This sets all of the class D (multicast) IP routes to go via "eth0".
Without these options, route displays the current contents of the routing tables. NOTE: The specified gateway must be reachable first.
If a packet comes into the system and has a destination in the range 192.168.1.0 through 192.168.1.255, then it is forwarded to the gateway *, which is 0.0.0.0 — a special address which represents an invalid or non-existant destination.
So, in this case, our system will not route these packets.
This usually means that you have to set up a static route to the gateway beforehand. force the route to be associated with the specified device, as the kernel will otherwise try to determine the device on its own (by checking already existing routes and device specifications, and where the route is added to). If dev If is the last option on the command line, the word dev may be omitted, as it's the default.
If you specify the address of one of your local interfaces, it will be used to decide about the interface to which the packets should be routed to. set the initial round trip time (irtt) for TCP connections over this route to I milliseconds (1-12000). Otherwise the order of the route modifiers (metric - netmask - gw - dev) doesn't the normal loopback entry, using netmask 255.0.0.0 (class A net, determined from the destination address) and associated with the "lo" device (assuming this device was prviously set up correctly with ifconfig(8)).