Intro to VLAN Trunking
VLANs and Trunks for Beginners - Part 2
VLANs and Trunks for Beginners - Part 3
Spanning Tree Introduction: STP, RSTP, and MSTP
Spanning Tree Introduction
1. Spanning Tree Protocol (STP)
2. Rapid Spanning Tree Protocol (RSTP)
3. Multiple Spanning Tree Protocol (MSTP)
1. Spanning Tree Protocol (STP)
2. Rapid Spanning Tree Protocol (RSTP)
3. Multiple Spanning Tree Protocol (MSTP)
IP subnetting tips and tricks
An IP address has two components, the network address and the host address. A subnet mask separates the IP address into the network and host addresses (<network><host>). Subnetting further divides the host part of an IP address into a subnet and host address (<network><subnet><host>). It is called a subnet mask because it is used to identify network address of an IP address by perfoming bitwise AND operation on the netmask.
A Subnet mask is a 32-bit number that masks an IP address, and divides the IP address into network address and host address. Subnet Mask is made by setting network bits to all "1"s and setting host bits to all "0"s. Within a given network, two host addresses are reserved for special purpose. The "0" address is assigned a network address and "255" is assigned to a broadcast address, and they cannot be assigned to a host.
IP subnetting tips and tricks - part 1
IP subnetting tips and tricks - part 2
IP subnetting tips and tricks - part 3
IP subnetting tips and tricks - part 4
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DANSCOURSES
IP Addresses and Subnets
This page will give you a basic understanding of the structure of IP addresses and subnets at Cornell.
- What Are IP Addresses and How Are They Used?
- IP Addressing Space
- How Does Subnetting Work?
- Understanding Static vs. Dynamic Addressing
- Host Registration
- IPv4 Global Address Blocks Owned and Managed by Cornell
What Are IP Addresses and How Are They Used?
IP (Internet Protocol) addresses are used to identify hosts on the campus network that in turn ties into the Internet, a global network. A networked computer must have an IP address assigned to the computer to be recognized as part of the network.
IP addresses are constructed according to a set of specific rules so that hosts on any part of the Internet can communicate with each other. This document describes IP addresses only as they apply to Cornell's campus network. (If you want to know more about Internet addressing, refer toInternetworking with TCP/IP: Principles, Protocols, and Architecture by Douglas Comer, Prentice Hall).
An IP address consists of a 32-bit binary number, which is typically presented as four decimal numbers (one for each 8-bit byte) separated by decimal points. For example, 128.253.21.58.
Internet addresses at Cornell have three parts:
Network Address
Cornell has several addresses for its backbone networks. The addresses are 128.84.0.0, 128.253.0.0, 132.236.0.0, 192.35.82.0, 192.122.235.0, and 192.122.236.0. These addresses are assigned to Cornell. Cornell cannot change the first two parts of each address, but is free to use the last two parts in any way it chooses in order to identify Local Area Networks (subnets) and hosts that are connected to the campus Internet.
The subnet address is the address given to your Local Area Network (LAN). Cornell's system provides for 254 LANs connected to each of the main networks. So, for example, if your LAN is identified on the network as 128.253.0.0, a possible subnet addresses (or LAN address) might be 128.253.21.0. The third number, 21, identifies the subnet.
The host address is the address given to the workstation, other computer, or device that is connected to the LAN. Cornell's system provides for 256 host addresses on each LAN. So, for example, if your host is identified on the LAN as 128.253.21.0 a possible host address is 128.253.21.58. The last number, 58, identifies the host. Not all 256 numbers are available as host addresses on any given LAN. Zero (0) and 255 are reserved for broadcast purposes. Hosts are set up to "grab" any message marked with their own address or a broadcast address; for example, if your host address is 128.253.21.58 and it "sees" a message addressed to 128.253.21.255, it will grab the message. In this way, hosts can send messages to large groups without having to know each address on their LAN.
One (1) is reserved for the gateway/router that sits between the LAN and next network level. The numbers 2-5 are reserved by CIT for diagnostic and management use.
IP Addressing Space
This addressing scheme has worked well for Cornell, but it has some limitations:
- Each of Cornell's fiber backbones can have no more than 256 LANs attached to them.
- Each LAN can have no more than 256 (249 if reserved addresses are taken into account) hosts. Most LANs are constructed with far fewer than the maximum number of hosts addresses available.
- Ethernet LAN performance is reduced with a large number (100 or more) of connections. Performance is most affected by how people are using the LAN: a small number of heavy users can bog down the performance of any LAN. Therefore, the limitations on the number of host addresses hasn't been and isn't expected to be a problem for most LANs at Cornell.
Classless Inter-Domain Routing (CIDR) helps us bypass limitations on the number of IP addresses available on our network.
How Does Subnetting Work?
Each subnet address at Cornell is assigned a "subnet mask." A subnet mask defines how many bits are used for the network address and how many for the host address.
The subnet mask address is 255.255.255.0, and it currently is the same for all LANs. If you convert the subnet mask address to its binary form, it looks like this:
Subnet mask: 11111111 11111111 11111111 00000000
If you convert our example host address (128.253.21.58) to its binary form, it looks like this:
Host address: 10000000 11111101 00010101 00111010
Together they look like this:
Subnet mask: 11111111 11111111 11111111 00000000Host address: 10000000 11111101 00010101 00111010
The subnet mask when shown this way, as an overlay on the host address, essentially tells the computer which part of the IP address is a network address and which part is a host address. Everything in the host address that corresponds to a 1 in the subnet mask is a network address and everything in the host address that corresponds to a 0 in the subnet mask is a host address.
Understanding Static vs. Dynamic Addressing
If you use static addressing on your network, this means you assign each host a permanent IP address. If you use dynamic addressing, the hosts use any available address within a range you specify. The information below explains some of the advantages and disadvantages of static and dynamic addressing.
Before you begin reconfiguring your applications, you should decide which scheme you plan to use: static, dynamic, or a combination. CIT recommends that you use static addressing; it helps you, as the network administrator, keep track of machines and figure out which one is causing problems. Some network applications require static addressing.
If you want to consider dynamic addressing because it is easier to set up, CIT advises that you limit the range for dynamically assigned addresses to start at 21, thus leaving 6-20 reserved for hosts that need fixed addresses because they will offer IP services. If you think you will have more than 15 IP server hosts, you should raise the start point for dynamically assigned addresses.
Host Registration
Network administrators are required to register all devices on their networks (desktop workstations, servers, printers, etc.). See How to Comply with Network Registration Policy for more information.
IPv4 Global Address Blocks Owned and Managed by Cornell
Cornell owns and manages the following publicly routable IPv4 global address blocks:
- 128.84.0.0/16
- 128.253.0.0/16
- 132.236.0.0/16
- 192.35.82.0/24
- 192.122.235.0/24
- 192.122.236.0/24
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The 7 Layers of the OSI Model
The OSI, or Open System Interconnection, model defines a networking framework to implement protocols in seven layers. Control is passed from one layer to the next, starting at the application layer in one station, and proceeding to the bottom layer, over the channel to the next station and back up the hierarchy.
There's really nothing to the OSI model. In fact, it's not even tangible. The OSI model doesn't do any functions in the networking process, It is a conceptual framework so we can better understand complex interactions that are happening. The OSI model takes the task of internetworking and divides that up into what is referred to as a vertical stack that consists of the following layers:
Physical (Layer 1)
This layer conveys the bit stream - electrical impulse, light or radio signal -- through the network at the electrical and mechanical level. It provides the hardware means of sending and receiving data on a carrier, including defining cables, cards and physical aspects. Fast Ethernet, RS232, and ATM are protocols with physical layer components.
- Layer 1 Physical examples include Ethernet, FDDI, B8ZS, V.35, V.24, RJ45.
Data Link (Layer 2)
At this layer, data packets are encoded and decoded into bits. It furnishes transmission protocol knowledge and management and handles errors in the physical layer, flow control and frame synchronization. The data link layer is divided into two sub layers: The Media Access Control (MAC) layer and the Logical Link Control (LLC) layer. The MAC sub layer controls how a computer on the network gains access to the data and permission to transmit it. The LLC layer controls frame synchronization, flow control and error checking.
- Layer 2 Data Link examples include PPP, FDDI, ATM, IEEE 802.5/ 802.2, IEEE 802.3/802.2, HDLC, Frame Relay,
Network (Layer 3)
This layer provides switching and routing technologies, creating logical paths, known as virtual circuits, for transmitting data from node to node. Routing and forwarding are functions of this layer, as well as addressing,internetworking, error handling, congestion control and packet sequencing.
- Layer 3 Network examples include AppleTalk DDP, IP, IPX.
Transport (Layer 4)
This layer provides transparent transfer of data between end systems, or hosts, and is responsible for end-to-end error recovery and flow control. It ensures complete data transfer.
- Layer 4 Transport examples include SPX, TCP, UDP.
Session (Layer 5)
This layer establishes, manages and terminates connections between applications. The session layer sets up, coordinates, and terminates conversations, exchanges, and dialogues between the applications at each end. It deals with session and connection coordination.
- Layer 5 Session examples include NFS, NetBios names, RPC, SQL.
Presentation (Layer 6)
This layer provides independence from differences in data representation (e.g., encryption) by translating from application to network format, and vice versa. The presentation layer works to transform data into the form that the application layer can accept. This layer formats and encrypts data to be sent across a network, providing freedom from compatibility problems. It is sometimes called the syntax layer.
- Layer 6 Presentation examples include encryption, ASCII, EBCDIC, TIFF, GIF, PICT, JPEG, MPEG, MIDI.
Application (Layer 7)
This layer supports application and end-user processes. Communication partners are identified, quality of service is identified, user authentication and privacy are considered, and any constraints on data syntax are identified. Everything at this layer is application-specific. This layer provides application services for file transfers, e-mail, and other network software services. Telnet and FTP are applications that exist entirely in the application level. Tiered application architectures are part of this layer.
- Layer 7 Application examples include WWW browsers, NFS, SNMP, Telnet, HTTP, FTP
TCP/IP - Transmission Control Protocol/Internet Protocol
Short for Transmission Control Protocol/Internet Protocol, TCP/IP also commonly abbreviated as TCP was developed in 1978 and driven by Bob Kahn andVint Cerf. Today, TCP/IP is a language governing communications among all computers on the Internet.
TCP/IP is two separate protocols, TCP and IP, that are used together. The Internet Protocol standard dictates how packets of information are sent out over networks. IP has a packet-addressing method that lets any computer on the Internet forward a packet to another computer that is a step (or more) closer to the packet's recipient. The Transmission Control Protocol ensures the reliability of data transmission across Internet connected networks. TCP checks packets for errors and submits requests for re-transmissions if errors are found.
Features of TCP/IP
The industry was using TCP/IP around 35 years. It is a tested and proved protocol suit.
1) Multi-Vendor Support. TCP/IP is implemented by many hardware and software vendors. It is an industry standard and not limited to any specific vendor.
2) Interoperability. Today we can work in a heterogeneous network because of TCP/IP. A user who is sitting on a Windows box can download files from a Linux machine, because both Operating Systems support TCP/IP. TCP/IP eliminates the cross-platform boundaries.
3) Logical Addressing. Every network adapter has a globally unique and permanent physical address, which is known as MAC address (or hardware address). The physical address is burnt into the card while manufacturing. Low-lying hardware-conscious protocols on a LAN deliver data packets using the adapter's physical address. The network adapter of each computer listens to every transmission on the local network to determine whether a message is addressed to its own physical address.
For a small LAN, this will work well. But when your computer is connected to a big network like internet, it may need to listen to millions of transmissions per second. This may cause your network connection to stop functioning.
To avoid this, network administrators often segment (divide) big networks into smaller networks using devices such as routers to reduce network traffic, so that the unwanted data traffic from one network may not create problem in another network. A network can be again subdivided into smaller subnets so that a message can travel efficiently from its source to the destination. TCP/IP has a robust subnetting capability achieved using logical addressing. A logical address is an address configured through the network software. The logical addressing system used in TCP/IP protocol suit is known as IP address.
4) Routability. A router is a network infrastructure device which can read logical addressing information and direct data across the network to its destination.TCP/IP is a routable protocol, which means the TCP/IP data packets can be moved from one network segment to another.
5) Name Resolution. IP addresses are designed for the computers and it is difficult for humans to remember many IP addresses. TCP/IP allows us to use human-friendly names, which are very easy to remember (Ex. www.omnisecu.com). Name Resolutions servers (DNS Servers) are used to resolve a human readable name (also known as Fully Qualified Domain Names (FQDN)) to an IP address and vice versa.
6) Error Control and Flow Control.The TCP/IP protocol has features that ensure the reliable delivery of data from source computer to the destination computer. TCP (Transmisssion Control Protocol) defines many of these error-checking, flow-control, and acknowledgement functions.
7) Multiplexing/De-multiplexing. Multiplexing means accepting data from different applications and directing that data to different applications listening on different receiving computers. On the receiving side the data need to be directed to the correct application, for that data was meant for. This is called De-multiplexing. We can run many network applications on the same computer. By using logical channels called ports, TCP/IP provides means for delivering packets to the correct application. In TCP/IP, ports are identified by using TCP or UDP port numbers.
TCP/IP History
The predecessor of today’s Internet was ARPAnet, created by the Advanced Research Projects Agency (ARPA) and launched in 1969 during "Cold War". The extreme distrust that existed between USA and USSR (Soviet Union) was almost on the verge of a nuclear war during that time. "Cold War" was the term used to describe the relationship between USA and USSR during period 1945 to 1990. ARPAnet was created in response to the potential threat of nuclear attack from the Soviet Union. One of ARPA’s primary goals was to design a fault-tolerant network that would enable U.S. military leaders to stay in contact in case of nuclear war.
The protocol used on the ARPAnet was called Network Control Protocol (NCP). As the ARPAnet grew, however, a new protocol was needed because NCP was not able to fulfil all the needs of a larger network.
In 1974 Vint Cerf and Bob Kahn, published a paper “A Protocol for Packet Network Interconnection.” This paper describes the Transmission Control Protocol (TCP), which eventually replaced NCP.
By 1978, testing and further development of this language led to a new suite of protocols called Transmission Control Protocol/Internet Protocol (TCP/IP). In 1982, it was decided that TCP/IP would replace NCP as the standard language of the ARPAnet. RFC 801 describes how and why the transition from NCP to TCP was to take place. On January 1, 1983, ARPAnet switched over to TCP/IP, and the network continued to grow very fast.
ARPAnet ceased to exist in 1990. The Internet has since grown from ARPAnet’s roots, and TCP/IP has evolved to meet the changing requirements of the Internet.
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