Networks 101 PDF

Networks 101 Basics & Terminology Layers Analogy: Layers in the real world Application 2 TCP/IP Architecture TCP/IP class Application layer Ninja Gives programs access to the network. Several protocols for several programs are used Transport layer Connection establishment , error free data t...

Networks 101 Basics & Terminology Layers Analogy: Layers in the real world Application 2 TCP/IP Architecture TCP/IP class Application layer Ninja Gives programs access to the network. Several protocols for several programs are used Transport layer Connection establishment , error free data transport Internet layer Addressing and path finding in the network Network layer Is packing the data into frames and sends it to the hardware layer 3 Layers Parts of a layer of the TCP/IP class belong to • The protocol Defines the method of communication between two machines. Type and sequenz of the data Example: RFC 821 S: MAIL FROM:<[email protected]> R: 250 OK S: RCPT TO:<[email protected]> R: 250 OK S: DATA R: 354 Start mail input; end with <CRLF>.<CRLF> S: Hello Sales Team! S: <CRLF>.<CRLF> R: 250 OK • The implementation (The practical programming) How does a system / a program react, if the differently in the protocol defined commands arrive. 4 The MAC-address MAC-address (Media-Access-Control) • The MAC address is part of the network layer. • It defines the network card and is the address on the lowest level. • Syntax: 00-CF-A7-34-0B-13 (or00:CF:A7:34:0B:13) • It is directly bond to the hardware (ethernet card). 5 TCP/IP architecture IP, TCP and UDP UDP TCP Uses the unreliable IP service and sends it to the application layer. Establishes a logical, reliable connection between sender and receiver. Pack it, send it, forget it. Enhances IP by the possibility to address applications via ports. Complex Easy and simple. IP Allows the (unreliable) connectionless transport of data packages trough the internet. 6 IP - address IP - address ➔ Address in the network • In Analog to the postal mail address the IP address defines the receiver of a data package. • Every data package gets an IP address attached. Byte 1 Byte 2 Byte 3 Byte 4 87. 230. 73. 24. 01010111 11100110 01001001 00011000 7 Network prefix and host identifier Consistence of an IP address • An IP – address can be devided into two parts: • Network prefix (equals the area code of a telephone number) • Host identifier (equals the dial number ) • Example: 160.57.2.10 • Computers are in the same IP network, if the network prefix of their address is the same. Only if this is given both systems are able to communicate! 8 Network prefix and host identifier Two networks • Network prefix and host identifier can have a different length (later more) 9 Network prefix and host identifier - Classes How large is the network prefix? • Different sizes are defined by the the IP address range. • The firste byte gives the information how large the network is. Class First Byte Network-ID (black) Number of networks Number of hosts A 1-126 xxx.xxx.xxx.xxx 126 16.777.214 Apple, HP, IBM B 128-191 xxx.xxx.xxx.xxx 16384 65534 Microsoft, Exxon C 192-223 xxx.xxx.xxx.xxx 2.097.152 254 10 Network prefix and host identifier Subnetting Reasons for a further separation • Due to performance reasons in a network with so much hosts it is reasonable to split bigger networks into smaller pieces. • Due to the shortage of public IP addresses it is reasonable to split. I.e. a ISP can supply a company with 8 different public IP addresses. 11 Network prefix and host identifier Subnetting The subnet mask • The subnet mask belongs to the IP configuration. • The subnet mask determines what part belongs to the network or to the host. IP - address 192.168.10.25 11000000 10101000 00001010 00011001 Subnet mask 255.255.255.0 11111111 11111111 11111111 00000000 AND = Network prefix 192.168.10.0 11000000 10101000 00001010 00000000 12 Routing Routing ▪ In the same LAN a host receives all packages and will only use them, if addressed to himself (or broadcasted to all). ▪ If the destination is not part of the LAN the connection has to be routed. 13 Routing / Router ▪ Always has 2 IP addresses ▪ Will be set on the host as the default gateway (standard router) 14 Routing Data package Yes Question: Is the data package for me? Processing No Yes Forward it to a subnet or drop the package Question: Is the data package for my subnet? No Yes Question: Is the route to the receiver of my data package known? Forward to the known route No Yes Question: Do I know a standard gateway where I can send the data package to? Forward to the standard gateway No Error message! 15 Public vs. Private IP - address Public IP addresses • Will be routed in the internet. Are available form the outside. • Will be assigned by a central service. • You can send a ping to receive the public IP address of a host 16 Public vs. Private IP address Private IP address • In principle you can use any IP address in a private network • There are some „officially“ defined IP address ranges Address ranges for private IP addresses Class 10.0.0.0 – 10.255.255.255 A 172.16.0.0 – 172.31.255.255 B 192.168.0.0 – 192.168.255.255 C 17 Public vs. Private IP - address How to get the private IP address • You can get your own private IP address(es) by using the IPconfig command (available in Windows) 18 Routing Specify the route • You can follow the route to a host by using the tracert command (only available in windows). 19 Network Address Translation (NAT) Because of the shortage of public IP addresses not every computer has it´s own public IP address. WAN LAN 20 Getting your own public IP address Getting the public (external) IP address • http://www.whatismyipaddress.com 21 TCP ports • Ports allow multiple data streams to different applications. • Ports will be stated on top of the IP address to determine for what type of application the data is mentioned. Analogy: Name on the postal mail. Mail arrives at home. Proper person is identified via the name. With TCP the proper application is defined by the port. • There are special exclusive ports, but also some who are free and available. • Many applications don´t force the user to send a request with the port • UDP has also ports 22 TCP Port number Meaning 20 FTP 21 FTP 25 SMTP 80 HTTP (WWW) 443 HTTPS Proxy server ▪ A router directly transfers all network requests of the client systems. ▪ A proxy server is primarily used for the web (HTTP) and delivers all information back to the client. ▪ A proxy server buffers the data so that the request of the same website from a different user will be answered locally (faster). ▪ A proxy server works on higher layers and does not route (works not on the IP layer). 23 Firewall What is a firewall? ▪ A firewall has the function to restrict access to the network. ▪ The firewall filters the network traffic. This is mostly done via ports – what is allowed to pass trough and what not. Content filtering is also possible. ▪ The mostly used standard setting is: Outbound traffic is allowed, inbound not. Attention: Outbound means „initially outgoing“. The incoming connection reply is allowed. ▪ Pure firewalls are very rare. Many devices combine router, firewall, NAT-router or DSL modem. 24 Firewall 25 Domain Name System (DNS) ▪ IP addresses are hard to read / remember for a human being ▪ The DNS is a index service which assigns a domain name to an IP address. Similar to a telephone book. ▪ Server who provide this type of service are called name server. (Servers are programms or hardware who run a special program. Or DC i.e. is a name server, but also has a lot of other functions: Mail server, SQL-Server, etc.) 26 Domain 27 Dynamic Host Configuration Protocol - DHCP ▪ The process of assigning IP addresses can be very annoying. ▪ Question: Which IP address is available? ▪ Automating via DHCP – the DHCP does the service… 28 Network Architecture / Topology 29 Demilitarized Zone - DMZ 30 Terminal Server Terminal Server Thin Client Mainframe? 31 Any questions?