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Networking > Routing > Flashcards

Routing Flashcards

1
Q

Lowest OSI layer that deals with end to end transmissions

A

Network Layer

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2
Q

What determines the path the network takes

A

Routing Algorithms

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3
Q

What do Routing Algorithms do

A

Decide what path the network takes AND decides which output line an incoming packet should be transmitted on

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4
Q

Store and Forward

A

Packets sent to nearest router and that router verifies it and sends it onto the next router until it arrives at destination

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5
Q

Implementation of connectionless service

A

Packets injected into datagram network individually and routed independently. Packets called datagrams.

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6
Q

Implementation of connection oriented service

A

AKA Label-Switching. Path from source to destination setup for packets to be sent.

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7
Q

What does a connection oriented service avoid (In comparison to connectionless)

A

Avoids having to choose a new route for each packet

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8
Q

Differences between VC and Datagram

A

VC needs setup phase, Datagram wastes space with address. VCs guarantee QoS but are vulnerable to crashes.

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9
Q

Routing vs Forwarding

A

Which routers to use vs What happens when packet arrives.

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10
Q

Handles incoming packets

A

Routing

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11
Q

Handles routing tables

A

Forwarding

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12
Q

Routing Algorithm Features

A

Correctness, Simplicity, Robustness, Stability, Fairness, Efficiency.

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13
Q

Routing Algorithms should handle changes of

A

topography and traffic

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14
Q

Two classes of routing

A

Nonadaptive and Adaptive

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15
Q

Non-Adaptive

A

Do not base their decisions over estimates of network topology. Don’t respond to failures. Route computed in advance

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16
Q

Adaptive

A

Vary routing decisions according to changes in topology and traffic. Dynamic routing algorithms differ in where they obtain info from.

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17
Q

Optimality Principle

A

If Router A is on the optimal path from router B to router C then the optimal path from A to C falls on the same route

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18
Q

Sink trees

A

Used by algorithms, not necessarily unique.

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19
Q

Shortest Path Algorithm

A

Build a graph of the network with each node being a router and each edge being a communication line. Measure length by hops.

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20
Q

Dijkstra Algorithm

A

Finds shortest path between source and all destinations. Labeled by distance. Uses temporary and permanent paths

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21
Q

Permanent Path

A

A path is made permanent when they are 100% known to be the shortest route.

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22
Q

Flooding

A

Every incoming packet is sent out on every outgoing line besides the one it arrived on.

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23
Q

Problem with flooding

A

generates a lot of duplicate patterns and will become infinite without countermeasures

24
Q

Shortest Path first protocol uses

A

Flooding

25
Q

How to fix flooding

A

Add a hop count in packet header, decrement it at every hop and discard when = 0

26
Q

If sender doesnt know path length

A

Initialize it to worst case

27
Q

A better flooding technique

A

Flood Damming

28
Q

Flood Damming

A

Having routes keep track of which packets have already been flooded. Can do this by putting a sequence of numbers on packet.

29
Q

Flooding uses

A

ensures packets are delivered to every node, all messages transmitted can be received by other stations in range

30
Q

Flooding Benefit

A

No other algorithm can produce shorter delay

31
Q

Load balancer

A

Distributes incoming HTTP requests amongst servers in server farm to avoid overloading any one server

32
Q

Load balancer in UNIX

A

Generates 3 load average numbers

33
Q

System Load

A

Amount of computational work that a computer system performs.

34
Q

Load Average

A

Represents average system load over a period of time

35
Q

Idle computer load number

A
  1. Each process using or waiting for CPU increases by 1
36
Q

Load average in single CPU systems

A

percentage of system utilization

37
Q

How to get percentage system utilization with multiple CPUs

A

Load average/No. of CPUS

38
Q

Why do busy sites employ 2 web servers

A

Can switch between them if one gets swamped

39
Q

Facebook load balancer computes

A

load and determines which cluster to point each ISP’s user to. Handles traffic balancing and network optimization.

40
Q

Components of Load balancer

A

DNS load balancer and Software load balancer

41
Q

TinyDNS

A

by Bernstein Handles. Contains authorative nameserving. Only Clients are recursive nameserving - interpolates with relevant DNS standards.

42
Q

Authorative Nameserving

A

via UDP, no recursive nameserving and does not respond to TCP

43
Q

Facebook decision engine

A

Cartographer

44
Q

Cartographer

A

Gathers info on topology, latency, bandwidth etc to determine best cluster point for each ISP. Pushes new DNS maps to server when cluster load is to be adapted to. Reacts to internal FB network problems and can deal with localized outages.

45
Q

DNS Load Balancer consists of

A

central GLB decision engine, and open source C DNS server

46
Q

Central GLB decision engine

A

making all traffic balancing decisions and generates DNS map.

47
Q

Open Source C DNS Server

A

DNS traffic, directs users to clusters based on lookup table on DNS map.

48
Q

Authorative DNS Service

A

Allows others to find your domain

49
Q

Recursive DNS

A

allows you to resolve other people’s domains

50
Q

When choosing a load balancer keep in mind:

A

Sticky or Stateless, and Software or Hardware

51
Q

Sticky

A

routes user back to same server during the life of a session

52
Q

Stateless

A

routes to most available server, based on internal algorithms

53
Q

Software Load Balancer

A

Like NLB, effective but not fine grained like hardware

54
Q

Hardware Load Balancer

A

Offloads all processing off web servers but can be complex to configure and administer

55
Q

Web accelerators

A

Can cache pages, static assets and do RR load balancing for backend

56
Q

Factor for sites with growing traffic

A

availability of solution into hosting provider selection process.

Networking (7 decks)

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