Basics of Networking
A network is a collection of interconnected devices that communicate and share resources using a set of defined protocols over a common transmission medium.
Networking is the process of connecting various devices so that they can communicate with each other and share information and resources
Network protocols are sets of rules or standards used by devices to communicate with each other over a network.
Network protocols can be broadly categorized into "layers". Each layer relies on the layer below it and provides services to the layer above it. This table covers the most essential protocols across networking layers and use cases ->
Protocol
Use
Port(s)
Standard
HTTP
Web browsing
80
RFC 2616, RFC 7230–7235
HTTPS
Secure web browsing
443
RFC 2818, RFC 5246 (TLS)
FTP
File transfer
20 (Data), 21 (Control)
RFC 959
SMTP
Sending email
25
RFC 5321
IMAP
Retrieving email
143
RFC 3501
POP3
Retrieving email
110
RFC 1939
DNS
Domain name resolution
53
RFC 1034, RFC 1035
DHCP
Dynamic IP address allocation
67 (Server), 68 (Client)
RFC 2131
Telnet
Remote command-line interface
23
RFC 854
SSH
Secure remote access
22
RFC 4251–4254
TCP
Reliable data transport
None (Layer 4 protocol)
RFC 793
UDP
Unreliable, fast data transport
None (Layer 4 protocol)
RFC 768
ICMP
Network diagnostics
None (Layer 3 protocol)
RFC 792
SNMP
Network management
161 (Agent), 162 (Trap)
RFC 1157
LDAP
Directory services
389
RFC 4511
NTP
Time synchronization
123
RFC 5905
TFTP
Simple file transfer
69
RFC 1350
SFTP
Secure file transfer
22 (over SSH)
RFC 4253
RDP
Remote desktop protocol
3389
Proprietary (Microsoft)
SIP
Voice over IP signaling
5060, 5061
RFC 3261
SMB
File and resource sharing on Windows
445
CIFS, SMB Protocol
MPLS
Packet forwarding based on labels
None
RFC 3031
BGP
Routing information exchange
179
RFC 4271
OSPF
Internal routing protocol
None
RFC 2328
RIP
Distance vector routing protocol
520
RFC 2453
LLDP
Link Layer Discovery Protocol
None
IEEE 802.1AB
ISAKMP
Key management for IPsec
500
RFC 2408
ESP
Encapsulating Security Payload (IPsec)
None (Layer 3 protocol)
RFC 4303
GRE
Tunneling protocol
None
RFC 1701, RFC 1702
PPTP
VPN protocol
1723
RFC 2637
L2TP
VPN tunneling protocol
1701, 1702
RFC 2661
SCTP
Reliable, message-oriented transport
None
RFC 4960
XMPP
Messaging and presence
5222, 5269
RFC 6120, RFC 6121
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