01
CLICK THE BITSOne octet = eight bits
A bit is either 0 (off) or 1 (on). Each position doubles as you move left: 1, 2, 4 … 128.
BINARY
0100101074= sum of the switched-on weightsSTACKIT ACCESS DOMAIN · SECOND STAGE
Understand the packets,
not just the terms.
A visual crash lab for subnetting, VPNs, cloud networking, Kubernetes, and Go—built for explaining your reasoning out loud.
DAY 01AddressingCIDR · NAT · routing
DAY 02ProtocolsVPN · TCP/UDP · HTTP
DAY 03Cloud practiceK8s · Go · scenarios
REQUEST
RESPONSE
◉CLIENT10.24.8.12
◇VPN EDGEIPsec tunnel
⬡K8S10.96.0.0/12
SYN
HTTP/3
TRACE3 HOPS✓ encrypted
01 / ADDRESSING
Subnetting is just
structured counting.
Turn ambiguous address questions into four precise facts: network, broadcast, usable range, and capacity.
START HERE
Do not memorise CIDR as a magic trick. First see the address as 32 switches; then CIDR simply draws a line between the network switches and the host switches.
02
0–255 EACHIPv4 = four octets = 32 bits
10.24.8.70/26
10
0000101024
000110008
0000100070
010001102 network bits · 6 host bitsThe prefix is counted from the left. /26 means 24 full bits from the first three octets, plus 2 more bits from the last octet. The remaining 6 bits identify a host inside that subnet.
WORKED EXAMPLEPlace
256 − 192 = 64Place 10.24.8.70/26 on a number line.
1Prefix → mask
/26 means the final octet begins 11000000, which is 128 + 64 = 192. Mask: 255.255.255.192.
2Mask → block size
In the interesting octet: 256 − 192 = 64. So the possible subnet blocks begin at 0, 64, 128, 192.
3Find the block
70 sits in 64–127. Therefore the network is .64 and broadcast is .127.
4Find usable hosts
Six host bits give 2⁶ = 64 total addresses. Remove network and broadcast: 62 usable, .65–.126.
MEMORY HOOK
“Prefix is the fence; host bits are the houses.” Count host bits for capacity. Use the mask’s interesting octet for block size. Then locate the address between the block boundaries.
/
INTERACTIVECIDR range explorer
NETWORK BITSHOST BITS
#
MENTAL MODELHost-count planner
How many hosts must this subnet support?
usable hosts = 2host bits − 2Network + broadcast are reserved*✓
INTERVIEW WARM-UPSay what is valid
INTERVIEW ANSWER PATTERN
“/26 leaves 6 host bits, so it has 64 total addresses / 62 usable. Its mask is 255.255.255.192; blocks increment by 64 in the final octet.”
02 / PROTOCOL MAPS
Build a picture
before the definition.
◎
CLICK A LAYEROSI × Internet stack
07 / APPLICATION
Where user-facing protocols live.
HTTP, DNS and TLS give applications a shared language. In an interview, distinguish protocol responsibility from the physical network beneath it.
HTTP · DNS · TLS↔
TCP vs UDP
◈
VPN & routing flows
⇄
NAT translation table
03 / THE MODERN WEB
Same web.
Different transport.
04 / CLOUD REASONING
From a Pod
to the control loop.
Connect Kubernetes concepts to operational outcomes: discoverability, routing, desired state and safe convergence.
⬡
CNI MAKES IT REALKubernetes network path
Pod A10.244.1.7
→Service10.96.45.20
→kube-proxyrouting rule
→Pod B10.244.2.9
Interview lens: a Service gives a stable virtual IP; the CNI provides Pod reachability; kube-proxy (or eBPF replacement) steers Service traffic to endpoints.
↻
Operator reconciliation
{ }Go ·
Go · net/netip in one minute
05 / PRACTICE OUT LOUD
Interview
simulator.
Commit to an answer, then use the feedback as your speaking structure.
SESSION0 / 0
06 / LAST 10 MINUTES
Quick-review
cheat sheet.
CIDR
/24 = 256 addresses
Hosts = 232 − prefix − 2/26 → 62 usable
NAT
SNAT changes source for egress.
DNAT changes destination for ingress.
PAT also changes ports.
VPN
IPsec protects IP traffic.
IKEv2 negotiates SAs/keys.
ESP commonly provides encryption.
Kubernetes
Pod IPs are ephemeral.
Services are stable virtual IPs.
Operators reconcile desired state.
HTTP/3
QUIC over UDP.
Streams avoid TCP connection-level head-of-line blocking.
Fast connection setup.
Go
netip gives typed, immutable IP values.
Prefer netip.Addr / Prefix for new code.
SPRINT PROGRESS · SAVED ON THIS DEVICE
0 / 6 modules complete
YOUR DEFAULT ANSWER FRAME