XP0

Phase 1 · Reference

Cheat Sheet

Quick tables for OSI layers, ports, protocols, private ranges, and command examples.

osi

OSI layers

LayerPurposeExamples
7 ApplicationUser-facing protocolsHTTP, DNS, SMTP, SSH
6 PresentationEncoding, compression, encryptionTLS, JPEG, UTF-8
5 SessionConnection lifecycle and dialogsRPC, NetBIOS
4 TransportEnd-to-end deliveryTCP, UDP, QUIC
3 NetworkAddressing and routingIP, ICMP, OSPF
2 Data LinkFrames on the local linkEthernet, Wi-Fi, ARP
1 PhysicalSignals, media, bitsFiber, copper, radio
ports

Common ports

ProtocolPortTransportUse
HTTP80TCPPlain web traffic
HTTPS443TCP/UDPEncrypted web, HTTP/3 over UDP
DNS53UDP/TCPName resolution
SSH22TCPRemote shell
SMTP25TCPMail transfer
IMAP143/993TCPMailbox access
DHCP67/68UDPAutomatic IP assignment
NTP123UDPTime sync
ranges

Private ranges

RangeSizeNote
10.0.0.0/816,777,216Large internal networks
172.16.0.0/121,048,576Enterprise/private blocks
192.168.0.0/1665,536Home and small office LANs
127.0.0.0/816,777,216Loopback to this host
169.254.0.0/1665,536Link-local fallback
dns

DNS records

TypeUseExamples
AName to IPv4 addresspacket.school -> 203.0.113.24
AAAAName to IPv6 addresspacket.school -> 2001:db8::24
CNAMEAlias to another namewww -> packet.school
MXMail exchanger10 mail.packet.school
TXTText policies and verificationv=spf1 include:...
NSAuthoritative name serverns1.packet.school
commands

Command quickstart

CommandTells you
ping packet.schoolReachability and round-trip time
traceroute packet.schoolHop-by-hop path to a target
nslookup packet.schoolDNS answer from a resolver
dig A packet.schoolDetailed DNS response
ipconfig /allWindows interface configuration
ip addrLinux interface addresses
netstat -rnRouting table