Ports/Headers

PortKeywordDescription
0—Reserved
1–4—Unassigned
5RJERemote job entry
7ECHOEcho
9DISCARDDiscard
11USERSActive users
13DAYTIMEDaytime
15NETSTATWho is up or NETSTAT
17QUOTEQuote of the day
19CHARGENCharacter generator
20FTP-DATAFile Transfer Protocol (data)
21FTPFile Transfer Protocol
23TELNETTerminal connection
25SMTPSimple Mail Transport Protocol
37TIMETime
39RLPResource Location Protocol
42NAMESERVERHostname server
43NICNAMEWho is
49LOGINLogin Host Protocol
53DOMAIN Domain name server
67BOOTPSBootstrap Protocol Server
68BOOTPCBootstrap Protocol Client
69TFTPTrivial File Transfer Protocol
75—Any private dial-out service
77—Any private RJE service
79FINGERFinger
95SUPDUPSUPDUP Protocol
101HOST NAMENetwork interface card (NIC) hostname server
102ISO-TSAPISO-Transport Service Access Point (TSAP)
103X400X400
104X400-SNDX400-SND
111SUNRPCSun Microsystems Remote Procedure Call
113AUTHAuthentication service
117UUCP-PATHUNIX-to-UNIX Copy Protocol (UUCP) Path Service
119NNTPUsenet Network News Transfer Protocol
123NTPNetwork Time Protocol
126SNMPSimple Network Management Protocol
137NETBIOS-NSNetBIOS name service
138NETBIOS-DGMNetBIOS datagram service
139NETBIOS-SSNNetBIOS session service
161SNMPSimple Network Management Protocol
162SNMP-TRAPSimple Network Management Protocol traps
512rexecUNIX remote execution (control)
513TCP—rlogin
UDP—rwho		TCP—UNIX remote login
UDP—UNIX broadcast name service
514TCP—rsh
UDP—syslog
TCP—UNIX remote shellUDP—system log
515Printer UNIX lineprinter remote spooling
520RIPRouting Information Protocol
525TimedTime server

IP Headers

ipheader
` version - Current IP Version / Used in IPv4 and IPv6 / Needed for IPv6 backwards-compatabile.
IHL - Length of the IP header in 32 bit increments
DSCP - Mechanism used for classifying network traffic on IP Networks https://www.sciencedirect.com/topics/computer-science/version-field
ECN - Explicit Congestion Notification - An extension to the Internet Protocol to the Transmision Control Protocol allows end-to-end notification of network congestion without dropping packets.
https://en.wikipedia.org/wiki/Explicit_Congestion_Notification Total Length - 16-bit field indicates to the entire size of ip packe header and data in bytes The minimum size 20 bytes (No Data) Maximum 65.535 bytes
Identification - The Ip packet is fragmented then each packet will use the same 16 bit number to identify which IP packet they belong to.
Flags 1rst bit is always set to 0 2nd bit is called the DG (Dont Fragment) 3rd bit is called the MF (More Fragments) bit and is set on all fragmented packets except the last one. Fragment Offset - 13th bit field specifies the position of fragment in the original fragmented IP packet. Time To Live - Every packet that passes through the router. the time to live field is decremented b 1. Once it hits 0 the router will drop the packet and sends an ICMP time exceeded messafe to the sender.The time to live filed has 8 bits and is used to prevent packets from looping around forever (if you have a routing loop)
Protocol Header Checksum - 16 bit field used to store a checksum of the header. The receiver can use the checksum to check if there are any errors in the header. Source Address - 32 bit source IP address Destination Address - 32 bit destination IP address Options - this field is not used often, is optional and has a variable length based on the options that were used. When you use this field, the value in the header length field will increase. An example of a possible option is “source route” where the sender
requests for a certain routing path.

Source - https://networklessons.com/cisco/ccna-routing-switching-icnd1-100-105/ipv4-packet-header

https://www.sciencedirect.com/topics/computer-science/version-field