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CS3102 Networks > 4: The Network Layer > Flashcards

4: The Network Layer Flashcards

1
Q

What is the network layer and its responsibilities?

A

The third layer of the reference model that is responsible for packet routing and forwarding in routers. It provides abstracted host-host logical communications.

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2
Q

What is forwarding?

A

The process by which a datagram is moved from a source device to an output device: 1 hop along a path.

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3
Q

What is routing?

A

Routing is the process by which a network as a whole determines the paths deciding how packets go from source to destination: forwarding tables are built.

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4
Q

What is the data plane?

A

The section of the architecture of a router that is responsible for determining how to deal with inbound packets on one interface: how they are forwarded out on another.

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5
Q

Whar is the control plane?

A

The section of a router’s architecture that provides the logic determining the topology of the whole network.

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6
Q

What is a per-router control plane?

A

The control plane logic is contained in all routers, who also interact in the control plane.

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7
Q

What is software-defined networking?

A

Remote servers contain the control plane logic for routers.

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8
Q

What is a network service model?

A

A list of criteria and desired properties of network functionality

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9
Q

What is the architecutre of a rotuer?

A

The design of systems used in routers and their modularisation.

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10
Q

What is decentrailised switching?

A

Using header values in inbound segments to forward them to an output port as per the forwarding table in the memory of the port they came in on.

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11
Q

What is destination-based forwarding?

A

A variant of decentralised switching in which packets are only forwarded according to their destination IP address.

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12
Q

What is generalised forwarding?

A

A variant of decentralised switching in which packets can be forwarded according to any combination of their header values.

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13
Q

What is a forwarding table?

A

A mapping of input to output interfaces used in forwarding in a router.

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14
Q

What is longest prefix matching?

A

Using the longest address prefix that matches destination address when looking for forwarding table entry for a given destination address, to minimise the number of hops to the destination after the next one.

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15
Q

What is content addressability?

A

When you store data and can retrieve it based on its content rather than its location. Useful for retrieving forwarding mappings in constant time (1 clock cycle).

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16
Q

What are switching fabrics?

A

The topology of a network using switches that defines how the switches are placed and connected, and how data are switched in the network.

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17
Q

What is a network bus?

A

A common linear half-duplex link to which all nodes are connected.

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18
Q

What is switching via memory?

A

When a traditional computer acts as a switch, taking a packet into memory, processing it to find the associated output port, then sending it there.

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19
Q

What is switching via a bus?

A

Packets directly transferred from input to output ports over a shared bus, which allows 1 packet through at a time. High traffic can cause buffering in the bus.

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20
Q

What is an interconnection network?

A

High-speed computer networks with ndoes specialised to memory and processing.

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21
Q

What is switching via interconnection network?

A

When you use the distributed processors in interconnection networks to process the packets being switched in parallel to optimise performance and overcome bus bandwidth limitations.

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22
Q

What is Input port queuing?

A

When the rate of data transmission at the output ports is smaller than lower than that in the input ports, so queues are used to buffer packets to the input ports. This causes queueing delay and loss if the input buffers overflow.

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23
Q

What is Head-of-the-Line (HOL) blocking?

A

When a slow datagram at the front of the queue at an input port in a switch prevents others in the queue from moving forward.

24
Q

What are output ports?

A

The port on a switch which packets exit from to their next hop on the path to their final destination.

25
Q

What is buffering?

A

When high traffic means packets are entered into a queue and processed one at a time, in the order they arrived.

26
Q

What is a scheduling discipline?

A

Algorithms used for distributing resources among parties which simultaneously and asynchronously request them.

27
Q

What is prioritiy scheduling?

A

A scheduling algorithm that assigns packets priorities based on some properties, then entering them in a sorted priority queue to be processed.

28
Q

What is output port queueing?

A

When you buffer multiple packets contending for access to the same output port on a switch, and the arrival rate of packets exceeds the output line speed of the port.

29
Q

What is scheduling?

A

Mechanisms for choosing which packet to send across a link next.

30
Q

What is FIFO (first in first out) scheduling?

A

Sending out packets in a buffer/queue in the same order they arrive.

31
Q

What is priority scheduling?

A

Assigning priorities to each packet, and sending the packet with the highest priority first.

32
Q

What is Round Robin (RR) scheduling?

A

Sort packets into groups called classes and cyclically output a packet from each class, internally ordered chronologically.

33
Q

What is Weighted Fair Queuing (WFQ)?

A

A variant of round-robin scheduling, in which you sort packets into groups called classes and cyclically output a packet from each class, internally ordered chronologically. In WFQ, each class also has a weight dictating how many packets it can transmit/the time it gets each turn.

34
Q

What is IP?

A

Internet Protocol is a network-layer protocol that handles the routing and addressing of packets between nodes on a computer network.

35
Q

What are routing protocols?

A

A protocol specifying how routers in a network communicate, forwarding tables in routers are built, and paths of data between two endpoint nodes are chosen.

36
Q

What is the ICMP protocol?

A

The Internet Control Message Protocol (ICMP) is a network-level protocol that seeks to assist network functionality be reporting errors and operational information, including to routers.

37
Q

What is the concept of IP fragmentation and reassembly?

A

Networks have MTUs - the largest possible link-level frames - so if these are exceeded then IP datagrams are fragmented into smaller ones and reassembled at the final destination.

38
Q

What is a link’s MTU?

A

max transfer size = the largest possible amount of data in a single link-level frame on a network

39
Q

How are fragmented IP packets reassembled?

A

With header flags that identify the original datagram, length and offset from the start of the original datagram.

40
Q

What is an IP address?

A

A 32-bit identifier for a host on the Internet that acts an interface for routers.

41
Q

What is an interface?

A

A connection between a host/router and a physical link.

42
Q

What do IP addresses point to?

A

Interfaces.

43
Q

What is a subnet?

A

A subset of a network divided by an interface on a router. The subnet part of an IP address is the high order bits; the low order bits distinguish hosts within a subnet.

44
Q

How do you identify a subnet?

A

Separate all LANs connected to different interfaces on routers.

45
Q

What is CIDR?

A

Classless InterDomain Routing is a method for identifying subents and hosts in IP addresses; the first portion of the IP address distinguishes subnets and the second hosts. A shorter subnet part leaves more bits to identify hosts, so subnet can be larger. But since less for subnet identification can have fewer of these larger networks.

46
Q

What is DHCP?

A

Dynamic Host Configuration Protocol is a network management protocol in which a server dynamically assigns IP addresses to hosts on the Internet.

47
Q

What is ICANN?

A

Internet Corporation for Assigned Names and Numbers is the body that allocates Internet domains and addresses and manages DNS.

48
Q

What is the NAT protocol?

A

Network address translation is a method of using one IP address to represent a private subnet to relieve IPv4 address exhaustion.

49
Q

Why is NAT used?

A

To relieve IP address exhaustion (in v4) and so that Internet access in a network is abstracted to one access point: nodes on the subnet in question aren’t concerned about it.

50
Q

How is NAT implemented?

A

A NAT translation table is used to map incoming datagrams to devices by port number, and outgoing datagrams replace their source IP address from that of the device to that of the router operating NAT.

51
Q

What is IPv6?

A

The sixth and most recent version of the Internet Protocol.

52
Q

How does IPv6 differ from IPv4?

A

It increases addresses to 128 bits to fix exhaustion. Further changes to the header to speed up processing and forwarding and allow QoS measures to reduce jitter, latency, and loss. Also options flags, no checksum, and a new version of ICMP (v6).

53
Q

What is the format of the IPV6 datagram?

A

The header contains priority, flow label, next header, TTL, payload length, source address, and dest address. Then payload.

54
Q

What are IPv6 options?

A

Additional non-prescriptive flags that alter how IPv6 datagrams are processed at routers or their destination host.

55
Q

What is ICMPv6?

A

The new version of ICMP in IPv6 which includes new message types and multicast group management functions.

56
Q

What is tunnelling in IPv6?

A

When you split up an IPv6 datagram and send it as the payload of an IPv4 datagram when going through IPv4 routers.

57
Q

Why aren’t people all taking up IPv6?

A

Overhead to upgrade, systems been using IPv4 for entire Intenet history, ignorance of issues, timely and costly to upgrade all low-level Internet infrastructure.

CS3102 Networks (10 decks)

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