Network Basics GRAPHISOFT. for connecting to a BIM Server (version 1.0)

Transcription

1 for connecting to a BIM Server GRAPHISOFT 2009 (version 1.0)

2 Basic Vocabulary...3 Local Area Networks...5 Examples of Local Area Networks...5 Example 1: LAN of two computers without any other network devices...5 Example 2: LAN with more than 2 computers and a connecting device...6 Example 3: LAN with more than 2 computers and a router...6 Example 4: LAN with more than 2 computers, a router and a connecting device...7 Network Devices within a Local Area Network...8 IP Address...9 Subnet Mask...10 Local Area Network with Sub networks...11 IP Address in a LAN with sub networks...11 Subnet Mask in a LAN with sub networks...12 An example of a network before and after using subnetting...12 DHCP server...14 Typical characteristics of a Small Office LAN...14 IP Address on the Internet (Public Address)...15 Network Address Translation NAT...16 Port Address Translation (PAT)...18 AC client connecting to a BIM server from the same LAN...18 AC client connecting to a BIM server from outside of the office LAN

3 Basic Vocabulary Computer network: is a group of interconnected computers. It allows computers to communicate with each other and to share resources and information. Server application: An application that receives requests from applications and offers services as responses to these requests. Server applications can be run both on server or client computers. Client application: An application that addresses requests to a server application and gets services from the server application based on these requests. Client applications can be run both on server or client computers. Server: offers services to multiple clients, each client in general will need to prove who it is ("authentication") and will need to have rights to the requested service ("authorization). Client: A computer that uses the services of a server. Host: Any computer within a network. LAN: Local Area Network, for example your office s network. IP Address: A number that uniquely identifies every host on an IP network. A computer will have as many IP addresses as it has installed network cards. Static IP Address: IP address that is assigned to a computer to be its permanent address. Dynamic IP Address: IP address that is assigned to a computer for some other specified amount of time. Public IP Address: IP address assigned to any computer directly connected to the Internet. A Public IP address is unique on the Internet. Private IP Address: IP address assigned to computers that are not directly connected to the Internet. A private IP address is unique only in the network it is directly connected to. Internet Protocol Suite: Commonly known as TCP/IP set of communication protocols used for The Internet and other similar networks. o The Transmission Control Protocol (TCP) provides ordered delivery of packets of data (called datagrams) from a program on one computer to another program on another computer. The TCP protocol is used within Web browsers, , and file transfer among other things. Typically its management tasks, include TCP datagram size, the rate at which datagrams are exchanged, and the regulation of network traffic to prevent congestion. o The Internet Protocol (IP) is responsible for splitting up the TCP packets into smaller parts and forwarding these parts to the recipient. 3

4 Router: Responsible for finding an appropriate path through the network. Firewall: A program that blocks unwanted/unauthorized or dangerous network traffic from proceeding from one network to the other. Hub : Is used to connect machines and often used to enhance the strength of the signal to overcome the impedance of the cabling. Messages are not examined. Bridge, Switch: Are Intelligent Hubs, they are meant to examine traffic to avoid forwarding messages to other non-concerned computers. Modem: In this document we use the word modem for Cable Modems and ADSL Modems. These are devices that make connection to Internet possible via CATV cables or Public Phone lines. They transform data coming via signals on these media to digital data and vice versa. DHCP-Server: Server application (service) distributing unique IP addresses. A DHCP service can run on any computer on the network, but usually they run on the Server Computer or one of the Server Computers in a LAN. MAC Address: Media Access Control address is a unique identifier assigned to most network adapters or network interface cards (NICs) by the manufacturer for identification. The standard (IEEE 802) format for printing MAC-48 addresses in human-friendly form is six groups of two hexadecimal digits, separated by hyphens (-) or colons (:), in transmission order, e.g ab, 01:23:45:67:89:ab Domain name: An identification label that defines a realm of administrative autonomy, authority, or control in the Internet, based on the Domain Name System (DNS). A regular user meets domain names much more frequently than IP addresses even though the basis of communication on the Internet is IP address. An important purpose of domain names is to provide easily recognizable and memorizable names to numerically addressed Internet resources. DNS-Server: Domain Name System servers, are used to translate a hostname or a domain name (for example, ) to its corresponding binary identifier (the IP address ), or vice versa. Port: A number chosen for or by a network application. This number is used to route packets to the appropriate network application of more network applications running on one single computer. 4

5 Local Area Networks In this document we only discuss computer networks using Ethernet and WiFi technology. An Ethernet Network is a LAN or a part of a LAN where computers are connected between each-other through Ethernet cables and which are using the communication protocol defined by the IEEE standard. A WiFi Network is a LAN or a part of a LAN where computers are connected between each-other through short range radio wave and which are using the communication protocol defined by the IEEE standard. In LAN s Ethernet and WiFi technology can be inter-mixed. The computers connected by either of the technologies can be regarded as part of the same LAN. Examples of Local Area Networks Example 1: LAN of two computers without any other network devices Figure 1. Example 1 of LAN The computers are connected through a cross-over Ethernet cable. This is needed because there no Hub, Bridge, Switch or Router is used for this network. Regular Ethernet cable can be used between a computer and one of the four mentioned network devices. Connection of this LAN to another LAN can be made if one of the computers has another network card or WiFi card installed. Connection to the Internet can be made via a Modem connected to one of the computers. 5

6 Example 2: LAN with more than 2 computers and a connecting device Figure 2. Example 2 of LAN Computers are connected through a Hub, Bridge or Switch. Connection of one computer to another LAN at the same time can be made if one of the computers has another network card or WiFi card installed. Connection to the Internet can be made via a Modem connected to one of the computers. Example 3: LAN with more than 2 computers and a router Figure 3. Example 3 of LAN Computers are connected through a Router. Connection of this LAN to another LAN or to the Internet can be made through the appropriate interface of the router. 6

7 Example 4: LAN with more than 2 computers, a router and a connecting device Figure 4. Example 4 of LAN The computers are connected through a Hub, Bridge or Switch. Connection to the Internet can be made via the Router itself connected to the Hub, Bridge or Switch. 7

8 Network Devices within a Local Area Network In a simple LAN all network devices are connected to each other: Figure 5. - Devices within a LAN 8

9 IP Address In a Network to every Network Card an IP Address has to be assigned. An IP address is a series of 0-s and 1-s grouped in 4 octets (octet means 8 digits). An example for this is: For making the IP address more human readable 8 digits are shown as their decimal equivalent. This way the previous IP address will be shown as For Private IP Addresses the following three ranges of addresses are recommended: Figure 6. Private IP addresses (a) In a LAN only one of the three ranges can be used at once. Figure 7. Private IP addresses (b) In a LAN the network ID part has to be the same for all the devices while the host ID part has to be different for all the devices. 9

10 Subnet Mask The subnet Mask indicates which part of an IP address is regarded as a Network ID and which part is regarded as a Host ID. The length of the Host ID defines implicitly the maximum number of Hosts in a LAN. The Network ID is the part of the IP address that identifies the Network. The Host ID is the part of the IP address which identifies the particular host in the network Bits of a Network ID are represented by a 1 in the mask. Bits of a Host ID appear as a 0 in the mask. Figure 8. Subnet Mask (a) 10

11 Local Area Network with Sub-networks In larger offices some parts of the Network might be organized in sub-networks. By using sub-networks different groups of computers can be securely separated. Some data traffic will not be able to cross the boundaries of sub-networks according to the settings made in the appropriate switch or router. The success of client-server based functionality might depend on such settings. Figure 9. Sub-networks IP Address in a LAN with sub-networks In LAN s with subnets the subnet Mask is much more variable. In a LAN the mask implicitly defines and the maximum number of subnets and the maximum number of hosts in a subnet. Figure 10. IP Address ans Sub-networks 11

12 Subnet Mask in a LAN with sub-networks The series of 1 s is longer in the subnet mask for the subnet than the original subnet mask. The extra bits make possible the identification of the subnet in the IP address. Figure 11. Subnet Mask (b) An example of a network before and after using subnetting The network without subnetting has been assigned a network ID of Class B address In the second network, the first four bits of the host ID are used to divide the network into two small networks, identified as subnets 16 and 32. Both networks still appear to be a single network identified as For example, the out- side world considers the device at to belong to the network. A packet Figure 12. Before and After Sub-netting 12

13 sent to this device will be delivered to the router at The router then considers the subnet portion of the host ID to decide whether to route the packet to subnet 16 or subnet 32. Figure 13. Before and After Sub-netting (Network ID s and Masks) 13

14 DHCP server Every host on a TCP/IP network must have a unique IP address. This is done by a DHCP server. When a new host comes online, it must be assigned an IP address within the correct range of addresses for the subnet. The DHCP server automatically configures the IP address for every host on a network, assuring that each host has a valid unique IP address. The request from the client for an IP address and the answer with the given IP address is transferred using the DHCP (Dynamic Host Configuration Protocol). The DHCP server automatically reconfigures IP addresses as hosts come and go. Figure 14. DHCP server distributing unique IP addresses to hosts Typical characteristics of a Small Office LAN Sub-netting is not usual. The subnet mask is (C address class) which also means that a maximum of 254 hosts can be connected. The router that connects to the Internet is probably also acting as a DHCP and DNS server. 14

15 IP Address on the Internet (Public Address) When the Internet was young, all computers received an Internet address. As time progressed it was clear that the address range would slowly be exhausted, so a new scheme to limit the use of IP addresses was needed. So arose the concept of public and private IP addresses. Public addresses would be issued by a central authority and any company could use as many private addresses as they wanted. Figure 15. Private and Public IP Addresses 15

16 Network Address Translation - NAT Network Address translation is the process of modifying network address information in datagram packet headers while in transit across a traffic routing device for the purpose of remapping a given address space into another. The router must use a globally unique IP to represent the host to the Internet. As packets cross the router, it translates the private IP address to the public IP address and vice versa. Figure 16. Network Address Translation Let s see a short scenario on how NAT works: A host whose private address is sends a request to , which happens to be The NAT device changes the source IP address of the packet to , the Public IP address of the router. That way, Google will send its reply back to the router. The NAT records that sent a request to Now another host, at address , sends a request to , which happens to be The NAT device changes the source of this request to so Microsoft will reply to the router. The NAT records that sent a request to A few seconds later, the router receives a reply from The destination address in the reply is , the public address of the router. To determine to whom to forward the reply, the router checks its records to see who is waiting for a reply from

17 It discovers that is waiting for that reply, so it changes the destination address to and sends the packet on 17

18 Port Address Translation (PAT) Port Address Translation is a feature of a network device that translates TCP communications made between hosts on a private network and hosts on a public network. It allows a single public IP address to be used by many hosts on a private network based on ports. For presenting the way PAT works we will use an example specific to ArchiCAD Teamwork 2. Figure 17. Port Address Translation Let s see a scenario of a PAT. The red arrows represent requests and answers going to and coming from DNS servers. The black arrows represent data traffic between an ArchiCAD client and a BIM server. AC client connecting to a BIM server from the same LAN ArchiCAD sends a request to the local DNS server asking the IP address assigned to the domain name bim-server.company.com. The local DNS server answers it with a Private IP address. In this case it is ArchiCAD sends a packet to and it also specifies port 9991 as the port for communication. Since the server computer is available on the Local Network it immediately receives the packet and based on the port the Operating System of the server 18

19 computer forwards the packet to the desired server application. In this case this is the BIM server application. The BIM server application reads the packet, it identifies the source IP address of the sender computer and the answering packet will be sent to this IP address. AC client connecting to a BIM server from outside of the office LAN ArchiCAD sends a request to a DNS server on the Internet which knows the IP address assigned to the domain name bim-server.company.com. Finding the DNS server which really knows this information is a bit more complex but in this case it is enough for understanding the process. The DNS server responds it with a Public IP Address. In this case it is This is by the way the Public IP Address of the Router which connects the office LAN to the Internet. Then the ArchiCAD client send its packet to the Public Address The packet reaches company router. The router checks the packet, identifies the source IP address and checks if there are any restrictions that apply for packets like this. If there are no restrictions then based on the port address it substitutes the target IP address of this packet with the local IP address of the BIM server, which in this case is This is the Port Address Translation phase. It sends the packet to the Private LAN. If the server computer is available on the Local Network, it receives the packet, and based on the port the Operating System of the server computer, forwards the packet to the BIM server application. The BIM server application reads the packet, it identifies the source IP address of the sender computer and the answering packet will be sent to this IP address. But before the outgoing packet can reach the Internet it first goes to the router. The router again checks the packet, it identifies the source IP address and checks if there are any restrictions that apply for packets like this. If there are no restrictions then based on the port address it substitutes the source IP address of this packet with the public IP address assigned to the router, which in this case is This is the Port Address Translation phase. It sends the packet to the Public IP Address of the AC client through the Internet. 19