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Network Layer > Internet Network Layer > Flashcards

Internet Network Layer Flashcards

1
Q

What are the 5 responsibilities of internet network layer services?

A
  • Move packets from an origin to a destination node
  • Avoid congestion
  • Internetworking
  • Lowest layer dealing with end to end issues such as routing
  • Must know topology to chose eligible paths
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2
Q

What is the difference between congestion and flow control?

A
  • Congestion control: looking over the whole network making sure it can carry all the traffic offered
  • Flow control: O-D point to point control, fast-senders shouldn’t overwhelm slow receivers.
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2
Q

What is the difference between congestion and flow control?

A
  • Congestion control: looking over the whole network making sure it can carry all the traffic offered
  • Flow control: O-D point to point control, fast-senders shouldn’t overwhelm slow receivers.
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3
Q

What 2 things are specific to congestion control?

A
  • Under heavy traffic the performance will eventually collapse
  • All resources (node capacity, service discipline) are involved.
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4
Q

What is a connection oriented network layer service? and describe it?

A

Virtual Circuit (VC):
- Routing decision only set up once (at the set-up time)
- Nodes know where to forward the packets

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5
Q

What is a connectionless network layer service?

A

Using Datagrams:
- No route is given in advance (each datagram knows full destination address)
- Datagrams can follow different routes

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6
Q

Pros and Cons of using datagrams oppose to connection oriented service?

A

Pro: More robust and can cope with congestion
Con: More work to setup i.e overhead

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7
Q

How does data flow in virtual circuits?

A

Data flow begins and arrives at the destination node in sequence all along same path.

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8
Q

How does data flow in datagram networks?

A

Datagram 1 , datagram 2 and 3 may not all take the same path and they may not all arrive at dest node in correct order.

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9
Q

What happens to a datagram during routing failure compared to to a VC?

A

Datagram: The datagram passing through that router is lost but not necessarily the others.
VC: All VCs that passed through the failed router are terminated

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10
Q

What state information do routers hold in datagram vs. VC subnets?

A

Datagram: Routers don’t hold state info about connections
VC: Each VC requires router table space per connection to know where to forward to according to path

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11
Q

What are the 3 different types of protocol prevalent in the internet network layer?

A
  • IP protocol
  • ICMP protocol
  • Routing protocols
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12
Q

What 3 things are involved generally in IP protocols?

A
  • Addressing conventions
  • Datagram format
  • Packet handling conventions
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13
Q

What 2 things are involved generally in ICMP protocols?

A
  • Error reporting
  • router signaling
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14
Q

What 3 things are involved generally in routing protocols?

A
  • path selection
  • forwarding tables
    -RIP, OSPF
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15
Q

What does a routing algorithm do?

A

Determines end-to-end path through network

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16
Q

What does a forwarding table in a router do?

A

Forwardring table determines local forwarding at this route

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17
Q

Where is the routing algorithm kept and where is the forwarding table kept?

A

Routing: In the control plane
Forwarding: In the data plane

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18
Q

What is the control plane?

A

How datagrams are routed on an end-to-end path from sender host to destination host

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19
Q

Where is the control plane usually implemented?

A

Remote controllers

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20
Q

What is the data plane?

A

How datagrams arriving to an input link is forwarded to the router’s output link.

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21
Q

What are the 4 components of a router’s architecture?

A
  1. Input ports
  2. Output ports
  3. high-speed switching fabric (data plane; hardware)
  4. routing processor (control plane; software)
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22
Q

What is WFQ? Describe it also

A

Weighted-Fair-Queuing:
- Generalised round robin
- Each traffic class gets weighted amount of service in each cycle

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23
Q

Can routers fragment datagrams?

A

Yes a large datagram at input can be fragmented into several smaller ones to then be reassembled at the destination

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24
Q

Can routers fragment datagrams?

A

Yes a large datagram at input can be fragmented into several smaller ones to then be reassembled at the destination

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25
Q

What does CIDR stand for?

A

Classless inter-domain routing

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26
Q

What is classless inter domain routing?

A
  • There is a subnet portion of arbitrary length
  • The address format is a.b.c.d/x where x is the number of bits in the subnet portion of the address
  • The subnet portion length can change based on num of hosts attached
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27
Q

Why is CIDR used?

A

Because it allows many users from the same network to hvae an IP address that is recognisably similar to each other - aka. they all belong to same subnetwork

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28
Q

What does DHCP stand for?

A

Dynamic host configuration protocol

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29
Q

What three things does a host need to connect to the internet? And how often do these things change

A
  • An IP address
  • A subnet mask
  • Address of nearby router
  • Each time a user moves or relocates the elements must be reconfigured
30
Q

Explain how an incoming client would be given an IP address in a network?

A
  • Incoming client sends request to join network
  • DHCP server sends back:
  • an unused IP address
  • Address of 1st hop router for client
  • Name and IP address of DNS server (domain name system)
  • The network mask
31
Q

How did networks transition from IPV4 to IPV6?

A

The entire IPV6 datagram including header fields, source/dest is held as the payload in the IPV4 datagram.

32
Q

What is tunneling?

A

When an IPV4 tunnel connects two IPV6 routers

33
Q

How does tunneling between IPV6 routers along an IPV4 tunnel work?

A
  • At IPV6 router before tunner - the datagram is encapuslated in IPV4 datagram and the Source and Destination are changed from current source (aka current IPV6 router) to the next IPV6 router after the tunnel
  • When it reaches that next IPV6 router after tunnel it uncaspulates and then can go forward to destination IPV6 routers
34
Q

What are 2 types of routing algorithms?

A

Non Adaptive
Adaptive

35
Q

What are non-adaptive algorithms? (1)

A
  • No consideration to traffic/topology changes (e.g static routing)
36
Q

What are adaptive algorithms? (4)

A

-React to changes: Topology and traffic patterns

37
Q

What are 3 types of adaptive algorithms?

A
  • Centralised (Global Information)
  • Isolated (Local Information)
  • Distributed (Global and Local iformation)
38
Q

What are 2 types of least cost algorithms for networks?

A

Distance vector
Link State algorithm

39
Q

What is the distance vector an example of?

A

Decentralised routing algorithm

40
Q

Describe the distance vector algorithm?

A
  • Calculates the least-cost-path in an ITERATIVE and DISTRIBUTED manner.
  • Each node begins with only the knowledge of the costs of its attached links
  • Then by exchanging information with neighbour nodes, nodes gradually calculateleast-cost path
41
Q

What is an example of a distance-vector algorithm?

A

Bellman-Ford’s Algorithm

42
Q

Do an example of the distance-vector algorithm

A

Remember:
- Estimate of least cost from x to y is written Dx(y)
- When you don’t have the cost of one node to another you mark its cost as INFINITY

43
Q

Describe in 3 steps the distance vector algorithm?

A
  1. Wait for a change in local link cost or a message from neighbours.
    E.G c(x,v) (cost of x to v)
  2. Update distance estimates for desired distance
  3. If distance estimates have changed - notify neighbour
44
Q

What is the link state algorithm an example of?

A

A global routing algorithm

45
Q

What is meant by a global routing algorithm?

A
  • Calculate least-cost path using complete, global knowledge about the network
  • Need mechanism to obtain this information before calculations (flooding)
  • Calculations can be performed on site or replicated at multiple sites.
  • Referred to as link-state algorithms
46
Q

Example of global routing algorithm?

A

Dijkstra’s algorithm

47
Q

What is message complexity of LS compared to DV routing algorithms?

A

LS: n nodes, E links, O(nE) messages sent
DV: exchange between neighbours only

48
Q

What is speed of convergence of LS compared to DV routing algorithm?

A

LS: O(n^2) algorithm requires O(NE) messages –> these may have oscillations
DV: may have routing loops (aka count to infinity problem)

49
Q

Comparison of robustness to router malfunction of LS and DV?

A

LS:
- Node can advertise incorrect link cost
- each node computes its own table
- Errors propagate less
DV:
- DV node can advertise incorrect path cost
- Each node table is used by others so ERRORS propagate

50
Q

How are autonomous systems connected to each other?

A

Autonomous systems can be connected to each other via EGP
- Relies on AS numbers to construct AS paths
- exterior gateway protocol routing algorithms
- These are carried out by the edge connectors

51
Q

How do autonomous systems route internally?

A

Using IGP (interior gateway protocol routing algorithms)
- all routers in an autonomous subsystem engage with this
- Relies on IP addresses to construct paths

52
Q

What is an example of EGP?

A

BGP (border gate protocol)

53
Q

What is an example of IGP?

A

RIP (routing information protocol), OSPF (open shortest path first)

54
Q

Where do routers using RIP learn information from? And how often is it updated

A
  • In RIP each router learns the distance to each destination from its neighbours
  • Router sends update message to its neighbours every 30 seconds
55
Q

What is the metric to compute shortest path for RIP?

A

Number of hops

56
Q

2 Facts about RIP?

A
  • Runs on top of UDP
  • Uses mechanisms to reduce routing loops
57
Q

2 facts about OSPF?

A
  • Runs over IP (link-state)
  • OSPF enables each router to learn about the complete network topology.
58
Q

What does each router do in OSPF?

A
  • Monitors the cost of the link to each of its neighbours
  • Floods the link-state information to other routers on the network
59
Q

What is the inter-domain routing behind BGP based on?

A

Classless address prefixes as well as policy-based routing

60
Q

3 facts about BGP?

A
  • BGP establishes TCP connections
  • BGPv4 is a de-facto inter-domain routing protocol
  • Provides mechanisms for address aggregation
61
Q

What do the routers using BGP keep?

A

A global view of the internet in their RIBs (routing information bases)

62
Q

What does a BGP speaker do?

A

Exchange network reachability information with other BGP speakers (peers) adjacent to it –> (CONTAINING sequence of ASs that packets must traverse to reach a destination network)

63
Q

What are 2 famous internet management protocols?

A
  • ICMP (internet control message protocol)
  • SNMP (simple network management tool)
64
Q

What does network management include? (2)

A
  • Deployment (integration and coordination of HW and SW and human elements)
  • Monitor, test, poll, configure, analyse, evaluate and control the network and element resources to meet operational requirements
65
Q

Can network agents be hardware?

A

Yes, network agents can be hardware or software

66
Q

Describe the network management framework?

A
  • Managing server, (MS) with personnel
  • Managed device (MD) equipment (HW+SW)
  • MO: HW configuration parameters (e.g AS routing OSPF)
  • MIB (management information base)
  • Network management agent (inside the MIB)
  • Network management protocol
67
Q

Where is network management protocol needed?

A

Between the managed device and the managing serer

68
Q

What is SNMP briefly?

A
  • Application layer protocol to convey network-management control information messages between managing server and agent
  • It lies on top of UDP
69
Q

What is the most common use of SNMP?

A

Request-response mode: managing server send a request to an SNMP agent who performs some actions and sends a reply to request

70
Q

What is an example of an SNMP managing server request?

A

modify MIB (management information base) values.

71
Q

What is ICMP briefly?

A
  • Used by hosts and routers to communicate network-layer information to each other e.g error REPORTING
  • Lies on top of IP (it is not part of IP)
  • ICMP messages are carried in IP datagrams as payloads
72
Q

Example of the use of ICMP

A

When you get a message back form a HTTP session saying you can’t reach a destination network or something - that message is an ICMP message

73
Q

How does a host read an ICMP message delivered in an IP datagram?

A

It demulitplexes the datagram content to ICMP

Network Layer (6 decks)

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