

default via 192.168.1.1 dev ethv0 onlink

with netstat -rn it looks like this:

Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
0.0.0.0         192.168.1.1   0.0.0.0         UG        0 0          0 ethv0

With route it can be added as:

route add -net default gw 192.168.1.1

once you have your interface configured.

--
Hector Gonzalez
ca...@genac.org

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