# Cybersecurity (Svenska) — Avancerad (C1/C2) 1: Operating Systems, Concurrency, Networking Protocols & Distributed Systems

> [Svenska] Cybersecurity (Svenska): Processes, threads, deadlocks, virtual memory, TCP/IP, DNS, HTTP/3, Raft consensus, CAP theorem, and distributed caching

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- **Markdown URL:** https://flashcards.world/flashcards/sets/e2f74f7f-c974-4f1d-8127-3937f9c585d7.md
- **Level:** advanced
- **Languages:** sv → sv
- **Total Cards:** 32

## Flashcards (32 Cards)

| # | Front (Term / Prompt) | Back (Definition / Answer) | Example | Multiple-Choice Options |
| :--- | :--- | :--- | :--- | :--- |
| 1 | What problem does HTTP/2 solve over HTTP/1.1, and what is its binary framing mechanism? | Eliminates HTTP application head-of-line blocking by multiplexing multiple independent bidirectional streams over a single TCP connection using binary framing (HEADERS and DATA frames) and HPACK header compression. |  |  |
| 2 | How does the Cache-Aside (Lazy Loading) caching pattern function? | The application first checks the cache: on a hit, it returns the cached data; on a miss, it reads from the database, writes the fetched data into the cache, and returns it. |  |  |
| 3 | How does TCP Congestion Control transition between Slow Start and Congestion Avoidance? | During Slow Start, cwnd doubles every RTT (exponential growth) until it reaches the slow start threshold (ssthresh), where it switches to Congestion Avoidance, increasing cwnd by 1 MSS per RTT (additive increase). |  |  |
| 4 | What does the PACELC theorem state extending the CAP theorem? | If there is a Partition (P), choose Availability (A) or Consistency (C); Else (E), choose Latency (L) or Consistency (C). |  |  |
| 5 | Compare Write-Through and Write-Back (Write-Behind) distributed caching patterns. | Write-Through synchronously writes to cache and database simultaneously (high durability, higher write latency); Write-Back writes immediately to cache and queues asynchronous batch writes to database (low latency, risk of data loss on crash). |  |  |
| 6 | What is the Cache Stampede (Thundering Herd) problem, and how is it prevented? | Occurs when a popular cached key expires, causing massive concurrent requests to hit the database simultaneously; prevented by distributed mutex locking (single flight) or probabilistic early expiration (XFetch). |  |  |
| 7 | State the CAP Theorem and explain the operational trade-off required during a network partition. | A distributed system can guarantee at most two of Consistency, Availability, and Partition Tolerance; because network partitions (P) are unavoidable, systems must choose between Consistency (CP, failing unavailable requests) or Availability (AP, returning stale data). |  |  |
| 8 | How does Transport Layer Security (TLS 1.3) establish confidentiality and integrity? | Uses Diffie-Hellman (ECDHE) for ephemeral asymmetric key exchange to provide forward secrecy, authenticates server via X.509 certificates, and encrypts payload with symmetric authenticated ciphers (AEAD like AES-GCM or ChaCha20-Poly1305). |  |  |
| 9 | What information is saved and restored during an operating system context switch? | CPU hardware registers, program counter (PC), stack pointer, processor status flags, and memory management registers (CR3/page table pointer in PCB). |  |  |
| 10 | In the Raft consensus algorithm, how does leader election work, and what role do randomized election timeouts play? | If a follower receives no heartbeat, it becomes a Candidate and requests votes; randomized timeouts (e.g., 150–300 ms) prevent split votes by ensuring one candidate typically times out and wins a majority vote first. |  |  |
| 11 | Describe the packets exchanged during the TCP Three-Way Handshake connection establishment. | 1. Client sends SYN (with client initial sequence number ISN_c). 2. Server replies with SYN-ACK (ISN_s and ACK = ISN_c + 1). 3. Client sends ACK (ACK = ISN_s + 1). |  |  |
| 12 | What sequential steps occur when an instruction triggers a page fault exception in the CPU? | 1. MMU detects unmapped PTE and raises page fault trap. 2. OS locates frame on disk swap. 3. OS reads disk page into a free physical frame. 4. OS updates PTE with valid bit and physical frame number. 5. OS restarts the faulting instruction. |  |  |
| 13 | How does the Two-Phase Commit (2PC) protocol ensure atomic distributed transactions across multiple nodes? | Phase 1 (Prepare): Coordinator asks all cohorts to prepare and vote YES/NO; Phase 2 (Commit): If all voted YES, coordinator writes commit and broadcasts COMMIT; if any voted NO or timed out, broadcasts ABORT. |  |  |
| 14 | What is the Raft Log Matching property, and how does the leader enforce it? | If two logs contain an entry with the same index and term, they are identical up to that index; the leader overwrites conflicting uncommitted follower entries with its own log entries. |  |  |
| 15 | What is Eventual Consistency in distributed systems, and what ensures that replicas eventually converge? | If no new updates are made, all replicas will eventually return identical values; convergence is achieved using conflict resolution protocols like vector clocks, CRDTs, or Last-Write-Wins (LWW). |  |  |
| 16 | What is virtual memory paging, and what hardware component accelerates virtual-to-physical address translation? | Dividing virtual and physical memory into fixed-size blocks (pages and frames) mapped via page tables; accelerated by the Translation Lookaside Buffer (TLB), an on-chip associative cache. |  |  |
| 17 | What is the Circuit Breaker pattern in microservices distributed architectures? | A pattern with three states: Closed (requests pass through), Open (failures exceed threshold, calls fail fast without hitting dependency), and Half-Open (trial requests test if service has recovered). |  |  |
| 18 | Why does the active closer in a TCP connection enter the TIME_WAIT state for 2*MSL (Maximum Segment Lifetime)? | To ensure the final ACK is reliably delivered to the remote peer (resending if lost) and to allow stale duplicate packets in the network to expire before socket reuse. |  |  |
| 19 | Compare the 7 layers of the OSI model with the 4 layers of the TCP/IP model. | OSI: Physical, Data Link, Network, Transport, Session, Presentation, Application. TCP/IP: Network Interface (Link), Internet, Transport, Application. |  |  |
| 20 | Why was HTTP/3 developed to run over QUIC (UDP) rather than TCP? | In HTTP/2 over TCP, a single dropped packet stalls all multiplexed streams (TCP head-of-line blocking); QUIC runs over UDP and handles independent packet recovery per stream with 0-RTT/1-RTT connection setup. |  |  |
| 21 | How does Consistent Hashing minimize key redistribution when server nodes are added or removed? | Hashes both keys and nodes to positions on a 360° circular hash ring; a key is assigned to the next clockwise node; adding or removing a node only moves keys in its immediate adjacent partition (O(K/N) keys moved). |  |  |
| 22 | How does TCP sliding window flow control prevent a sender from overwhelming a receiver? | The receiver advertises its available buffer capacity in the TCP header Receive Window (rwnd) field; the sender limits in-flight unacknowledged bytes to min(cwnd, rwnd). |  |  |
| 23 | What are the key operational differences between TCP and UDP at the transport layer? | TCP is connection-oriented, provides guaranteed delivery, ordered streams, error recovery, flow and congestion control; UDP is connectionless, unordered, lightweight, with minimal overhead and no retransmissions. |  |  |
| 24 | What is Belady's anomaly in operating system page replacement? | The counterintuitive phenomenon where increasing the number of physical page frames results in more page faults, occurring in FIFO page replacement (impossible in stack algorithms like LRU). |  |  |
| 25 | What is the fundamental difference between an operating system process and a thread? | A process has an independent virtual address space, file descriptors, and security context; threads within the same process share the process address space, heap, and code, but have private registers and stacks. |  |  |
| 26 | How does a Mutex differ from a Counting Semaphore? | A Mutex provides mutual exclusion with thread ownership (only the thread that locked it can unlock it); a counting semaphore is an atomic signaling counter (sem_wait/sem_post) permitting up to N concurrent threads without ownership. |  |  |
| 27 | What is a race condition, and what defines a critical section in concurrent programming? | A race condition occurs when concurrent thread output depends on non-deterministic execution timing; a critical section is a code block accessing shared mutable state that must not be concurrently executed. |  |  |
| 28 | How does Preemptive Round-Robin CPU scheduling function, and what trade-off governs time quantum selection? | Each ready process receives a fixed time slice (quantum); if too large, responsiveness degrades to FCFS; if too small, CPU context switching overhead degrades throughput. |  |  |
| 29 | Trace the recursive DNS resolution process for resolving a new domain name (e.g., example.com). | Client queries Recursive Resolver -> Root DNS server (returns .com TLD server) -> TLD server (returns authoritative nameserver for example.com) -> Authoritative Nameserver (returns A/AAAA record) -> Resolver caches and returns IP to client. |  |  |
| 30 | What are the four Coffman conditions necessary and sufficient for a deadlock to occur? | 1. Mutual Exclusion 2. Hold and Wait 3. No Preemption 4. Circular Wait. |  |  |
| 31 | How can deadlock be prevented by eliminating the Circular Wait condition? | Impose a global total ordering on all lockable resources and require every thread to acquire locks strictly in increasing numerical order. |  |  |
| 32 | What is the critical failure mode of the Two-Phase Commit (2PC) protocol? | It is a blocking protocol: if the coordinator crashes during Phase 2 after cohorts have voted YES, cohorts remain indefinitely blocked holding locks, unable to abort or commit autonomously. |  |  |

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