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What parts of the protocol data unit are covered with what part the OSI & TCP/IP models 

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In layered systems, PDU represents a unit of data specified in the protocol of a given layer, which consists of protocol control information and user data. 

  1. Data is just data
  2. Segments contain Transport header + Data
  3. Packets contain Network Header + transport header + data
  4. Frames contain Frame Header+Network Header+Transport Header+ Data+ Frame Tail
  5. and bits are bits
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What are the devices connected to the OSI & TCP/IP model? 

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 A firewall is a security equipment that uses security rules to control incoming and outgoing network traffic. It can physical or virtual. depending on its layer, it may filter:

  • packets and connections (L4)
  • Application and protocols (L7)


  • Logic to forward data based on addresses between multiple networks
  • router maintain a routing table (contains directions)
  • A router often knows different paths to a destination and has to choose the best way from a to b
  • are required for wide area networks (WAN) like the internet


  • Logic to forward data based on addresses in one network or segment of a single network
  • star physical typology

Repeater and Hub

  • No logic, can be seen as a plain extension of the physical wiring
  • A Hub has a Star physical topology BUT BUS logical topology
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What is a circuit switching network? 

Circuit Switching Network: A (physical) connection is  made for a call or similar.

•Line is typically completely occupied by this one  call.

•Benefit: Simple and guaranteed bandwidth for the active call.

•Downsides: Bad network utilization and limited flexibility.

•E.g. Plain old telephone service (POTS)

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What is a packet switching network

Packet Switching: A call / or internet traffic is  transferred in small chunks (packages) which are  handled independently from each other.

•Line can easily be shared between multiple  logical connections and service types.

•Benefits: Better overall network utilization with more flexibility.

•Downside: Additional functionalities are needed to guarantee a decent service quality.

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What is the Internet Protocol?

Internet Protocol (IP): IP is designed explicitly as addressing protocol. It is mostly used with TCP. The IP addresses in packets help in routing them through different nodes in a network until it reaches the destination system. TCP/IP is the most popular protocol connecting the networks.

  • Current version: IPv4
    • 32 Bit Addresses
    • Standardized since 1981
  • Upcoming version: Ipv6
    • 128 Bit Addresses
    • Initially standardized in 1998
  • Standardized protocol that forms together with TCP and UDP the core functionality of the internet.
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What is a 32 BIT IP address?


4 times 1 Byte separated by a dot, e.g.:

•each block can have a value between 0 and 255

•allows for 2³² = 4294967296 combinations/addresses

Some of the combinations are not valid addresses


  • Reserved for internal networks (Private Address Spaces):
    • from to
    • from to
    • from to
  • Reserved for the local host / local pc:
    • from to
  • Broadcast IP
  • Loopback –
  • Etc…
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What is a 128 Bit address?


8 blocks separated by a colons, e.g.: 2001:0db8:0000:0000:0000:8a2e:0370:7334

•each block have 4 digits.

•each digit can have a value on Base16, between 0 and F. E.g. 0,1,2,3,4,5,6,7,8,9, a,b,c,d,e,f

•allows for 2128 combinations/addresses

0 at the beginning of a block may be skipped. E.g. 2001:0db8:0000:0000:0000:8a2e:0370:7334 becomes 2001:db8:0:8d3:0:8a2e:70:7344

Consecutive blocks of zeros may be skipped and replaced by two colons. E.g. 2001:db8:0:0:0:0:1428:57ab becomes 2001:db8::1428:57ab

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What is a DNS?

The Domain Name System (DNS) is the phonebook of the Internet. Humans access information online through domain names, like nytimes.com or espn.com. Web browsers interact through Internet Protocol (IP) addresses. DNS translates domain names to IP addresses so browsers can load Internet resources.

Each device connected to the Internet has a unique IP address which other machines use to find the device. DNS servers eliminate the need for humans to memorize IP addresses such as (in IPv4), or more complex newer alphanumeric IP addresses such as 2400:cb00:2048:1::c629:d7a2 (in IPv6).


Also possible: IP to Domain resolution ( ”reverse DNS” )

e.g. à fhnw.ch