Routing

Question 1

Lowest OSI layer that deals with end to end transmissions

Answer 1

Network Layer

Question 2

What determines the path the network takes

Answer 2

Routing Algorithms

Question 3

What do Routing Algorithms do

Answer 3

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

Question 4

Store and Forward

Answer 4

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

Question 5

Implementation of connectionless service

Answer 5

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

Question 6

Implementation of connection oriented service

Answer 6

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

Question 7

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

Answer 7

Avoids having to choose a new route for each packet

Question 8

Differences between VC and Datagram

Answer 8

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

Question 9

Routing vs Forwarding

Answer 9

Which routers to use vs What happens when packet arrives.

Question 10

Handles incoming packets

Answer 10

Routing

Question 11

Handles routing tables

Answer 11

Forwarding

Question 12

Routing Algorithm Features

Answer 12

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

Question 13

Routing Algorithms should handle changes of

Answer 13

topography and traffic

Question 14

Two classes of routing

Answer 14

Nonadaptive and Adaptive

Question 15

Non-Adaptive

Answer 15

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

Question 16

Adaptive

Answer 16

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

Question 17

Optimality Principle

Answer 17

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

Question 18

Sink trees

Answer 18

Used by algorithms, not necessarily unique.

Question 19

Shortest Path Algorithm

Answer 19

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

Question 20

Dijkstra Algorithm

Answer 20

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

Question 21

Permanent Path

Answer 21

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

Question 22

Flooding

Answer 22

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

Question 23

Problem with flooding

Answer 23

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

Question 24

Shortest Path first protocol uses

Answer 24

Flooding

Question 25

How to fix flooding

Answer 25

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

Question 26

If sender doesnt know path length

Answer 26

Initialize it to worst case

Question 27

A better flooding technique

Answer 27

Flood Damming

Question 28

Flood Damming

Answer 28

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

Question 29

Flooding uses

Answer 29

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

Question 30

Flooding Benefit

Answer 30

No other algorithm can produce shorter delay

Question 31

Load balancer

Answer 31

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

Question 32

Load balancer in UNIX

Answer 32

Generates 3 load average numbers

Question 33

System Load

Answer 33

Amount of computational work that a computer system performs.

Question 34

Load Average

Answer 34

Represents average system load over a period of time

Question 35

Idle computer load number

Answer 35

0. Each process using or waiting for CPU increases by 1

Question 36

Load average in single CPU systems

Answer 36

percentage of system utilization

Question 37

How to get percentage system utilization with multiple CPUs

Answer 37

Load average/No. of CPUS

Question 38

Why do busy sites employ 2 web servers

Answer 38

Can switch between them if one gets swamped

Question 39

Facebook load balancer computes

Answer 39

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

Question 40

Components of Load balancer

Answer 40

DNS load balancer and Software load balancer

Question 41

TinyDNS

Answer 41

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

Question 42

Authorative Nameserving

Answer 42

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

Question 43

Facebook decision engine

Answer 43

Cartographer

Question 44

Cartographer

Answer 44

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.

Question 45

DNS Load Balancer consists of

Answer 45

central GLB decision engine, and open source C DNS server

Question 46

Central GLB decision engine

Answer 46

making all traffic balancing decisions and generates DNS map.

Question 47

Open Source C DNS Server

Answer 47

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

Question 48

Authorative DNS Service

Answer 48

Allows others to find your domain

Question 49

Recursive DNS

Answer 49

allows you to resolve other people's domains

Question 50

When choosing a load balancer keep in mind:

Answer 50

Sticky or Stateless, and Software or Hardware

Question 51

Sticky

Answer 51

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

Question 52

Stateless

Answer 52

routes to most available server, based on internal algorithms

Question 53

Software Load Balancer

Answer 53

Like NLB, effective but not fine grained like hardware

Question 54

Hardware Load Balancer

Answer 54

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

Question 55

Web accelerators

Answer 55

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

Question 56

Factor for sites with growing traffic

Answer 56

availability of solution into hosting provider selection process.