Karteikarten
Network Basics
Karten in diesem Stapel (14)
- 1Explain the OSI modelThe Open Systems Interconnection model (OSI model) is a conceptual model that characterises and standardises the communication functions of a telecommunication or computing system without regard to its underlying internal structure and technology. Its goal is the interoperability of diverse communication systems with standard communication protocols. The model partitions a communication system into abstraction layers. The original version of the model had seven layers.
A layer serves the layer above it and is served by the layer below it.
The layers are:
- Physical Symbol Transmission and reception of raw bit streams over a physical medium.
- Data link Frame Reliable transmission of data frames between two nodes connected by a physical layer.
- Network Packet Structuring and managing a multi-node network, including addressing, routing and traffic control.
- Transport Segment, Datagram Reliable transmission of data segments between points on a network, including segmentation, acknowledgement and multiplexing.
- Session Managing communication sessions, i.e. continuous exchange o - 2What is the advantage of the layered architecture?- It has all flexibility to adopt features of other protocols.
- It allows multiple-vendor development through the standardization of network components.
- It allows various types of network hardware and software to communicate.
- It prevents changes in one OSI layer from affecting other layers to accelerate development. - 3Name two services for each, TCP and UDPTCP services:
- Process-to-Process Communication – TCP provides process to process communication, i.e, the transfer of data takes place between individual processes executing on end systems. This is done using port numbers or port addresses. Port numbers are 16 bit long that help identify which process is sending or receiving data on a host.
- Stream oriented – This means that the data is sent and received as a stream of bytes(unlike UDP or IP that divides the bits into datagrams or packets). However, the network layer, that provides service for the TCP, sends packets of information not streams of bytes. Hence, TCP groups a number of bytes together into a segment and adds a header to each of these segments and then delivers these segments to the network layer. At the network layer, each of these segments are encapsulated in an IP packet for transmission. The TCP header has information that is required for control purpose which will be discussed along with the segment structure.
- Full duplex service – This means that the communication can take place in both directions at the same - 4What is MTU?A maximum transmission unit (MTU) is the largest size of packet or frame, specified in octets (eight-bit bytes), that can be sent in a packet- or frame-based network such as the Internet. The Internet's Transmission Control Protocol (TCP) uses the MTU to determine the maximum size of each packet in any transmission. Too large MTU size may mean retransmissions if the packet encounters a router that can't handle that large a packet. Too small an MTU size means relatively more header overhead and more acknowledgements that have to be sent and handled. Most computer operating systems provide a default MTU value that is suitable for most users. In general, Internet users should follow the advice of their Internet service provider (ISP) about whether to change the default value and what to change it to.
- 5What is the purpose of an IP address?An Internet Protocol address (IP address) is a numerical label assigned to each device connected to a computer network that uses the Internet Protocol for communication. An IP address serves two main functions: host or network interface identification and location addressing.
Internet Protocol version 4 (IPv4) defines an IP address as a 32-bit number. However, because of the growth of the Internet and the depletion of available IPv4 addresses, a new version of IP (IPv6), using 128 bits for the IP address. - 6What is the purpose of private IP addresses (RFC 1918)?In the Internet addressing architecture, a private network is a network that uses private IP address space. Both, the IPv4 and the IPv6 specifications define private addressing ranges. These addresses are commonly used for local area networks (LANs) in residential, office, and enterprise environments. Private IP address spaces were originally defined in an effort to delay IPv4 address exhaustion.
Private network addresses are not allocated to any specific organisation and anyone may use these addresses without approval from a regional Internet registry. However, IP packets addressed from them cannot be routed through the public Internet. - 7What is a collision domain? What device interconnects them?A Collision Domain is a shared medium where multiple devices try to communicate on the same medium. If two or more devices try to send at the same time a collision happens. On Ethernet CSMA/CD (Carrier Sense Multiple Access / Collision Detection) is used to prevent Collisions. Procedure is to check if there is data ready to send, if so listen on the medium if it is free start to send and also listen for collisions. If there’s a collision stop sending and initiate a jam signal to inform everyone. Increase retransmit counter, wait a random time and try sending again. Repeat.
- 8What is the purpose of a netmask?The netmask is used to specify a network size (Subnet), NetID and Broadcast address. A sub-netmask with 255.255.255.0 or as CIDR /24 describes a subnet with 256-2 usable addresses. -2 because NetID and Broadcast address.
- 9What is CIDR notation and why was it introduced?CIDR describes the same as a netmask, but in a shortener and more convenient way. /24 says that 24 bits are set for the Network and the last 8 bits are used for the hosts/clients. It's used in classless routing a lot and allows to describe different subnets in a better way and without the need to use of classes like A, B, C, or D.
- 10What is a Virtual LAN (VLAN)?A VLAN is specified in the Ethernet Frame and enables the use of different isolated networks on a managed L2 Switch. It’s possible to have multiple VLANs on one port of a device like a switch. With Tagged/Untagged marks on the ports you can either put a network directly on a port which can be used by regular clients directly (untagged). Or if you need to deploy multiple VLANs over to another Switch they can be all tagged.
- 11Name all blocks of private IP addresses10.0.0.0/8
172.16.0.0/12
192.168.0.0/16 - 12Given an IP, netmask and default gateway, you should be able tocheck if the netmask is correct
calculate the network ID and the broadcast address
calculate the number of usable IP addresses in the network - 13What happens to IP packets that are bigger than the MTU?Packets which are bigger than the MTU are fragmented or if the DF-Flag is set - are rejected with ICMP Dest-Unreachable.
- 14Why is it a bad idea to do TCP over TCP (eg. IPSEC over TCP)?Because you got everything twice what TCP does. There’s already an established connection via the first TCP connection. If there’s TCP in TCP you got twice the overhead of TCP. More Syn Ack stuff which slows down the connection even more.
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- Informatik Karteikarten am Network Basics, erstellt von Simon Perez am 05/12/2019.
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