Application Layer Flashcards
What is DNS?
Domain Name System - maps urls/names to addresses. (IPv4, IPv6, MAC)
WHat is DHCP?
Dynamic Host Protocol - Allocates dynamic IPv4 addresses.
What is the process of DHCP? (4)
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.
What is telent?
Unencrypted terminal emulation protocol. Not used over Internet anymore, mostly used to communicate with old machines.
What has telnet been replaced by?
SCP and SSH
What is SMTP?
Simple Mail Transfer Protocol, used to reliably send emails, usually over TCP connection.
Can be extended with authentication.
What is IMAP?
Internet Message Access Protocol - usedto send emails over TCP connection. Ports 134/993 (secure)
What is HTTP?
Text-based protocol for transfering hypermedia contexts.
What are the 5 requests of HTTP?
GET, POST, PUT, DELETE, HEAD
What is QUIC?
Quick UDP Internet Connection - Uses UDP to transfer packets quickly on the web. Used by chrome - experimental.
What is CoAP?
Constrained Application Protocol - Uses MQTT-based publish/subscribe method to share messages. Used for devices with less resources like IoT devices.
What is RTSP and what packet transfer method does it use?
Real-Time Streaming Protocol, using UDP for fast transfer of packets.
What are the 4 main file transfer protocols?
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
What is MQTT?
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.
What is CoAP?
Lightweight, RESTful, modern version of MQTT, used for devices with less resources.
What is in a CoAP request?
Message id, RESTful request (e.g. GET)
What is in a CoAP response?
Message ID, Ack and Payload. (Unless payload is too big, then Ack and payload are sent separately.
Why/when are CoAP proxies used?
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.
What are block transfers in CoAP?
Large payloads are broken down into chunks and sent to the client.
The client rebuilds the payload.
What is the function of DNS?
To convert user-friendly URLs to address (IPv4, IPv6, MAC)
What are the record types for IPv4 and IPv6?
IPv4 - A record
IPv6 - AAAA record.
What is a DNS resolver?
A local DNS server that receives and ‘resolves’ requests.
Where does a client get the IP address for a DNS from?
DHCP.
What is the DNS hierarchy?
Root servers -> Top Level Domains -> Sub-domains NS -> Resolvers
