TCP/IP replicated strated I Reading Notes 3-Routing Mechanism, routing rules and routing protocols

1. traceroute first sends an IP packet whose TTL is 1 to the target address. The first router drops the TTL by 1, discards the packet, and sends an ICMP time exceeded message to the source address, in this way, the first route in the path is retrieved. traceroute then sends an IP packet whose TTL is 2 to the target address, so that each route in the path is retrieved in sequence. finally, the path of the Unreachable message from the destination address has been retrieved.

2. traceroute can also specify a strict path and a loose path in the IP Option of the IP header. A strict path specifies the exact path through which the IP package passes. A loose path specifies the router that the IP package must pass. the specified number is also limited by the IP Option size. You can only specify nine.

3. if the host or router does not know how to send an IP packet (no default route entry), an ICMP error is generated. If the IP packet is generated by itself, a "Network unreachable" ICMP message is sent; if not, send the "Host Unreachable" ICMP message.

4. the route command, route daemon (usually a user process, used to exchange route information with other routers through the routing protocol), and ICMP redirect messages change the route table. there is also an ICMP route discovery message, which can be used to update the default route entry through the solicited message of the machine that is started with advertisement and the new boot. this route discovery function is usually implemented by a user daemon.

5. the widely used IGP includes rip (using UDP port 520) and osfp; the widely used EGP includes EGP and BGP.

When the network interface is initialized, the rip request. Route daemon periodically sends messages to metrics of different networks to update the routes of other routers in the network.