202 Lecture Summaries

Lecture 2

• - Friendly Names
• - IP Addresses
• - Application Ports

Lecture 3

• - The InetAddress class deals with resolving names to addresses
• - The Socket class represents an individual connection established over the network
• - The ServerSocket class is a special type of socket used to allow new connections to be made
• - The PrintWriter class allows us to write individual lines of text over a socket
• - The BufferedReader class allows us to read lines of text from a socket

Lecture 4

• - Methods that block are a problem for communications systems as they prevent other clients getting service

Lecture 5

• • OSI 7 layer model
• • Encapsulation of information to form frames
• • Defined some physical characteristics of Ethernet
• • Wireless Ethernets, and issues of them

Lecture 6

• Ethernet
• • Frames
• • MAC addresses
• • Network Interface Cards
• • Hubs, switches
• • IP • Packets
• • IPv4 addresses
• • Routers

Lecture 7

• • ARP maps IPv4 addresses to Ethernet MAC addresses
• • NDP maps IPv6 addresses to Ethernet MAC addresses
• • ARP/NDP tables are dynamically managed
• • ARP/NDP tables are scoped to a single Ethernet bus
• • Standards documents (RFCs):
• • RFC 826: IPv4 ARP
• • RFC 4861: IPv6 Neighbor Discovery

Lecture 8

• • IP addresses contain a built-in network id
• • Useful scaling property: can often aggregate smaller network IDs into a single larger network ID.
• • Extract network ID by masking it out
• • Systems determine how to reach a destination by consulting their IP routing table

Lecture 9

• • IP Routing tables are organised so that the most specific route is chosen to a destination
• • Internet routing is organised using the BGP protocol
• • ASes
• • An AS being a network operated by a single organisation
• • In general, an AS prefers the highest preference route available, then the one with the shortest AS path length. Other rules follow, but these are two fundamental rules

Lecture 10

• • DNS is an application-level service that provides the ability to obtain an IP address from a more easily remembered name
• • DNS is implemented as a distributed hierarchical database
• • DNS has built-in redundancy, which the DNS application service takes advantage of
• • UDP is an unreliable transport protocol

Lecture 11

• • DNS is an application-level service that provides the ability to obtain an IP address from a more easily remembered name
• • DNS is implemented as a distributed hierarchical database
• • DNS has built-in redundancy, which the DNS application service takes advantage of
• • UDP is an unreliable transport protocol

Lecture 12

• •TCP is a transport protocol that is:
• • Reliable
• • Unacknowledged packets are retransmitted after they are lost and/or time out
• • connection-oriented,
• • Hosts establish connection with 3-packet handshake
• • tear-down connections with 4-packet exchange
• • stream-based • Client socket sees a stream of bytes, like reading or writing a file.
• • Does not see individual packets, or retransmitted packets, or connection establishment/teardown packets.

Lecture 13

• • TCP is the most widely used transport protocol in the Internet: reliable, byte-stream, connection oriented,
• • and FAIR!
• • TCP has to work on paths that vary with length (delay) and available capacity
• • TCP retransmit timer: decide when to declare a packet lost
• • Slow-start: quickly infer the rate at which TCP should be transmitting at
• • Congestion avoidance: slowly increase the rate at which new data is sent to avoid causing congestion
• • Fast retransmit / fast recovery: recover quickly from single packet loss

Lecture 14

• • Dynamic routing protocols are useful
• • Less tedious than manually reconfiguring all routers when links change (are added, removed, or otherwise change distance)
• • Less error prone
• • Better at responding to failures
• • OSPF is one example of an internal routing protocol
• • Link-state
• • Uses Dijkstra’s algorithm
• • Multicast: send data once to all interested receivers
• • OSPF uses multicast to send routing information to all routers it is connected to.

Lecture 15

• Encryption allows us to protect sensitive data traversing untrusted networks
• • One-way hashes and public key encryption allow us to build digital signatures
• • Authentication systems allow us to provide our identity across untrusted networks
• • Firewalls allow us to police traffic entering and exiting a network

Lecture 16

• • The TLS protocol provides a secure way to establish a symmetric key to encrypt communications
• • Protocol relies on certificate verification:
• • Is there a valid certificate path to a CA?
• • Does the hostname match that found in the certificate presented?

Lecture 17

• • Goal of today’s lecture was to discuss how to use the Java JSSE APIs to do TLS
• • Other APIs in other languages are similar. Use TLS libraries with care. Know what your responsibilities are.
• • JSSE will become more concrete in assignment five

Lecture 18

• • It became obvious fairly on in the early 1990s that the Internet was going to run out of addresses
• • CIDR, Private addresses bought us time
• • NAT is the price we paid
• • IPv6 is intended solution
• • Increasing deployment, has been defined for over 15 years (1998)
• • Service provider NAT not a good solution.
• • Deployment issues mostly at the edge of the network: enterprise and access networks.
• • Most large transit providers have deployed IPv6

Lecture 19

• • Today’s lecture was on elementary network debugging
• • Ping basic statistics on a path to a destination
• • Traceroute arrangement of routers on forward path
• • Both use ICMP
• • Try using ping and traceroute in the lab

Lecture 20

• UDP VS TCP