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DE-CIX Academy Handout Networking Basics 04 - User Datagram Protocol (UDP) Wolfgang Tremmel [email protected] DE-CIX Management GmbH | Lindleystr. 12 | 60314 Frankfurt | Germany Phone + 49 69 1730 902 0 | [email protected] | www.de-cix.net Networking Basics DE-CIX Academy 01 - Networks, Packets, and Protocols 02 - Ethernet 02a - VLANs 03 - the Internet Protocol (IP) 03a - IP Addresses, Prefixes, and Routing 03b - Global IP routing 04 - User Datagram Protocol (UDP) 05 - TCP ... Layer Name Internet Model 5 Application IP / Internet Layer 4 Transport • Data units are called "Packets" 3 Internet 2 Link Provides source to destination transport • 1 Physical • For this we need addresses • Examples: • IPv4 • IPv6 Layer Name Internet Model 5 Application Transport Layer 4 Transport 3 Internet 2 Link 1 Physical Layer Name Internet Model 5 Application Transport Layer 4 Transport • May provide flow control, reliability, congestion 3 Internet avoidance 2 Link 1 Physical Layer Name Internet Model 5 Application Transport Layer 4 Transport • May provide flow control, reliability, congestion 3 Internet avoidance 2 Link • Examples: 1 Physical • TCP (flow control, reliability, congestion avoidance) • UDP (none of the above) Layer Name Internet Model 5 Application Transport Layer 4 Transport • May provide flow control, reliability, congestion 3 Internet avoidance 2 Link • Examples: 1 Physical • TCP (flow control, reliability, congestion avoidance) • UDP (none of the above) • Also may contain information about the next layer up Encapsulation Packets inside packets • Encapsulation is like Russian dolls Attribution: Fanghong. derivative work: Greyhood https://commons.wikimedia.org/wiki/File:Matryoshka_transparent.png Encapsulation Packets inside packets • Encapsulation is like Russian dolls • IP Packets have a payload Attribution: Fanghong. derivative work: Greyhood https://commons.wikimedia.org/wiki/File:Matryoshka_transparent.png Encapsulation Packets inside packets • Encapsulation is like Russian dolls • IP Packets have a payload • This payload is usually UDP or TCP (there are others as well) Attribution: Fanghong. derivative work: Greyhood https://commons.wikimedia.org/wiki/File:Matryoshka_transparent.png Encapsulation Packets inside packets • Encapsulation is like Russian dolls • IP Packets have a payload • This payload is usually UDP or TCP (there are others as well) • So we have an UDP packet inside an IP packet Attribution: Fanghong. derivative work: Greyhood https://commons.wikimedia.org/wiki/File:Matryoshka_transparent.png IPv4 Header "Legacy" IP Byte 0 1 2 3 • Starts with version and length Version | Header Length Total Length 0 DSCP / ECN • Total length of packet 20..65535 always 4 | 5..15 • Important: Time to live (TTL) 4 Identification Flags / Fragment Offset 8 Time To Live Protocol Header Checksum • Protocol: Type of payload 12 Source IPv4 Address Destination IPv4 Address TCP = 6, UDP = 17 16 • 20 24 Optional (if HeaderLength > 5) • Source / Destination address 32 bits 28 32 • Options (optional) IPv4 Header "Legacy" IP Byte 0 1 2 3 • Starts with version and length Version | Header Length Total Length 0 DSCP / ECN • Total length of packet 20..65535 always 4 | 5..15 • Important: Time to live (TTL) 4 Identification Flags / Fragment Offset 8 Time To Live Protocol Header Checksum • Protocol: Type of payload 12 Source IPv4 Address Destination IPv4 Address TCP = 6, UDP = 17 16 • 20 24 Optional (if HeaderLength > 5) • Source / Destination address 32 bits 28 32 • Options (optional) IPv6 Header Looks simpler, yes? Byte 0 1 2 3 • Starts with version and some labels 0 Version = 6 / Traffic Class / Flow Label Payload Length Next Payload length in bytes (0-65535) 4 Hop Limit • in bytes Header 8 • Next Header - you can chain more 12 Source IPv6 Address headers 16 20 • replaces protocol field, same 24 values 28 Destination IPv6 Address 32 • Hop Limit replaces TTL 36 • Addresses are now 128bits Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 0 Version = 6 / Traffic Class / Flow Label Payload Length Next 4 Hop Limit in bytes Header 8 12 Source IPv6 Address 16 20 24 28 Destination IPv6 Address 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Version = 6 / Traffic Class / Flow Label protocol Payload Length Next 4 Hop Limit in bytes Header 8 12 Source IPv6 Address 16 20 24 28 Destination IPv6 Address 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Version = 6 / Traffic Class / Flow Label protocol Payload Length Next 4 Hop Limit in bytes Header • UDP 8 12 Source IPv6 Address 16 20 24 28 Destination IPv6 Address 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Version = 6 / Traffic Class / Flow Label protocol Payload Length Next 4 Hop Limit in bytes Header • UDP 8 12 Source IPv6 Address • User Datagram Protocol 16 20 24 28 Destination IPv6 Address 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Version = 6 / Traffic Class / Flow Label protocol Payload Length Next 4 Hop Limit in bytes Header • UDP 8 12 Source IPv6 Address • User Datagram Protocol 16 20 • Protocol ID is 17 24 28 Destination IPv6 Address 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Version = 6 / Traffic Class / Flow Label protocol Payload Length Next 4 Hop Limit in bytes Header • UDP 8 12 Source IPv6 Address • User Datagram Protocol 16 20 • Protocol ID is 17 24 28 Destination IPv6 Address • Introduced in 1980 32 36 Next header: Transport layer header TCP, UDP, and more Byte 0 1 2 3 • We start with the "easiest" 0 Source Port Destination Port protocol • UDP 4 Length Checksum • User Datagram Protocol • Protocol ID is 17 • Introduced in 1980 • Lets have a look at the header UDP Header Byte 0 1 2 3 0 Source Port Destination Port 4 Length Checksum UDP Header • 4 fields, each of them 16 bits Byte 0 1 2 3 0 Source Port Destination Port 4 Length Checksum UDP Header • 4 fields, each of them 16 bits Byte 0 1 2 3 • Length: UDP header + UDP payload 0 Source Port Destination Port 4 Length Checksum UDP Header • 4 fields, each of them 16 bits Byte 0 1 2 3 • Length: UDP header + UDP payload 0 Source Port Destination Port • Checksum • Optional for IPv4, required for IPv6 4 Length Checksum • IP header + UDP header are covered UDP Header • 4 fields, each of them 16 bits Byte 0 1 2 3 • Length: UDP header + UDP payload 0 Source Port Destination Port • Checksum • Optional for IPv4, required for IPv6 4 Length Checksum • IP header + UDP header are covered • Source Port • Optional, zero if not used UDP Header • 4 fields, each of them 16 bits Byte 0 1 2 3 • Length: UDP header + UDP payload 0 Source Port Destination Port • Checksum • Optional for IPv4, required for IPv6 4 Length Checksum • IP header + UDP header are covered • Source Port • Optional, zero if not used • Destination Port number • required Port number Port number Port number UDP Destination port: 7 Port number UDP Destination port: 7 ? Port number 1 2 3 4 5 UDP 6 7 8 9 10 Destination port: 7 ? 11 12 13 14 Port number 1 2 3 4 5 UDP 6 7 8 9 10 Destination port: 7 11 12 13 14 Port number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Port numbers In reality... Port numbers In reality... • Of course we have not a building Port numbers root@linux:/tmp# netstat -an -u In reality... Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State udp 0 0 0.0.0.0:514 0.0.0.0:* udp 0 0 0.0.0.0:631 0.0.0.0:* udp 0 0 127.0.0.1:690 0.0.0.0:* • Of course we have not a building udp 0 0 0.0.0.0:45769 0.0.0.0:* udp 0 0 0.0.0.0:50191 0.0.0.0:* udp 0 0 0.0.0.0:5353 0.0.0.0:* udp 0 0 0.0.0.0:46721 0.0.0.0:* • We have a computer system udp 0 0 0.0.0.0:2049 0.0.0.0:* udp 0 0 127.0.0.1:39032 127.0.0.1:53 ESTABLISHED udp 0 0 0.0.0.0:43291 0.0.0.0:* udp 0 0 0.0.0.0:47544 0.0.0.0:* udp 0 0 127.0.0.1:52197 127.0.0.1:53 ESTABLISHED udp 0 0 0.0.0.0:36005 0.0.0.0:* udp 0 0 0.0.0.0:56663 0.0.0.0:* udp 0 0 0.0.0.0:60949 0.0.0.0:* udp 0 0 0.0.0.0:53 0.0.0.0:* udp 0 0 0.0.0.0:53 0.0.0.0:* udp 0 0 0.0.0.0:111 0.0.0.0:* udp 0 0 192.168.5.3:123 0.0.0.0:* udp 0 0 192.168.1.45:123 0.0.0.0:* Port numbers root@linux:/tmp# netstat -an -u In reality... Active Internet connections (servers and established) Proto Recv-Q Send-Q Local Address Foreign Address State udp 0 0 0.0.0.0:514 0.0.0.0:* udp 0 0 0.0.0.0:631 0.0.0.0:* udp 0 0 127.0.0.1:690 0.0.0.0:* • Of course we have not a building udp 0 0 0.0.0.0:45769 0.0.0.0:* udp 0 0 0.0.0.0:50191 0.0.0.0:* udp 0 0 0.0.0.0:5353 0.0.0.0:* udp 0 0 0.0.0.0:46721 0.0.0.0:* • We have a computer system udp 0 0 0.0.0.0:2049 0.0.0.0:* udp 0 0 127.0.0.1:39032 127.0.0.1:53 ESTABLISHED udp 0 0 0.0.0.0:43291 0.0.0.0:* • But we have port numbers udp 0 0 0.0.0.0:47544 0.0.0.0:* udp 0 0 127.0.0.1:52197 127.0.0.1:53 ESTABLISHED udp 0 0 0.0.0.0:36005 0.0.0.0:* udp 0 0 0.0.0.0:56663 0.0.0.0:* udp 0 0 0.0.0.0:60949 0.0.0.0:* udp 0 0 0.0.0.0:53 0.0.0.0:* udp 0 0 0.0.0.0:53 0.0.0.0:* udp 0 0 0.0.0.0:111 0.0.0.0:* udp 0 0 192.168.5.3:123 0.0.0.0:* udp 0 0 192.168.1.45:123 0.0.0.0:* Port numbers root@linux:/tmp# netstat -an -u In reality..
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