How to troubleshoot a router contract with router settings

During the router setup process, the network communication is not abnormal, the router can successfully route packets to the target network, but the packets sent from the router fail, the fault shows that the router ping the target network failed, this fault is more common. Let's take a look at a typical case.

Failure phenomenon

When the network configuration is complete, the administrator discovers that when a ping is sent from a PC (218.59.245.195) to the target network (218.59.245.65/26), the router R1 can successfully forward the packet, but from R1 to the target network ( 218.59.245.65/26 a ping failure occurred while sending a ping.

Fault split panel

Track the path that the ping passes through. Check the R1 routing table, and the destination address 218.59.245.65 can match 0.0.0.0/0 in the routing table. Check the routing tables for R2, R3, and R4 to find the routing table entries that match the destination address.

Tracks the path that the ICMP response response packet passes through. To complete this step, to explicitly respond to the source address of the packet, when the PC sends a ping, the response Reply packet's destination address is 218.59.245.195. When a router R1 a ping, the target address of the response reply packet is 218.59.0.146. The routing table entries that match 218.59.245.195 are found against the R4 routing table, and no routing table entries that match the destination address 218.59.0.146 are found. It appears that the ICMP response reply packet was discarded at R4 processing, so a PMG failure occurred when the ping was sent from R1 to the target network R4 (218.59.245.65/26).

Fault resolution

With router setup, add a static route to the 218.59.0.144/30 on the router R4, and the next hop is 218.59.0.214. When you are done, when R1 sends a ping to R4, you find that the router's contract failed to resolve.

Ping failed network failure does not affect the normal communication of the network, the process of elimination is very simple, generally through simple router settings can be resolved. But in the analysis and elimination of network fault, we should consider the complete communication process.

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