User Datagram Protocol - UDP Header (RFC 768)
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Byte Offset 0
Byte Offset 1
Byte Offset 2
Byte Offset 3
Source Port Number (16-bit)
Destination Port Number (16-bit)
Byte Offset 4
Byte Offset 5
Byte Offset 6
Byte Offset 7
Length (16-bit)
Checksum (16-bit)
Byte Offset 8
Byte Offset 9
Byte Offset 10
Byte Offset 11
data (variable length…)
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Common Port Numbers
D
Hex
Protocol
D
Hex
Protocol
D
Hex
Protocol
7
0x07
echo
69
0x45
tftp
500
0x1F4
isakmp
19
0x13
chargen
123
0x7B
ntp
514
0x202
syslog
37
0x25
time
137
0x89
netbios-ns
520
0x208
rip
53
0x35
domain
138
0x8A
netbios-dgm
33434
829A
traceroute
67
0x43
bootps
161
0xA1
snmp
68
0x44
bootpc
162
0xA2
snmp-trap
Length
Number of bytes in the entire datagram including header
minimum value 8 bytes
(Which is the length of just the header with no data)
maximum value 65515 bytes (or 65507 bytes of UDP data)
(Max IP is 65535 bytes - 20 byte header = 65515 bytes for UDP packet - 8 bytes of UDP header = 65507)
Checksum
Covers psedo header (IP Header source and destinstation addresses, the protocol and UDP length) and entire UDP
datagram
(Note: By RFC, the crc is not required)
