Re: Routing table question
> "David H. Silber" <dhs@orbits.com> writes:
>
>
> I still don't understand something. Doesn't the line:
>
> 192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0
>
> mean "send everything addressed to IP's 192.168.1.* through default
> gateway"? But this way the kernel will be sending communications for
> 192.168.1.1 through 209.226.71.1. So I must be wrong in translating
> the line above...
It more means "send everything addressed to a host on the
192.168.1.0/24 network to -no- gateway."
The gateway column specifies which machine to gateway through, so
should be host addresses, not network addresses. "0.0.0.0" does not
mean "default", but rather "none".
Perhaps a bigger example will make it clearer...
(Abbreviated) routing table:
Destination Gateway Iface
192.168.1.0/24 0.0.0.0 eth0
192.168.2.0/24 192.168.1.254 (eth0)
192.168.3.0/24 192.168.1.253 (eth0)
209.226.71.0/24 0.0.0.0 eth1
0.0.0.0/0 209.226.71.1 (eth1)
This is your setup, but I've added two more local nets that have
gateways on the 192.168.1.0 network.
The interfaces in parenthesis are computed by the routing algorithm,
not set by route or ifconfig.
If you send a packet to 192.168.1.34, the routing algorithm would see
that you have a direct connection (no gateway) to 192.168.1.0/24, which
is the network for your destination, so it would know to send through
the eth0 interface directly to 192.168.1.34.
If you send a packet to 192.168.2.34, the routing algorithm would see
that 192.168.1.254 is the gateway, and it's precomputed that the
gateway is on eth0, so it would send your packet for ...2.34 to
...1.254 on eth0. Similarly, a packet to ...3.34 would be sent to
...1.2553 on eth0. Presumably, the two gateways would forward it along.
If you sent a packet to 208.4.23.5, the routing algorithm would see
that there is no defined route to that machine, so it uses the default
route, and sends it to 209.226.71.1 for forwarding.
Clearer?
>
> --
> Arcady Genkin
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> of eternal blessedness in the other world..." (S. Kierkegaard)
>
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