Week 3 - Net Flashcards
What is global connectivity
connectivity between network clouds
What layer is the IP router commonly situated on?
Network layer
What is IP service referred to as?
Best Effort
What does best effort mean?
whatever you get at the time of transmission
Is IP connection-less or connection orientated?
connection less
Some factors of the IP being connection-less?
- no connection set up
- send and forget
- unconfirmed
- unreliable
- data source is not constrained on transmisson
- no direct access, only access via transport protocol
How is an IP address found?
A FQDN is looked up in the global directory service (DNS) and a corresponding IP address is found.
What does an IP address identify as?
an interface on a host (ex, ethernet or wireless LAN) and not the host itself
Give some uses of IP addresses?
identification – allows hosts to be unqiuely labelled
transport protocols - forms part of the identity of a transport packet flow
bound to an interface on an IP host - multiple interfaces, multiple IP addresses
used for routing and forwarding - discover network paths, transmit packets towards their destination.
What does DNS stand for
domain name system
what is the DNS
global distributed directory service, it maps domain names to IP addresses
What are the DNS’ distributed services
- nameservers
- resolvers
Describe DNS global system
- must be scalable
- distributed data and admin responsibility
- localised caching
What is a DNS namespace?
- global distributed namespace
- nodes through a tree
- domain, single network or multiple
- DNS servers, servers for each domain
What are the 3 DNS applications?
- nameservers
- resolvers
- protocol
What are client applications in resolvers?
- host
- dig
- nslookup
How does DNS name resolution work?
query to local server
- local server checks cache
- may query root server
- root server may redirect query
Where does the authoritative answer in DNS name resolution come from?
domain server
Where does the non-authoritative answer in DNS name resolution come from?
-from cache at local server
What is the local server in name resolution? Describe.
- recursive
- queries other servers to resolve request
- result stored in cache
- resukt used to answer other queries
- TTL controls caching
What is the local server within an organisation? Regarding DNS?
- recursive for local use
- iterative for others
What is the root server in name resolution? Describe.
- iterative
- sends a referral to the requester
- referral gets closer to the actual server that holds the mapping
- not recursive due to load and security
What is the root server within an organisation? Regarding DNS?
-for external users
What is held in the TCP header?
source and destination port numbers
what is held in the TCP payload?
data from the layer above
Describe the TCP service?
- connection orientated
- ordered
- confirmed
- reliable
- byte-stream service
What is the TCP protocol data structure?
segment header fornat
What is the TCP algorithm protocol?
-FSM for protocol state
-plus various algorithms for
reliability, flow control, congestion control
What does ACK stand for?
acknowledgement significant
What does SYN stand for?
synchronise sequence numbers
what does FIN stand for
no more data from sender
Describe TCP connection set-up
- active open - 3 way handshake
- passive open
- local connection name
- use SYN and SYN ACK
describe TCP connection tear down?
- clean termination
- abortive termination uses RST flag
Once TCP connection established, what does it follow?
-flow control and congestion control algorithms
What is the 5 tuple for TCP endpoints?
What are server port numbers?
- well known
- 80 for HTTP
- 443 for HTTPS
What are client port numbers?
- typically ephemeral
- allocated by OS
- connection to same server will have different client port numbers
What are causes on congestion?
- too many packets
- buffer overflow in routers
- unpredictable traffic patterns
- time-of-day traffic
What are the effects of congestion?
- higher end to end delay
- lost packets
- network instability
- loss of service
How does TCP congestion control work?
- start slow
- send 1 segment, f successfully ACK’d send 2, then 4 then 8
- until a missing for delayed ACK then drop to hald and increase linearly
What are TCP transmissions not protected from?
inspection
forgery
modification
replay
What are not security mechanisms?
reliability
flow control
congestion control
When would you use UDP?
where reliability does not matter and delay does
Why use UDP?
no end-to-end delay
control of data transmission rate
Service description of UDP?
connectionless unconfirmed unrelaible datagram service - a thin layer on top of IP, uses best effort service
UDP data structure protocol?
packet format
UDP algorithm protocol?
simple send/recieve of independent packets
What is the UDP endpoint 5 tuple?
Main differences between TCP and UDP?
TCP - send and wait, reliable delivery, CO
UDP - send and hope, no flow control, no congestion control, CL
What type of communication can UDP permit?
unicast
multicast
What is multicast?
many|one to many
- the destination IP address is a multicast group address
- anyone can send to group
- must be a member of group to receive
What is QUIC?
Quick UDP Internet Connections
- based on UDP but with security, multiplexing etc
What is multicast popular for?
LAN discovery protocols
- devices and services advertise their presence
