NETOps / Study

Certification Memory.

Dense recall material for the concepts that keep appearing across IT and networking exams. Search it when working; flip the cards when studying. Vendor commands and exam objectives vary, so use this as a memory layer—not a replacement for the current objectives of a specific certification.

Quick Quiz

COMMON PORTS

Numbers worth instant recall.

20/21 TCPFTP data / control
22 TCPSSH, SFTP/SCP over SSH
23 TCPTelnet
25 TCPSMTP
53 TCP/UDPDNS
67/68 UDPDHCP server / client (IPv4)
80 TCPHTTP
110 TCPPOP3
123 UDPNTP
143 TCPIMAP
161/162 UDPSNMP queries / traps
389 TCP/UDPLDAP
443 TCPHTTPS
445 TCPSMB
636 TCPLDAPS
3389 TCP/UDPRDP
OSI / TCP-IP

Know where the problem lives.

L7Application — HTTP, DNS, SMTP
L6Presentation — encoding, encryption concepts
L5Session — session establishment/management concepts
L4Transport — TCP/UDP, ports
L3Network — IP, routing
L2Data Link — Ethernet, MAC, switching, VLANs
L1Physical — cable, radio, signal
Mnemonic: Please Do Not Throw Sausage Pizza Away → Physical, Data Link, Network, Transport, Session, Presentation, Application.
SUBNET MENTAL MATH

IPv4 block sizes.

/24256 addresses · 254 traditional usable hosts
/25128 · 126 usable · block 128
/2664 · 62 usable · block 64
/2732 · 30 usable · block 32
/2816 · 14 usable · block 16
/298 · 6 usable · block 8
/304 · 2 usable · block 4
/32Single IPv4 address / host route
Shortcut: addresses = 2^(32-prefix). Traditional usable-host math subtracts network + broadcast where those concepts apply. /31 is a special point-to-point case.
DNS / DHCP / NAT

Core infrastructure.

AName → IPv4 address
AAAAName → IPv6 address
CNAMEAlias → canonical name
MXMail exchanger
PTRReverse lookup
NSAuthoritative name server
TXTArbitrary text; commonly verification/email policy data
DHCPDORA: Discover → Offer → Request → Acknowledge
NATTranslate address information between realms
PATMany flows can share an address using transport ports
IPv6

Stop treating it like long IPv4.

::1/128Loopback
::/128Unspecified address
fe80::/10Link-local range
2000::/3Global unicast allocation range
ff00::/8Multicast
NDPNeighbor Discovery uses ICMPv6; replaces several IPv4-era neighbor/router discovery functions
SLAACStateless Address Autoconfiguration
Compression: remove leading zeros in a hextet; one contiguous run of zero hextets may be replaced with :: once.
ROUTING / SWITCHING

Forwarding memory anchors.

SwitchPrimarily forwards Ethernet frames using MAC information
RouterForwards IP packets between networks using routes
VLANLogical Layer-2 broadcast-domain segmentation
802.1QCommon Ethernet VLAN tagging standard
STPPrevents Layer-2 switching loops
OSPFLink-state interior gateway routing protocol
BGPPath-vector routing protocol central to inter-domain routing
DefaultRoute used when no more-specific route matches
LINUX RECALL

Commands to recognize instantly.

ipAddresses, links and routes
ssSocket/listener inspection
systemctlsystemd unit lifecycle/status
journalctlsystemd journal queries
df / duFilesystem capacity / directory usage
psProcess snapshot
chmodChange file mode permissions
curlTransfer/test URLs and application endpoints
For actual workflows, jump to the Linux Field Guide from global search.
CLOUD FUNDAMENTALS

Concepts across providers.

IaaSInfrastructure building blocks: compute, networking, storage
PaaSManaged application/runtime platform
SaaSComplete application delivered as a service
RegionProvider-defined geographic deployment area
AZProvider-defined isolated location within a region; exact architecture varies
ElasticityAdjust resources with changing demand
Shared Resp.Provider and customer security/operations duties differ by service model
FLIP CARDS

Test recall before revealing.