April 6th notes

Internet weaknesses

Networking Infrastructure

Host - [ISP] - [ISP] - Host

-Anyone can be an ISP

-local and interdomain routing

• TCP/IP for routing/messaging
• BGP for touting announcements

Domain Name System

-Find IP address from symbolic name

Layers of the internet

• Built on a hierachichal set of protocols
• Think as a correspondence between specific layers

TCP Protocol Stack

Application - Application TCP - Transport Port # IP - Network IP addr Link - Network Link MAC address

What does data look like at each layer? App: app data

broken into

TCP: TCP	segment
IP: IP	packets
Link: frame ETH	IP	TCP	data	ET

What does a TCP header contain? 32 bits * 7 Source port | dest port seq num ack num data offset window checksum | urgent pointer options | padding Data

IP Addressing

32 bits total 4 8 bit segments (uint rep) prefix: set of addresses w/ same initial x bits

How does routing work?

Say Meg wants to send a msg to Tom. She sends a packet with src and dst ip to her router. Each router has a forwarding table For each destination prefix, it has a next hop ip; the next router to send a packet to on its path

Packets can take different paths, and arrive out of order no ordering/delivery route guarantee.

NATS = Private address space

How can we still be adding computers to the network?

• Have ‘local’ addresses that router NATS to global IP space

User Datagram Protocol

unreliable

• No acks/ congestion control
• Used for VoIP, video, NTP
• lactency matters more than reliability

UDP header [src port	dst port] (32 bits)
[length	cksum ]

Problem: No src IP auth Burden on client to embed correct source IP

TCP

Connection oriented, preservers order If you know the sequence number, you can insert packets into the connection. The random seq nonce used in the initial Handshake helps protect against this.

Vulnerable to flood attacks.