General Information about Router Technology.

Not only in the business field, but also in the private home are computer networks used with various devices. A central role is played by the router as a connection node between the Internet and the local home network. The meaning is usually underestimated, the tasks are varied as the adjoining graphic shows. The router is used to exchange data between the Internet and the PC, the laptop, the printer, the network hard disk drive, the network camera, the smart phone, etc.

An IP address (Internet Protocol) is an address on the computer network that is used to address network-enabled devices. The conversion of a computer or device name into a computer-readable byte pattern is done with the Domain Name System (DNS). Each device (host), which provides services in a network, has additionally a defined (globally unique) hardware address, the MAC address (Media Access Control), which is used to identify the device in the network. The MAC address is located in the router at the second data level and is always mentioned together with the local IP address which is located at the third data level. The different data levels are explained in the OSI model, more details can be found in the appendix. According to the Open Systems Interconnection (OSI) model, the data exchange between systems is subdivided into functional levels or layers, and the same structures ensure the compatibility of the systems with each other.

The direct access to the PC or laptop from the Internet should be avoided for security reasons. Exceptions exist in remote maintenance work by means of a virtual network connection (VNC) to the computer. A data exchange between an external laptop and the hard disk drive in the local home network should be possible by means of a FTP program (File Transfer Protocol). The network-capable hard disk drive, the network camera and the printer should be directly accessible from the Internet. For example, the netcam is used for home surveillance in case you are absent, incidents can be recorded on a hard disk drive while the netcam sends you a message to your Smart Phone, i.e. your home can be controlled remotely. Apart from any other remote controls, the Smart Phone can remotely print a message on the printer at home via VPN (Virtual Private Network).

Requirements for the Router.

1. Normally, after checking the access data the network provider assigns the user (client) for the data communication out of its IP range an available IP address. The client goes into the Internet and addresses via a browser a domain name like ‘ARTandENGINEERING.net’. In the case of the response of a network camera, the IP address to the router respectively the netcam must be known and always be the same, otherwise the router with its netcam cannot be found from the Internet. All devices in the local network are stored with their local IP address in the router. The router serves as a central exchange. Only when a port address (e.g. 8876) for the network device is specified, the router can forward the request to the device.

2. However, the local network behind the router has to be heavily protected against foreign intruders from outside. The router has to act as a physical barrier between the Internet and the individual devices in the local network. In order not to influence the performance of the individual devices within the local network, no unauthorized requests may be forwarded. Otherwise under a possible flood of data, the local network could collapse.

3. The globally scarce IP address space does not allow providing each device (host) in the local network with an individual globally valid IP address. The router therefore has the task the data transfer of the individual hosts batchwise to manage, i.e. the multiple batch data exchange of the individual hosts via the Internet is only performed with one and the same external IP address. A response to a request must then return to the same sender in the local network.

Settings and Operation of the Router.

The router will either automatically assign each host a local IP address via the Domain Host Configuration Protocol (DHCP), e.g. 192.168.2.101, or the local address is entered manually through the Control Panel. In order to reach always the same host in the local network, the local IP address must not change here either. Under Windows 7 you will find the Internet Protocol Version 4 (TCPv4) in the Network and Sharing Centre. The Transmission Control Protocol (TCP / IP) defines the transition between the external IP and the local IP address and includes a DNS server address. In addition to the local IP, however, additional addresses must be entered here that define closer the position of the host to the router. Here are to mention: the subnet mask, the default gateway and the DNS server address.

IP addresses are divided into workspaces and classes A, B and C. Most workspaces has the class A with 256³ = 16,777,216, then class B with 256² = 65,536 and finally class C with only 256. In the latter case, those would be those between 192.168.2.0 and 192.168.2.255. The workspaces contain the addresses, such as IP addresses, DNS addresses, and subnet masks of the various services.

Symbolically, the subnet mask can be explained as follows: In the case of a nationwide valid telephone number, all digits are written consecutively, the information about where the prefix number ends and the connection number begins is missing. Therefore, the two parts are e.g. separated by a slash or a bracket comment. This type of information is included in the subnet mask or in the prefix number, e.g. 255.255.255.0. In the representation of an IP network, the subnet mask in this symbol corresponds to the specification of the area code. The local network behind the router must always have the same "area code", otherwise the hosts cannot communicate with each other.

The default gateway is the default node between 2 networks. The IP address is as an e.g. 192.168.100.1 and is at the same time the access address to the router via an Internet browser.

Domains are usually specified by names, e.g. ‘Willi-Mauser.net’. Computers can only handle addresses with numbers. The conversion takes place with the "Domain Name System (DNS)". For the conversion of the domain name ‘Willi-Mauser.net’ an appropriate DNS server must be available.

Data packets between the hosts on the local network and the Internet must not be swapped. This is regulated in the router by means of the NAT protocol (Network Address Translation). Without being directly visible, the data packets are assigned a port address that is associated with the local IP of the host, e.g. 192.168.2.101:2133. The local IP (192.168.2.101) together with the port address (2133) is called socket address. The same data packet has a different socket address on the router's website. Both socket addresses must communicate with each other in response to a request, the data packets are handed over by handshake. Port addresses are divided into areas that have different tasks. The port addresses between 8000 and 8888 are e.g. to find a program or a host on the local network from the Internet via the external IP and the local IP. As an example, the Smart Phone searches a file located on the desktop by means of a special program and saves it on the SD card of the Smart Phone. Data will be collected. In the other direction, a document can be printed directly from the smart phone via the printer connected to the PC. Data is being sent. In the special program-parts on the Smart Phone and on the PC, this service requires the external and local IP address as well as port addresses. Access to the program parts is encrypted. For security reasons, you only place the accessible folder on the desktop surface. The processes are carried out without an i-Cloud, the service of a third party is not required and the privacy remains secure.

The backup of the data should be done on a separate hard disk drive that is decoupled from the internet (not shown). Also advantageous is regular cloning of the computer hard disk including the operating system on a physically identical external hard disk drive. In the eventual case of a total crash just the plates are exchanged.

Appendix

Structure of the 7-layer OIS model (Open Systems Interconnection).

The OIS model explains the framework under which data is exchanged between different systems (networks, devices):

1.  Layer: physical layer, wire, fiber optic, radio relay.
2.  Layer: Hardware addresses of the PCs and network devices (MAC addresses).
3.  Layer: routing protocols, IP addresses, port addresses.
4.  Layer: Services like TCP protocol and
     UDP-protocol (User Datagram Protocol).
5.  Layer: Special communications using the SMB protocol
     to print and connect to Windows shares.
6.  Layer: Presentation layer e.g. for MPEG, TIFF, GIF and ASCII formats.
7.  Layer: applications, execution layer of programs.

The path of the data from one system to another begins e.g. in the network A at the layer 7 and then goes down to layer 1 of the network A, over the "wire", the data are passed in the network B. In network B, the data then pass through layers 1 to 7. In the case of a so-called virtual (apparent) connection, the data information is passed in the same layer from one device to the other.

Testing procedures under DOS on a PC.

The command line is accessed via Start (Execute) or by pressing the [Win] + [R] key simultaneously. With the entry of 'CMD' and pressing the 'Enter' key, a black DOS window opens. The following entries at the flashing cursor C: \ _ provide information about the system:

ipconfig = local IP of the device, subnet mask, default gateway, etc.

ipconfig / all = name of the device (host name), physical address and
MAC address, DNS server address, name of the router, local IP of the
connected device, subnetmask, default gateway, etc.

ping local IP address = Display of the time of transmitted data packets, number of lost data packets, information on network integration.

ping Hostname = Display of the time of transmitted data packets, number of lost data packets, information on network integration.

arp -a = Internet Address, MAC Address.

nslookup domain name = domain name as byte pattern (80.152.31.143)

netstat = local address and remote address with the different port addresses for packet transmission at the default node of the router.

exit = closes the DOS window.

help = Overview of the CMD commands.

Query download and upload speed of data in the network:

http://www.speedmeter.de
(copy the address in the browser)