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Networks > Application Layer > Flashcards

Application Layer Flashcards

1
Q

What is DNS?

A

Domain Name System - maps urls/names to addresses. (IPv4, IPv6, MAC)

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2
Q

WHat is DHCP?

A

Dynamic Host Protocol - Allocates dynamic IPv4 addresses.

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3
Q

What is the process of DHCP? (4)

A

DHCP Discover - Client requests IP address
DHCP Offer - DHCP offers IP address/es to client.
DHCP Request - Client selects IP address and requests it.
DHCP Ack - DHCP confirms selection.

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4
Q

What is telent?

A

Unencrypted terminal emulation protocol. Not used over Internet anymore, mostly used to communicate with old machines.

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5
Q

What has telnet been replaced by?

A

SCP and SSH

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6
Q

What is SMTP?

A

Simple Mail Transfer Protocol, used to reliably send emails, usually over TCP connection.
Can be extended with authentication.

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7
Q

What is IMAP?

A

Internet Message Access Protocol - usedto send emails over TCP connection. Ports 134/993 (secure)

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8
Q

What is HTTP?

A

Text-based protocol for transfering hypermedia contexts.

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9
Q

What are the 5 requests of HTTP?

A

GET, POST, PUT, DELETE, HEAD

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10
Q

What is QUIC?

A

Quick UDP Internet Connection - Uses UDP to transfer packets quickly on the web. Used by chrome - experimental.

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11
Q

What is CoAP?

A

Constrained Application Protocol - Uses MQTT-based publish/subscribe method to share messages. Used for devices with less resources like IoT devices.

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12
Q

What is RTSP and what packet transfer method does it use?

A

Real-Time Streaming Protocol, using UDP for fast transfer of packets.

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13
Q

What are the 4 main file transfer protocols?

A

SMB - Server Message Block - Microsoft, provides authentication and file locking.
NFS - Network File Service - Linux
P2P - Peer-to-peer - uses trackers (BitTorrent)
FTP - File Transfer Protocol

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14
Q

What is MQTT?

A

Publish-subscribe network protocol.
Messages published to a broker.
Clients subscribe to data streams.
Messages are tagged so only clients that are subscribed to that tag receive the message.

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15
Q

What is CoAP?

A

Lightweight, RESTful, modern version of MQTT, used for devices with less resources.

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16
Q

What is in a CoAP request?

A

Message id, RESTful request (e.g. GET)

17
Q

What is in a CoAP response?

A

Message ID, Ack and Payload. (Unless payload is too big, then Ack and payload are sent separately.

18
Q

Why/when are CoAP proxies used?

A

When the servers are ‘sleepy’ nodes (not always listening for requests).
The proxies store the requests and when the server becomes active, it sends the cached requests.

19
Q

What are block transfers in CoAP?

A

Large payloads are broken down into chunks and sent to the client.
The client rebuilds the payload.

20
Q

What is the function of DNS?

A

To convert user-friendly URLs to address (IPv4, IPv6, MAC)

21
Q

What are the record types for IPv4 and IPv6?

A

IPv4 - A record

IPv6 - AAAA record.

22
Q

What is a DNS resolver?

A

A local DNS server that receives and ‘resolves’ requests.

23
Q

Where does a client get the IP address for a DNS from?

A

DHCP.

24
Q

What is the DNS hierarchy?

A

Root servers -> Top Level Domains -> Sub-domains NS -> Resolvers

25
Q

What is the recursive DNS lookup?

A

If the resolver doesn’t have the required DNS record, it requests it from a root server.
The root server responds with the address of a DNS that could have the response.
This repeats until the correct record is found. (The resolver ‘walks’ the hierarchy)

26
Q

Which port is used for DNS communication?

A

Port 53

27
Q

Which port is used for DHCP?

A

Port 67

28
Q

Which port is used for HTTP?

A

Port 80

29
Q

Why is UDP good for DNS? (2)

A

Efficient

Connectionless - good for handling DNS abuse

30
Q

Why does a DNS need to be resilient?

A

It is critical infrastructure for the internet, so therefore vulnerable to DDoS attacks.

31
Q

Why are there multiple (350+) DNS root servers? (2)

A

To share load balancing - client is directed to nearest alive server.
For greater resilience - If one server goes down/is attacked, clients can be directed to the next nearest alive server.

32
Q

What are the security solutions for DNS? (3)

A

Block spoof IPs.
Block resolver lookups from non-local IPs.
DNSSEC - adds signatures to requests.

33
Q

What is an issue with DNSSEC?

A

It makes the responses a lot larger which can make managing them complex.

Networks (4 decks)

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