Computer Networking
90 flashcards by MentisLibrary
OSI layers, TCP and UDP, IP addressing and subnetting, routing, DNS, and the port numbers worth memorizing. Cards are tagged with the layer they live on so the whole stack fits together.
- What are the seven OSI layers?
- Physical, Data Link, Network, Transport, Session, Presentation, Application, numbered 1 through 7 from the bottom.
- OSI layer 1: Physical
- Transmits raw bits over a medium, defining voltages, connectors, cabling, and signalling.
- OSI layer 2: Data Link
- Moves frames between directly connected nodes on the same network segment, using MAC addresses and error detection.
- OSI layer 3: Network
- Routes packets between different networks using logical addresses.
- OSI layer 4: Transport
- Provides end-to-end delivery between processes, with ports, and optionally reliability and ordering.
- OSI layer 5: Session
- Establishes, manages, and terminates conversations between applications.
- OSI layer 6: Presentation
- Translates data formats: encoding, serialization, compression, and encryption.
- OSI layer 7: Application
- The layer applications actually speak, defining the messages users and programs exchange.
- What is the TCP/IP model?
- A four-layer practical model: Link, Internet, Transport, and Application.
- What is encapsulation?
- Each layer wraps the data from the layer above with its own header as it moves down the stack.
- Frame, packet, segment, datagram
- Layer 2 units are frames, layer 3 units are packets, TCP units are segments, and UDP units are datagrams.
- What is a MAC address?
- A 48-bit hardware address burned into a network interface, written as six hex pairs.
- What is ARP?
- The Address Resolution Protocol, which finds the MAC address matching an IPv4 address on the local network.
- What is the difference between a hub, a switch, and a router?
- A hub repeats every signal to every port, a switch forwards frames only to the correct port using MAC addresses, and a router forwards packets between networks using IP addresses.
- What is a broadcast domain?
- The set of devices that will receive a layer 2 broadcast frame.
- What is a VLAN?
- A virtual LAN that logically partitions one physical switch into separate broadcast domains.
- What is an IPv4 address?
- A 32-bit identifier written as four decimal octets, identifying an interface on a network.
- What is an IPv6 address?
- A 128-bit address written as eight groups of four hex digits, with :: collapsing one run of zero groups.
- What is a subnet mask?
- A 32-bit value marking which leading bits of an address identify the network and which identify the host.
- What does a /24 give you?
- 256 total addresses, of which 254 are usable hosts after the network and broadcast addresses.
- How many usable hosts does a /26 have?
- 62. It has 6 host bits, so 64 addresses total, minus the network and broadcast addresses.
- What is the network address?
- The first address in a subnet, with all host bits zero, used to identify the subnet itself.
- What is the broadcast address?
- The last address in a subnet, with all host bits set to one, reaching every host on that subnet.
- What are the private IPv4 ranges?
- 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16, reserved by RFC 1918 for internal use.
- What is 127.0.0.1?
- The IPv4 loopback address, which always refers to the local machine.
- What is a link-local address?
- An address valid only on the local segment, self-assigned when no DHCP server answers.
- What is CIDR?
- Classless Inter-Domain Routing, which replaced fixed address classes with an explicit prefix length.
- What is subnetting?
- Splitting a larger network block into smaller ones by borrowing bits from the host portion.
- What is supernetting or route aggregation?
- Combining several contiguous prefixes into one shorter prefix to advertise fewer routes.
- What is NAT?
- Network Address Translation, which rewrites addresses so many private hosts share one public address.