Q & A on Detecting and fixing routing problems
Q: Is there a way that you can mend a broken route? If a gateway along the route has gone down, is there a way to specify that the packets should search for an alternate gateway, so as to be able to reach their destination?
A: I'll assume you are asking about an IP gateway (aka IP router), and also that you are asking from a user's perspective rather than the perspective of someone who manages the gateway.
- A user cannot send a message to an IP gateway that causes the IP gateway
to change it's routes.
- If it is working correctly, protocol software running on an IP gateway
will find alternative paths automatically, and will change the routing
table to use an alternative (assuming, of course, an alternative path
to the destination exists).
- A sender can specify a "source route" when transmitting an IP datagram.
The source route lists a set of IP gateways along a path to the
destination (each IP gateway that handles the datagram uses the
source route information rather than the local routing table).
- Few applications or operating systems actually have a simple way for an average user to specify the source route option described in #3.