What Are the Best Network Diagnostics Tools?

PING (Packet Internet Groper), an Internet packet explorer, a program for testing network connections ^[1] . Ping is a service command that works in the application layer of the TCP / IP network architecture. It mainly sends ICMP (Iternet Control Message Protocol) Echo request messages to specific destination hosts to test whether the destination station is reachable Learn about its status ^[2] .

Ping is used to determine whether the local host can successfully exchange (send and receive) data packets with another host. Based on the returned information, it can be inferred

Under normal circumstances, when you use the Ping command to find the problem or check the network operation, you need to use many Ping commands. If all are running correctly, you can believe that there is no problem with basic connectivity and configuration parameters; if some The Ping command is malfunctioning. It can also indicate where to look for problems. ^[3]

When the physical link connectivity and routing settings are correct, the Ping command still does not work. The following problems may occur:

(1) Ping the gateway as soon as the network cable is plugged into the switch, ignoring the convergence time of the spanning tree. Of course, newer switches support rapid spanning tree, or some administrators simply turn off the spanning tree protocol of the user port (accessport), the problem is solved ^[5] .

(2) No matter how many nodes pass in the middle, as long as there are nodes (including end nodes) that filter the ICMP information packet, it is normal for the Ping to fail. The most common is the behavior of firewalls ^[5] .

(3) Some router ports do not allow users to ping ^[5] .

(4) ICMP messages cannot be received within the default time (2 seconds) due to timeout between devices on the network. Reasons for the timeout are: the host does not have enough time and resources to respond; the path is too long and the TTL value is 0 when the destination is not reached; the last router will send back ICMP timeout information; extended pings are used to increase the response wait time interval, etc ^[5] .

(5) The introduction of NAT will cause a one-way ping. NAT can play a role of concealing the internal address. When pinging from the inside to the outside, it can ping through because the mapping relationship of the NAT table exists. When pinging the internal host from the outside, it is impossible to find the NAT access list of the border router. ^5] .