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Noah Kantrowitz Open Source Bridge 2015 How The Internet Works The Life and Times of an HTTP Request

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It's not a big truck. It's a series of tubes. Ted Stevens

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We never, ever in the history of mankind have had access to so much information so quickly and so easily. Vint Cerf

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https:/ /www.google.com/

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https:/ /www.google.com/

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DNS

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DNS • Map names to IP addresses. • gethostbyname() • RFC 1034 & 1035. • "What is the A for www.google.com?"

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DNS Header ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID QR Opcode Opcode Opcode Opcode AA TC RD RA Z Z Z RCODE RCODE RCODE RCODE QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT

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DNS Header ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID QR Opcode Opcode Opcode Opcode AA TC RD RA Z Z Z RCODE RCODE RCODE RCODE QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT

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DNS Header ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID QR Opcode Opcode Opcode Opcode AA TC RD RA Z Z Z RCODE RCODE RCODE RCODE QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT

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DNS Header ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID QR Opcode Opcode Opcode Opcode AA TC RD RA Z Z Z RCODE RCODE RCODE RCODE QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT

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DNS Header ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID ID QR Opcode Opcode Opcode Opcode AA TC RD RA Z Z Z RCODE RCODE RCODE RCODE QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT QDCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT ANCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT NSCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT ARCOUNT

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DNS Question QNAME QTYPE QCLASS

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DNS Question QNAME QTYPE QCLASS

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DNS Question QNAME QTYPE QCLASS

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DNS Question QNAME QTYPE QCLASS

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DNS Message 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 0 1 1 1 0 1 1 0 1 1 0 0 0 1 1 0 0 1 0 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

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DNS Message 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 0 1 1 1 0 1 1 0 1 1 0 0 0 1 1 0 0 1 0 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

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DNS Message 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 0 0 0 0 1 1 0 0 1 1 0 0 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 1 1 0 1 1 0 0 1 1 1 0 1 1 0 1 1 0 0 0 1 1 0 0 1 0 1 0 0 0 0 0 0 1 1 0 1 1 0 0 0 1 1 0 1 1 0 1 1 1 1 0 1 1 0 1 1 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 1

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DNS Message 0001010000010000 0000000003777777 06676F6F676C6503 636F6D0000010001

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IP and UDP

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IP and UDP • Address and port. • 208.201.224.11:53 • Wrapped in order. • DNS inside UDP inside IP. • RFC 791 & 768.

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UDP Header Source Port Destination Port Length Checksum Data Data

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UDP Header Source Port Destination Port Length Checksum Data Data

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IP Header Version Version Version Version IHL IHL IHL IHL Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Flags Flags Flags Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Protocol Protocol Protocol Protocol Protocol Protocol Protocol Protocol Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Padding Padding Padding Padding Padding Padding Padding Padding

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IP Header Version Version Version Version IHL IHL IHL IHL Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Flags Flags Flags Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Protocol Protocol Protocol Protocol Protocol Protocol Protocol Protocol Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Padding Padding Padding Padding Padding Padding Padding Padding

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IP Header Version Version Version Version IHL IHL IHL IHL Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Flags Flags Flags Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Protocol Protocol Protocol Protocol Protocol Protocol Protocol Protocol Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Padding Padding Padding Padding Padding Padding Padding Padding

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IP Header Version Version Version Version IHL IHL IHL IHL Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Flags Flags Flags Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Protocol Protocol Protocol Protocol Protocol Protocol Protocol Protocol Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Padding Padding Padding Padding Padding Padding Padding Padding

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IP Header Version Version Version Version IHL IHL IHL IHL Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Type of Service Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Total Length Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Identification Flags Flags Flags Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Fragment Offset Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Time to Live Protocol Protocol Protocol Protocol Protocol Protocol Protocol Protocol Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Header Checksum Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Source Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Options Padding Padding Padding Padding Padding Padding Padding Padding

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IP Packet IP Header UDP Header DNS Packet

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Local Network

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Local Network • Computer • Switch • Router • Modem

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 default 192.168.1.1 eth0

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 default 192.168.1.1 eth0

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 default 192.168.1.1 eth0

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 default 192.168.1.1 eth0

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Ethernet • Wire framing. • MAC address. • Segments. • IEEE 802.3

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Segments • Electrical broadcast. • Thicknet. • 10BASE-T and hubs. • Switches.

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Ethernet Frame Preamble Preamble Preamble Preamble Preamble Preamble Preamble SFD Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Source Address Source Address Source Address Source Address Source Address Source Address Type Type Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding FCS FCS FCS FCS

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Ethernet Frame Preamble Preamble Preamble Preamble Preamble Preamble Preamble SFD Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Source Address Source Address Source Address Source Address Source Address Source Address Type Type Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding FCS FCS FCS FCS

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Ethernet Frame Preamble Preamble Preamble Preamble Preamble Preamble Preamble SFD Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Source Address Source Address Source Address Source Address Source Address Source Address Type Type Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding FCS FCS FCS FCS

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Ethernet Frame Preamble Preamble Preamble Preamble Preamble Preamble Preamble SFD Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Source Address Source Address Source Address Source Address Source Address Source Address Type Type Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding FCS FCS FCS FCS

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1000-BASET • Electrical signaling. • IEEE 802.3ab

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Ethernet Frame Preamble Preamble Preamble Preamble Preamble Preamble Preamble SFD Destination Address Destination Address Destination Address Destination Address Destination Address Destination Address Source Address Source Address Source Address Source Address Source Address Source Address Type Type Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding Data and padding FCS FCS FCS FCS

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ARP

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ARP • Bridge between IP and Ethernet. • NDP for IPv6. • "Who has IP address 1.2.3.4?" • In an Ethernet frame. • Broadcast FF:FF:FF:FF:FF:FF.

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ARP Packet HTYPE PTYPE HLEN PLEN OPER SHA SHA SHA SHA SPA SPA SPA THA THA THA THA TPA TPA TPA

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ARP Packet HTYPE PTYPE HLEN PLEN OPER SHA SHA SHA SHA SPA SPA SPA THA THA THA THA TPA TPA TPA

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ARP Packet HTYPE PTYPE HLEN PLEN OPER SHA SHA SHA SHA SPA SPA SPA THA THA THA THA TPA TPA TPA

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⌚

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Sending • Ethernet – 40:4A:3:ED:D2:1C • IP – 208.201.224.11 • UDP – 53 • DNS – www.google.com A

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Local Router

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Local Router • Static routing (again). • NAT.

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Route Table Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 173.228.34.0/24 * eth1 default 173.228.34.1 eth1

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 173.228.34.0/24 * eth1 default 173.228.34.1 eth1

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 173.228.34.0/24 * eth1 default 173.228.34.1 eth1

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 173.228.34.0/24 * eth1 default 173.228.34.1 eth1

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208.201.224.11 Destination Gateway Interface 127.0.0.0/8 * lo 192.168.1.0/24 * eth0 173.228.34.0/24 * eth1 default 173.228.34.1 eth1

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NAT • Rewrite IP and UDP header. • Source address and port. • Share one public address.

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Sending, Round Two • ARP lookup (or cached). • Ethernet frame. • Send to ISP border router.

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The Internet

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A Mesh of Trees • Tree-like at the edges. • Partial mesh in middle. • ~Full mesh in the core.

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Next Hops • Regional routers. • ISP backbone.

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BGP

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Routing Protocol • Distribute routes. • Update over time. • Find optimal paths.

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BGP • Gossip based. • Prefix based. • Share best routes. • RFC 4271.

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BGP • Gossip based. • Prefix based. • Share best routes. • RFC 4271.

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Autonomous Systems • 1-232 (née 216) • ~51000 so far. • AS7065

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IANA • ICANN department • Internet Assigned Numbers Authority • 5 Regional Internet Registries • AfriNIC, ARIN, APNIC • LACNIC, RIPE NCC

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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1 Weight 5 MED 2 Local Pref 6 Metric 3 AS Path 7 First 4 Origin 8 Tie Breaker BGP Algorithm

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Security • BGP Hijacking • Ingress Filtering • Rarely used signatures

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Backbone Router • AS46375 to AS7065

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DNS Server

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Receiving • Decode and match IP. • Decode UDP port. • Deliver to process.

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DNS Server • Decode question. • Check local cache. • Recursion?

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DNS Recursion

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Root Servers • 13 DNS servers. • Fixed IP addresses. • Maps TLDs to DNS servers. • [a-m].root-servers.net

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Recursion Round 1 • DNS query to 198.41.0.4 • com. IN NS a.gtld-servers.net • com. IN NS b.gtld-servers.net. • a.gtld-servers.net. IN A 192.5.6.30 • b.gtld-servers.net. IN A 192.33.14.30

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Recursion Round 2 • DNS query to 192.5.6.30 • google.com. IN NS ns1.google.com. • google.com. IN NS ns2.google.com. • ns1.google.com. IN A 216.239.32.10 • ns2.google.com. IN A 216.239.34.10

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Recursion Round 3 • DNS query to 216.239.32.10 • www.google.com. IN A 216.58.192.36

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DNS Reply • DNS message. • Headers & answer section. • Sent back over the wires. • Un-NAT.

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TCP

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TCP • Reliable ACKs. • Three-way handshake. • Congestion control. • RFC 675, 793, ...

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TCP Headers Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port Destination Port Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Data Offset Reserved U R G A C K P S H R S T S Y N F I N Window Window Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer Urgent Pointer Options Options Options Options Options Options Options Options Options Padding

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TCP Headers Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port Destination Port Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Data Offset Reserved U R G A C K P S H R S T S Y N F I N Window Window Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer Urgent Pointer Options Options Options Options Options Options Options Options Options Padding

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TCP Headers Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port Destination Port Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Data Offset Reserved U R G A C K P S H R S T S Y N F I N Window Window Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer Urgent Pointer Options Options Options Options Options Options Options Options Options Padding

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TCP Headers Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port Destination Port Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Data Offset Reserved U R G A C K P S H R S T S Y N F I N Window Window Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer Urgent Pointer Options Options Options Options Options Options Options Options Options Padding

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TCP Headers Source Port Source Port Source Port Source Port Source Port Source Port Source Port Source Port Destination Port Destination Port Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Sequence Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Acknowledgement Number Data Offset Reserved U R G A C K P S H R S T S Y N F I N Window Window Checksum Checksum Checksum Checksum Checksum Checksum Checksum Checksum Urgent Pointer Urgent Pointer Options Options Options Options Options Options Options Options Options Padding

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Three Way Handshake • SYN • SYN-ACK • ACK

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Acknowledgements • Send 1 ... 10. • ACK 10. • Send 11 ... 20. • ACK 15. • Send 15 ... 24.

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Extras • Slow-start • Avoidance • Fast resend • Karn's • Nagle's • SACK • Scaling • CUBIC

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TLS

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TLS (aka SSL) • Stream encryption. • Mutual authentication. • RFC 5246.

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Crypto

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TLS Handshake • ClientHello • ServerHello • ChangeCipherSpec • Finished

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Client Round 1 • ClientHello

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Server Round 1 • ServerHello • Certificate • ServerKeyExchange • ServerHelloDone

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Client Round 2 • ClientKeyExchange • ChangeCipherSpec • Finished

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Server Round 2 • ChangeCipherSpec • Finished

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Application Data • Data wrapper. • Transparent.

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HTTP

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HTTP • Request and response. • Verbs, paths, codes. • RFC 2616.

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HTTP Request • GET / HTTP/1.1 • Host: www.google.com

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Sending • TLS • TCP • IP • Ethernet

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HTTP Response • HTTP/1.1 200 OK • Content-Length: 17914 • \r\n •

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No content

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⌚

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How does the Internet work?

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Surprisingly well!

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Questions? @kantrn coderanger.net