Answer to Question #89459 in Computer Networks for Mokete

Question

Explain in detail the ping process between pc1 and router

Answer 1

The PING team is, perhaps, the most used network utility of a command line. PING is present at all versions of all operating systems with support of network and is simple and convenient means of poll of knot on a name or its IP address.

For exchange of office and diagnostic information in network the special protocol of the operating messages of ICMP(Internet Control Message Protocol) is used. The ping team allows to execute sending the operating message like Echo Request (the type is equal 8 and it is specified in ICMP message heading) to the addressed knot and to interpret the answer received from it in a look, convenient for the analysis. The data field of the sent icmp-package usually contain symbols of the English alphabet. In response to such inquiry, the interviewed knot is burned up to send an icmp-package of the same data which were accepted, and type of the message Echo Reply (the type code is equal in ICMP heading to 0). If at exchange of icmp-messages there is any problem, then the utility of ping will output information for its diagnostics.

Application of PING for step-by-step diagnostics of problems of Internet access:

The generalized scheme of connection of the computer (the tablet, the laptop of a home network) with remote final knot it is possible to present as follows:

As a home network the most widespread network with IP addresses 192.168.1.0/255.255.255.0 is used. It is about IPv4 – the IP protocol of version 4 where for addressing 4 bytes are used. IP-of the address can be presented in the form of decimal values of the bytes divided by points. Each device in network has to have the unique address. Except the address, in network settings the mask of network (a subnet mask) is used. The mask has the same format of representation, as well as the address. The combination of the address and a mask determines the range of addresses which belong to local network - 192.168.1.0-192.168.1.255. The first and last addresses of range are not appointed to separate network devices as are used as the address of network and the broadcasting address. Usually the address of a router is done equal 192.168.1.1 or 192.168.1.254. It is not the obligatory standard, but in practice is used quite often. Single bits of a mask define a constant component of the IP address of network, and zero — allocated to separate knots. Value 255 is a byte with the bits established in unit. The mask of network serves as means of determination of range of the IP addresses belonging to local network. Devices with such addresses are achievable locally, without routing use. Routing is a way of data exchange with the network devices which are not belonging to this local network via the special device - router. Routers represent specialized computers with several network interfaces and the specialized software providing transfer of IP packages between the sender and the recipient who are in different networks. Several routers, depending on complexity of a route can participate in such transfer. A house router — the simplest kind of the router which provides transfer of the packages addressed in external networks to the router following along a route in network of provider. The following router checks approachibility of the address of final knot locally, and or sends it data, or transfers them to the following router according to the table of routes. So occurs until data do not reach the recipient or package life time will end.

The PING team can be used for diagnostics of separate knots:

ping 127.0.0.1 is a ping of the loopback interface. It has to be carried out without mistakes if are established and there are in operating state network program components.

ping the IP or a name - a ping to own address or a name. Has to come to the end without mistakes if all software of the IP protocol are established and the network adapter is serviceable.

router ping IP address - router ping IP address - has to be carried out if the network interface card of the computer is serviceable, the cable or wireless connection used for connection to a router is serviceable and the router is serviceable. Besides, the IP settings have to be such that the address of the computer and a router belonged to one subnet. Usually it so when network tunings are performed automatically by means of the DHCP server of the router.

ping google.com - to execute knot poll with the name google.com. If poll comes to the end with a mistake, then not only lack of contact with the router of provider, but also impossibility of definition of the address of the google.com hub because of problems with software of permission of names can be the cause.

ping - n 1000 - l 500 192.168.1.1 - to execute ping of 1000 times with use of messages, 500 bytes long. Ping can be carried out by packages of standard length 32 bytes without mistakes, and on long — with mistakes that is characteristic for wireless connections at the low level of a signal in the conditions of intensive hindrances.

ping - n 1 - r 9 - w 1000 google.com - to execute ping of 1 times (a key - n 1), to give a route for the first 9 transitions (-r 9), to expect the answer 1 second (1000 ms).

As a result of implementation of this command also trace of a route is displayed:

Exchange of packages of google.com [87.250.251.11] with 32 bytes of data: The answer from 87.250.251.11: number of bytes =32 time =36 мs TTL=54 route: 81.56.118.62 ->  81.56.112.1 ->  10.109.11.9 ->  10.109.11.10 ->  195.34.59.105 ->  195.34.52.213 ->  195.34.49.121 -> 195.34.52.213 ->  87.250.239.23  Ping statistics for 87.250.251.11: Pa: send = 1, recived = 1, lost = 0 (0% loss) Approximate time of reception-transmission in ms: Minimum = 36 мs, Maximum = 36 мs, Average = 36 мs

In this example, between the sender and the recipient of packages the chain of 9 routers is built. It is necessary to consider the fact that in the version of the utility ping.exe for Windows, the number of transitions can accept value from 1 to 9. In cases when this value is not enough, the tracert team is used.

Absence an echo answer not always is a malfunction sign as sometimes for safety reasons, some knots are adjusted on ignoring of the echo requests sent to PING. The microsoft.com hub and some routers in networks of small providers can be an example.