GNS3 Analog ICMP redirection

A gateway is essentially an IP address of a network to another network. For example, network A and network B, network A's IP address range is "192.168.1.1~192." 168.1.254 ", the subnet mask is 255.255.255.0; The IP address range for Network B is" 192.168.2.1~192.168.2.254 "and the subnet mask is 255.255.255.0. In the absence of a router, TCP/IP communication between the two networks is not possible, even if the two network connections on the same switch (or hub), the TCP/IP protocol will determine the subnet mask (255.255.255.0) on the two network hosts in a different network. To achieve communication between the two networks, you must pass through the gateway. If the host in Network a discovers that the destination host for the packet is not on the local network, forwards the packet to its own gateway, which is then forwarded by the gateway to Network B's gateway, and the gateway of Network B is forwarded to a host on network B.

ICMP redirect packets are one of the ICMP control messages. In a particular case, when the router detects that a machine is using a non-optimized route, it sends an ICMP redirect message to the host requesting the host to change the route. The router also forwards the initial packet to its destination. There are two common scenarios in which ICMP redirection occurs: 1) When the router receives data from an interface and needs to forward that data from the same interface, 2) when the router discovers that the source IP address and the next hop belong to the same network segment from an interface to the data from the remote network. r1:conf tint f0/0no shutdownip add 192.168.1.1 255.255.255.0no IP routingend r2:conf tint f0/0no shutdownip add 192.168.1. 254 255.255.255.0int lo1ip Add 2.2.2.2 255.255.255.255end r3:conf tint f0/0no shutdownip add 192.168.1.2 255.255.255.0ip R  Oute 2.2.2.2 255.255.255.255 192.168.1.254end then R3 ping R2. Ping 2.2.2.2 is guaranteed to be able to connect. R1:ip Default-gateway 192.168.1.2ping 2.2.2.2 three-line grab package is as follows:

GNS3 Analog ICMP redirection