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Network and Security > Graeme > Flashcards

Graeme Flashcards

1
Q

What is Internetworking?

A
  • Hides routing from the Transport layer
  • The internet as a ‘network of networks
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2
Q

What are the function of the internet layer?

A
  • Internetworking
  • Transmitting packets
  • Receiving packets
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3
Q

What happens when the internet layer transmits packets?

A
  • Packetisation into datagrams
  • Processing and Routing IP datagrams
  • Fragmentation
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4
Q

What happens when the internet layer receives packets?

A
  • Error checking
  • Fragment Reassembly
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5
Q

What are the properties of the internet protocol?

A
  • Packet-switched: connectionless
  • Unreliable
  • Routed
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6
Q

What does unreliable in for the internet protocol?

A
  • No guarantee any given datagram will arrive
  • Packets sent and routed on a best effort basis
  • IP packets may get dropped or delayed (due to congestion/errors)
  • Quality of Service methods can help
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7
Q

What does routed mean for the internet protocol?

A
  • Usually destination-routed
  • Routers have routing tables and determine routing
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8
Q

What are the Internet Layer Protocols?

A

Internet Protocol:
- IPv4
- IPv6
Diagnostics, Control:
- ICMP
- ICMPv6
IPSEC - encryption/security
IGMP - helps establish IPv4 multicast groups

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9
Q

What are the characteristics of IPv4: RFC 791?

A
  • 32-bit addresses, written as dotted quads
  • Originated as part of ARPANET in the 1970s
  • Variable size header, minimum 20-bytes
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10
Q

What are the characteristics of IPv6: RFC 2460, 8200?

A
  • 128-bit addresses, written as ‘colon-hex’
  • Originated in the late 199-s
  • Fixed size, simpler header: 40 bytes
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11
Q

How can IPv6 addresses be simplifed?

A

We can omit leaders 0s in a block replacing them with a single set of “::”

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12
Q

How is fragmentation handled by IPv4?

A
  • Packets can be fragmented at any routing hop
  • Generally re-assembled at the receiving host, but could be done at any intermediate router
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13
Q

How is fragmentation handled by IPv6?

A
  • Packets may only be fragmented at the sending host
  • Must use Path MTU Discovery before sending
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14
Q

What is Classless Inter Domain Routing?

A

CIDR (introduced in 1993) allows variable length prefixes, reducing IPv4 address consumption

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15
Q

What do subnets do?

A

They limit the propagation of Ethernet broadcast traffic and segment hosts by logically dividing a larger IP allocation network

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16
Q

What do routers do in the internet protocol layer?

A
  • You need them any time there is a change in address space
  • It needs an interface for each network segment
  • Each interface needs an address that is reachable by hosts in that segment
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17
Q

What is Routing?

A

Routing describes how packets move between subnets
- Occurs at the internet layer and where there is a change in IP address space and each host has a routing table

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18
Q

What are Netmasks?

A
  • Specifies how many bits identify the network prefix
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19
Q

What is the Internet Control Message Protocol (ICMP)?

A

ICMP packets are encapsulated in standard IP packets

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20
Q

How is ICMP used for IPv4?

A

Used for information and error messages

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21
Q

How is ICMP is used for IPv6?

A

Also used for Router advertisement and neighbour discovery

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22
Q

What is Multicast?

A
  • One-to-many communication
  • Packets are only sent to hosts that are interested in them
  • Afterthought for IPv4, required for IPv6
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23
Q

What are uses for multicast?

A
  • One-to-many multimedia
  • Local service discovery
  • Inherently part of IPv6 for router advertisements, neighbour discovery and duplicate address detection
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24
Q

What is Address Resolution Protocol (ARP)?

A
  • Maps an IPv4 address on the local subnet to a MAC address
  • The host looking for a MAC address broadcasts an ARP “who has” request
  • The target sends a (unicast) reply to the requestor
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25
Q

What is Dynamic Host Configuration Protocol (DHCP)?

A

Automates the process for configuring addresses on a network for IPv4

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26
Q

How does Dynamic Host Configuration Protocol work?

A
  • When a host connects to a network, it broadcasts a DHCP DISCOVER message
  • The DHCP server reserves an address and replies with a DHCP OFFER
  • The client then needs to DHCP REQUEST the address
  • Finally, the server sends DHCP ACK, which contains lease duration and config
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27
Q

What is Neighbour Discovery Protocol?

A
  • Maps an IPv6 address on the local subnet to a MAC address
  • Uses ICMP and multicast, rather than encapsulated frames and broadcast
  • Router solicitations sent to a solicited node address
  • Router advertisements sent to the all nodes address
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28
Q

What does NDP replace?

A

ARP and ICMP router discovery

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29
Q

What are the 5 packet types for ICMPv6?

A
  • Router Solicitation
  • Router Advertisement
  • Neighbour Solicitation
  • Neighbour Advertisement
  • Redirect
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30
Q

What is Router Solicitation?

A

Host request for router information

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31
Q

What is Router Advertisement?

A

Router information. It carries the IPv6 network prefix (/64) to use and its source address implies the default router address

32
Q

What is Neighbour Solicitation?

A

Equivalent to ARP “who has”

33
Q

What is Neighbour Advertisement?

A

Equivalent to ARP reply

34
Q

What is Redirect?

A

Router informing host of a better first hop

35
Q

What is StateLess Address AutoConfiguration (SLAAC)?

A

SLAAC allows a host to autoconfigure basic network settings without a DHCPv6 server, specified by RA

36
Q

What does RFC7217 do?

A
  • Uses a pseudo-random function that takes the prefix, Network card identifier, Network identifier, DAD counter and secret key as arguments
37
Q

What is DHCPv6 (RFC8415)?

A

Similar to DHCP but
- Requires Router Advertisement
- Uses DHCP Unique Identifier instead of MAC address

38
Q

What are the benefits of IPv6?

A
  • Removes the need for NAT
  • More plug-and-play than IPv4
  • Streamlined header
  • Fragmentation only occurs at sender
39
Q

What are the barriers to IPv6 Deployment?

A
  • Time and Money
  • Hardware support
  • Regular users don’t want to learn something new
  • Chicken and egg situation with ISPs and content providers
  • “Peering wars” between Tier-1 network providers
40
Q

What is basic routing?

A
  • P1’s packet is sent to the nearest router
  • The packet is then passed on through the network
  • Eventually it arrives at P2
    (P1 and P2 are two different computers)
41
Q

What is IP Routing?

A
  • Occurs where there is a change in IP address space
  • A router has an IP address in each address space it routes between
  • There can be many routers between hosts on the internet
  • Parts of the IP header are re-written at each hop
42
Q

What is a routing table

A
  • Tells the host how to route traffic
  • All hosts on a network have one
  • May be built from information from DHCP or IPv6 RA
43
Q

What do routing tables include?

A
  • Destination prefixes and the interface or next hop to use
  • The local subnet that the host is connected to
  • a catchall default route
44
Q

How does a routing table work?

A
  • A set of rules
  • There can be multiple routes for one destination
  • The most specific matching route is picked first (Longest prefix)
  • The metric determines the priority of routes with the same specificity
45
Q

What are Autonomous Systems?

A

A large network or group of networks that has a unified routing policy. The internet is made of interconnected Autonomous Systems

46
Q

What are the three general categories of Autonomous Systems?

A
  • Multihomed
  • Transit
  • Single-homed/stub
47
Q

What is a routing protocol?

A

Allows router to build and exchange routing information automatically

48
Q

What protocols are used within an Autonomous System

A

Interior gateway protocols

49
Q

What protocols are used between Autonomous System

A

Exterior gateway protocols

50
Q

What are the two types of Interior Gateway protocols?

A
  • Distance Vector
  • Link state
51
Q

What is Distance Vector?

A
  • Talk only to directly neighbouring routers
  • Exchange “best” route information for any known prefixes with direct neighbours
52
Q

What is Link State?

A
  • Talk to all routers to establish full knowledge of the routers/topology in a site
  • Routers flood information messages describing their connected neighbours around entire site network
53
Q

What is Routing Information Protocol (RIP)?

A
  • Router sends its whole routing table periodically (every 30s) to directly connected routers
  • Destination network (prefix) and distance (cost) in hops
  • Receiving routers update their view of the best route to a given network
54
Q

What are the limitations of RIP?

A
  • Updates only every 30s
  • Updates are not acknowledged
  • Metrics are simple hop count values
  • Routers don’t have knowledge of network topology
  • Authentication is MD5, which is broken
55
Q

How does Link state routing work?

A
  • Messages are sent periodically, or any time a change in connectivity is detected
  • Both ends of a link must agree for it to be valid
    -All routers learn the full network topology
56
Q

How are Neighbours discovered?

A

With broadcast packets sent on all interfaces

57
Q

How is Link State better than Distance Vector?

A
  • Link State converges faster
  • Link state is better at avoiding loops
58
Q

What us Border Gateway Protocol? (BGP)

A
  • Works between Autonomous Systems
  • Distance-Vector-like, but includes information about the AS path associated with a given route, cost of paths and other rich attributes
58
Q

How does BGP work?

A
  • The IP of a neighbour is specified in config
  • Creates a BGP peering session (over TCP, port 179)
  • Then you advertise routes you know to your neighbours
59
Q

What are the downsides of BGP?

A
  • Relies on trust
  • Slow
  • Routers have limited BGP routing table size
60
Q

What is Traceroute?

A
  • Determines the route between two hosts
  • Sends packets with gradually increasing TTL
61
Q

What does the transport layer do?

A
  • Sends segments via the Network layer
  • Provides host-unique port numbers
  • Provides logical communication between applications
62
Q

How many bit port numbers do TCP and UDP use?

A

16 bit

63
Q

What are the features of TCP?

A
  • Connection oriented
  • Includes acknowledgements and retransmissions
  • Provides flow control/congestion control for segments it sends
  • TCP will adjust sending rate over time
  • Retransmission
  • Provides performance and reliability
64
Q

How does TCP establish connection?

A

There is a three way handshake: SYN, SYN-ACK and ACK. SYN opens connection
Each side uses a sequence number

65
Q

How is TCP reliable?

A
  • ACKS are sent back by receiver
  • Sender must detect lost packets
66
Q

What are the properties of UDP?

A
  • Connectionless
  • Retransmission/adaptation is up to the application (layer)
  • No flow control, often a fixed bit rate
  • Low overhead
67
Q

How big is the TCP header?

A

32 bits

68
Q

What is the difference between the UDP and TCP header?

A

The UDP header is much simpler where checksum is optional

69
Q

What is UDP loss?

A
  • Lossy/congested links can drop packets
  • Lower bandwidth links may drop packets as their buffers fill up
70
Q

What is the TCP/UDP service model?

A
  • Sender and receiver each create a socket to act as a communication endpoint
  • Socket has IP address and port number
  • Need five bits of information to identify communication
  • The sockets and protocol used, uniquely identify the applications subsequent data transmissions
71
Q

What is TCP Flow control?

A

Prevents a faster sender overwhelming a slow receiver

72
Q

How does TCP flow control work?

A
  • TCP uses a sliding window protocol to control sending rate
  • Sender should not send data unless receiver indicates it has buffer space to accept it
  • The sliding window is effectively the buffer space, the receiver says it has available at any given time
73
Q

What is TCP congestion control?

A

Reduces send rate to cope with network congestion

74
Q

How does TCP congest control work?

A
  • Maintained by the sender
  • The TCP congestion window indicates the number of bytes a sender may put into the network at any time
  • The congest window size starts slow, if successful, the this doubles the window every round trip
75
Q

What would be better for sending a video on YouTube?

A

TCP

76
Q

What is

A

Network and Security (2 decks)

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