Internet basics

• The Internet
• Interdomain routing; BGP; valley-free
• Path properties
• TCP and UDP
• Socket basics; echo server

The Internet

• Rounters
• Switches
• Packet switching

IP addresses

How do routers know where to send a packet？

• Internet protocal
• Each machine is assigned with an IP address
• Each packet has a source and destination address
• Each router has a forwading table that maps ranges to links over which packet in that ranges should be sent ("next hop")

ICMP

• ping

• Trace route

• IP address ranges are assigned by the IANA (Internet Assigned Numbers Authority)

  • IANA delegates this taks to five regional internet registries (RIRs)

• You can use tools like whois to see who a given IP belongs to

IPv4 vs IPv6

• IPv4: early 80s, 32-bit addresses
• IPv6: early 90s, 128-bit addresses
  • Technical improvements
  • run out of IPv4 addresses at this point
• IPv6 is widely deployed now, but not yet ubiquitous

Routing

Interdomain routing

• Networks continuously exchange routes to IP prefixes

BGP (Border Gateway Protocol)

• The internet is divided into autonomous systems (ASes)

AS-level connectivity

Customer, providers, and peering

• certain business relationships with each other
• customer/provider
• customer will announce itself, its customer, not announce Peering to provider
• provider will announce itself, its customer and Peering to provider

Q1: Consider Network 2 and its provider, Network 3. Which path(s) does Network 3 announce to Network 2?

A,B,C

Q2: Consider Network 3 and its customer, Network 2. Which path(s) does Network 3 announce to Network 2?

D,E,F

Q3: Network E 5 to Network 3

e

Q4: Consider Network 1 and its provider, Network 2. Which path(s) does Network 2 announce to Network 1?

CDEF

Tiers

Valley-free routing

Path properties

Queueing delay, loss

What if we send packets too quickly

TCP & UDP

Transmission Control Protocol

Congestion Control

Decide how fast should the sender send

Problem: Availability capacity not known

Congestion control

• congestion window of max packets in flight
• Slow start: exponential increase until threshold or a drop is detected
• increase cwnd by one packet for each incoming ACK
• Congestion avoidance: additive increase, multiplicate decrease (AIMD)

Port numbers

UDP

User datagram protocol

not all application need TCP Reliable stream abstraction

• Internet paths are not perfect
• TCP provides

Socket

operations

• socket: create
• bind
• listen
• send/sendto/write
• Recv/recvfrom/read
• close

Java example: sender

• create a socket
• write data

Receiver

• bind to a port

W

netstat tool to show which sockets exist locally