1. What is a computer network?
A system of interconnected devices, e.g., computers, routers, sharing data.
2. What is the OSI model?
A 7-layer framework, e.g., Physical, Data Link, Network, Transport, Session, Presentation, Application.
3. What is the TCP/IP model?
A 4-layer model, e.g., Link, Internet, Transport, Application, used in practice.
4. What is the purpose of the Physical layer in OSI?
Handles physical connections, e.g., cables, signals, bit transmission.
5. What does the Data Link layer do?
Manages node-to-node data transfer, e.g., Ethernet, MAC addresses.
6. What is the Network layer responsible for?
Handles routing, e.g., IP addressing, packet forwarding.
7. What is the Transport layer\'s role?
Ensures reliable data transfer, e.g., TCP, UDP, port numbers.
8. What does the Session layer do?
Manages sessions, e.g., establishing, maintaining connections.
9. What is the Presentation layer?
Translates data formats, e.g., encryption, compression.
10. What does the Application layer do?
Provides network services to apps, e.g., HTTP, FTP.
11. What is an IP address?
A unique identifier for devices, e.g., 192.168.1.1 (IPv4).
12. What is the difference between IPv4 and IPv6?
IPv4 uses 32 bits (e.g., 192.168.1.1); IPv6 uses 128 bits (e.g., 2001:0db8::1).
13. What is a MAC address?
A unique hardware identifier, e.g., 00:1A:2B:3C:4D:5E, used at Data Link layer.
14. What is a subnet?
A divided network segment, e.g., 192.168.1.0/24.
15. What is a subnet mask?
Defines network portion, e.g., 255.255.255.0 for /24.
16. How do you calculate hosts in a subnet?
2^(32-CIDR)-2, e.g., /24 gives 254 hosts (256-2 for network, broadcast).
17. What is CIDR notation?
IP address with prefix length, e.g., 192.168.1.0/24.
18. What is a gateway?
A device routing traffic, e.g., default gateway 192.168.1.1.
19. What is a router?
A device forwarding packets between networks, e.g., connects LAN to WAN.
20. What is a switch?
A device connecting devices in a LAN, e.g., forwards frames using MAC addresses.
21. What is a hub?
A basic device broadcasting data to all ports, e.g., less efficient than switch.
22. What is a LAN?
Local Area Network, e.g., office network, typically small scale.
23. What is a WAN?
Wide Area Network, e.g., the internet, connects multiple LANs.
24. What is a VLAN?
Virtual LAN, e.g., segments network logically without separate hardware.
25. What is a packet?
A unit of data, e.g., includes header, payload, sent over network.
26. What is a frame?
Data Link layer unit, e.g., Ethernet frame with MAC addresses.
27. What is a segment in networking?
Transport layer unit, e.g., TCP segment with port numbers.
28. What is bandwidth?
Data transfer capacity, e.g., 100 Mbps.
29. What is latency?
Time delay in data transfer, e.g., 20 ms ping.
30. What is throughput?
Actual data transfer rate, e.g., 80 Mbps on a 100 Mbps link.
31. What is jitter?
Variation in latency, e.g., inconsistent packet delays.
32. What is a broadcast?
Sends data to all devices, e.g., ARP broadcast in subnet.
33. What is a multicast?
Sends data to specific group, e.g., video streaming.
34. What is a unicast?
Sends data to one device, e.g., HTTP request.
35. What is the difference between half-duplex and full-duplex?
Half-duplex: one-way at a time (e.g., walkie-talkie); full-duplex: simultaneous (e.g., phone).
36. What is a port in networking?
A logical endpoint, e.g., 80 for HTTP, 443 for HTTPS.
37. What is NAT?
Network Address Translation, e.g., maps private IPs to public IP.
38. What is a private IP address?
Non-routable IPs, e.g., 192.168.0.0/16, 10.0.0.0/8.
39. What is a public IP address?
Globally routable, e.g., 8.8.8.8 (Google DNS).
40. What is APIPA?
Automatic Private IP Addressing, e.g., 169.254.0.0/16 when DHCP fails.
41. What is a static IP address?
Manually assigned, e.g., 192.168.1.100 for a server.
42. What is a dynamic IP address?
Assigned by DHCP, e.g., changes over time.
43. What is a loopback address?
Tests local network, e.g., 127.0.0.1 (localhost).
44. What is a collision in networking?
Data overlap in shared medium, e.g., Ethernet hub.
45. What is CSMA/CD?
Carrier Sense Multiple Access/Collision Detection, e.g., Ethernet collision handling.
46. What is an Ethernet cable?
Physical medium, e.g., Cat5e, Cat6 for LAN connections.
47. What is the difference between Cat5e and Cat6?
Cat5e: up to 1 Gbps; Cat6: up to 10 Gbps, less crosstalk.
48. What is a crossover cable?
Connects similar devices, e.g., PC-to-PC, swaps TX/RX pairs.
49. What is a straight-through cable?
Connects different devices, e.g., PC-to-switch.
50. What is fiber optic cabling?
Uses light, e.g., high-speed, long-distance, immune to EMI.
51. What is a network interface card (NIC)?
Connects device to network, e.g., Ethernet or Wi-Fi card.
52. What is a wireless access point (WAP)?
Enables Wi-Fi connections, e.g., extends LAN wirelessly.
53. What is SSID?
Wi-Fi network name, e.g., \"MyWiFi\".
54. What is a network topology?
Layout of network, e.g., star, bus, ring.
55. What is a star topology?
Devices connect to central hub, e.g., common in LANs.
56. What is a bus topology?
Devices share single cable, e.g., older Ethernet.
57. What is a ring topology?
Devices form a loop, e.g., token ring networks.
58. What is a mesh topology?
Devices interconnect, e.g., high redundancy.
59. What is QoS?
Quality of Service, e.g., prioritizes traffic like VoIP.
60. What is a collision domain?
Network segment where collisions occur, e.g., hub-based Ethernet.
61. What is a broadcast domain?
Network segment for broadcasts, e.g., separated by routers.
62. What is MTU?
Maximum Transmission Unit, e.g., 1500 bytes for Ethernet.
63. What is a network protocol?
Rules for communication, e.g., TCP, IP, HTTP.
64. What is encapsulation?
Wrapping data with headers, e.g., TCP segment in IP packet.
65. What is de-encapsulation?
Removing headers, e.g., extracting TCP segment from IP packet.
66. What is a network segment?
A portion of network, e.g., separated by switch or router.
67. What is a proxy server?
Intermediary for requests, e.g., caches web content.
68. What is a reverse proxy?
Handles client requests for servers, e.g., load balancing.
69. What is a DMZ?
Demilitarized Zone, e.g., isolated subnet for public-facing servers.
70. // Protocols and Services: What is TCP?
Transmission Control Protocol, e.g., reliable, connection-oriented.
71. What is UDP?
User Datagram Protocol, e.g., fast, connectionless.
72. What is the difference between TCP and UDP?
TCP: reliable, ordered; UDP: faster, no error checking.
73. What is HTTP?
Hypertext Transfer Protocol, e.g., web browsing, port 80.
74. What is HTTPS?
Secure HTTP, e.g., uses SSL/TLS, port 443.
75. What is FTP?
File Transfer Protocol, e.g., file sharing, ports 20/21.
76. What is SFTP?
Secure FTP, e.g., uses SSH, port 22.
77. What is DNS?
Domain Name System, e.g., resolves example.com to 93.184.216.34.
78. What is DHCP?
Dynamic Host Configuration Protocol, e.g., assigns IPs automatically.
79. What is ICMP?
Internet Control Message Protocol, e.g., used by ping.
80. What is ARP?
Address Resolution Protocol, e.g., maps IP to MAC.
81. What is RARP?
Reverse ARP, e.g., maps MAC to IP (older protocol).
82. What is SNMP?
Simple Network Management Protocol, e.g., monitors devices.
83. What is SMTP?
Simple Mail Transfer Protocol, e.g., sends emails, port 25.
84. What is IMAP?
Internet Message Access Protocol, e.g., retrieves emails, port 143.
85. What is POP3?
Post Office Protocol, e.g., downloads emails, port 110.
86. What is Telnet?
Remote terminal access, e.g., port 23, unencrypted.
87. What is SSH?
Secure Shell, e.g., encrypted remote access, port 22.
88. What is NTP?
Network Time Protocol, e.g., synchronizes clocks, port 123.
89. What is BGP?
Border Gateway Protocol, e.g., routes between autonomous systems.
90. What is OSPF?
Open Shortest Path First, e.g., link-state routing protocol.
91. What is RIP?
Routing Information Protocol, e.g., distance-vector routing.
92. What is IGMP?
Internet Group Management Protocol, e.g., manages multicast groups.
93. What is SIP?
Session Initiation Protocol, e.g., VoIP signaling.
94. What is RTP?
Real-time Transport Protocol, e.g., streams audio/video.
95. What is GRE?
Generic Routing Encapsulation, e.g., tunnels packets.
96. What is IPsec?
Internet Protocol Security, e.g., secures IP communications.
97. What is PPP?
Point-to-Point Protocol, e.g., used in VPNs, dial-up.
98. What is L2TP?
Layer 2 Tunneling Protocol, e.g., VPN tunneling.
99. What is MPLS?
Multiprotocol Label Switching, e.g., fast packet forwarding.
100. What is DNS A record?
Maps hostname to IPv4, e.g., example.com to 93.184.216.34.
101. What is a DNS CNAME record?
Aliases hostname, e.g., www.example.com to example.com.
102. What is a DNS MX record?
Specifies mail server, e.g., mail.example.com for email.
103. What is a DNS PTR record?
Reverse lookup, e.g., IP to hostname.
104. What is a DNS SOA record?
Start of Authority, e.g., zone metadata.
105. What is a DNS TTL?
Time to Live, e.g., caching duration in seconds.
106. What is a TCP handshake?
Three-way process, e.g., SYN, SYN-ACK, ACK.
107. What is TCP windowing?
Controls data flow, e.g., adjusts data sent before ACK.
108. What is TCP congestion control?
Manages network load, e.g., slow start, congestion avoidance.
109. What is a socket?
Endpoint for communication, e.g., IP:port pair.
110. What is a well-known port?
Ports 0-1023, e.g., 80 for HTTP, assigned by IANA.
111. What is an ephemeral port?
Temporary port, e.g., 49152-65535 for client connections.
112. What is HTTP GET?
Requests data, e.g., retrieves webpage.
113. What is HTTP POST?
Sends data, e.g., submits form.
114. What is HTTP status code 200?
OK, e.g., request successful.
115. What is HTTP status code 404?
Not Found, e.g., resource missing.
116. What is HTTP status code 500?
Internal Server Error, e.g., server failure.
117. What is a DHCP lease?
IP assignment duration, e.g., 24 hours.
118. What is a DHCP relay?
Forwards DHCP requests, e.g., across subnets.
119. What is a DNS resolver?
Client-side DNS, e.g., queries DNS server.
120. What is a root DNS server?
Top-level DNS, e.g., resolves TLDs like .com.
121. What is a TLD?
Top-Level Domain, e.g., .com, .org.
122. What is a DNS zone?
Portion of namespace, e.g., example.com managed by one server.
123. What is a DNS forwarder?
Relays DNS queries, e.g., to upstream server.
124. What is a TCP flag?
Controls connection, e.g., SYN, ACK, FIN.
125. What is a SYN flood?
DoS attack, e.g., sends many SYN packets.
126. What is a UDP flood?
DoS attack, e.g., overwhelms with UDP packets.
127. What is a ping of death?
DoS attack, e.g., oversized ICMP packets (older systems).
128. What is a protocol analyzer?
Tool for packet inspection, e.g., Wireshark.
129. What is a VPN?
Virtual Private Network, e.g., secure tunnel over internet.
130. What is OpenVPN?
Open-source VPN, e.g., uses SSL/TLS.
131. What is WireGuard?
Modern VPN, e.g., lightweight, fast, secure.
132. What is a proxy ARP?
Router responds to ARP, e.g., for devices without ARP.
133. What is a TCP keepalive?
Checks connection, e.g., periodic probes.
134. What is a jumbo frame?
Large Ethernet frame, e.g., 9000 bytes for performance.
135. // Network Configuration and Tools: What is the `ifconfig` command?
Configures interfaces, e.g., `ifconfig eth0 192.168.1.2` (older).
136. What is the `ip` command?
Modern tool, e.g., `ip addr show` for interfaces.
137. What does the `ping` command do?
Tests connectivity, e.g., `ping 8.8.8.8`.
138. What is the `traceroute` command?
Shows packet path, e.g., `traceroute google.com`.
139. What is the `netstat` command?
Shows network stats, e.g., `netstat -tuln` for listening ports.
140. What does the `ss` command do?
Modern `netstat`, e.g., `ss -tuln` for sockets.
141. What is the `dig` command?
Queries DNS, e.g., `dig example.com`.
142. What does the `nslookup` command do?
Resolves DNS, e.g., `nslookup example.com`.
143. What is the `curl` command?
Fetches URLs, e.g., `curl http://example.com`.
144. What does the `wget` command do?
Downloads files, e.g., `wget http://example.com/file`.
145. What is the `tcpdump` command?
Captures packets, e.g., `tcpdump -i eth0`.
146. What does the `ethtool` command do?
Manages NICs, e.g., `ethtool eth0` for status.
147. What is the `route` command?
Shows routing table, e.g., `route -n`.
148. What does the `ip route` command do?
Manages routes, e.g., `ip route add default via 192.168.1.1`.
149. What is the `arp` command?
Shows ARP table, e.g., `arp -n`.
150. What does the `nmcli` command do?
Manages NetworkManager, e.g., `nmcli con show`.
151. What is the `iwconfig` command?
Configures wireless, e.g., `iwconfig wlan0` (older).
152. What does the `iw` command do?
Modern wireless tool, e.g., `iw dev wlan0 scan`.
153. What is the `/etc/hosts` file?
Maps hostnames to IPs, e.g., `127.0.0.1 localhost`.
154. What is the `/etc/resolv.conf` file?
Configures DNS, e.g., `nameserver 8.8.8.8`.
155. What does the `hostname` command do?
Shows/sets hostname, e.g., `hostname myhost`.
156. What is the `/etc/hostname` file?
Stores hostname, e.g., `echo myhost > /etc/hostname`.
157. What does the `mtr` command do?
Combines ping/traceroute, e.g., `mtr google.com`.
158. What is the `nc` command?
Network tool, e.g., `nc -l 12345` to listen.
159. What does the `telnet` command do?
Tests connections, e.g., `telnet localhost 80`.
160. What is the `iftop` command?
Shows bandwidth usage, e.g., `iftop -i eth0`.
161. What does the `nethogs` command do?
Shows bandwidth by process, e.g., `nethogs eth0`.
162. What is the `vnstat` command?
Monitors traffic, e.g., `vnstat -i eth0`.
163. What does the `iptraf` command do?
Monitors traffic, e.g., `iptraf-ng`.
164. What is the `bmon` command?
Bandwidth monitor, e.g., `bmon`.
165. What does the `hping3` command do?
Packet crafting, e.g., `hping3 -S host` for SYN scan.
166. What is the `whois` command?
Queries domain info, e.g., `whois example.com`.
167. What does the `nmap` command do?
Scans network, e.g., `nmap localhost` for open ports.
168. What is the `ip addr` command?
Shows/configures IPs, e.g., `ip addr add 192.168.1.2/24 dev eth0`.
169. What does the `ip link` command do?
Manages interfaces, e.g., `ip link set eth0 up`.
170. What is the `ip neighbor` command?
Shows ARP cache, e.g., `ip neighbor show`.
171. What does the `brctl` command do?
Manages bridges, e.g., `brctl addbr br0`.
172. What is the `conntrack` command?
Manages connection tracking, e.g., `conntrack -L`.
173. What does the `dnsmasq` command do?
Provides DNS/DHCP, e.g., `dnsmasq --no-daemon`.
174. What is the `/etc/network/interfaces` file?
Configures interfaces (Debian), e.g., `auto eth0`, `iface eth0 inet static`.
175. What does the `systemctl restart networking` command do?
Restarts networking, e.g., applies interface changes (Debian).
176. What is the `NetworkManager` service?
Manages network configs, e.g., GUI/CLI tool for dynamic networks.
177. What does the `rfkill` command do?
Manages wireless, e.g., `rfkill unblock wifi`.
178. What is the `ipset` command?
Manages IP sets, e.g., `ipset create myset hash:ip`.
179. What does the `tc` command do?
Traffic control, e.g., `tc qdisc add dev eth0 root netem delay 100ms`.
180. What is the `ipvsadm` command?
Manages IPVS, e.g., `ipvsadm -A -t 192.168.1.1:80`.
181. What does the `ethtool -S` command do?
Shows NIC stats, e.g., `ethtool -S eth0` for packet counts.
182. What is the `ip monitor` command?
Monitors changes, e.g., `ip monitor all`.
183. What does the `socat` command do?
Multiplexes sockets, e.g., `socat TCP-LISTEN:12345 TCP:localhost:22`.
184. What is the `iperf` command?
Measures bandwidth, e.g., `iperf -s` (server), `iperf -c host` (client).
185. What does the `nload` command do?
Shows network usage, e.g., `nload eth0`.
186. What is the `bwm-ng` command?
Monitors bandwidth, e.g., `bwm-ng`.
187. What does the `ipcalc` command do?
Calculates subnets, e.g., `ipcalc 192.168.1.0/24`.
188. What is the `arping` command?
Pings via ARP, e.g., `arping 192.168.1.1`.
189. What does the `ip link set mtu` command do?
Sets MTU, e.g., `ip link set eth0 mtu 9000`.
190. What is the `ip tuntap` command?
Manages TUN/TAP, e.g., `ip tuntap add dev tun0 mode tun`.
191. What does the `ip netns` command do?
Manages network namespaces, e.g., `ip netns add myns`.
192. What is the `iwlist` command?
Scans Wi-Fi, e.g., `iwlist wlan0 scan` (older).
193. What does the `ip route get` command do?
Shows route for destination, e.g., `ip route get 8.8.8.8`.
194. What is the `ip rule` command?
Manages policy routing, e.g., `ip rule add from 192.168.1.0/24 lookup 100`.
195. What does the `ip maddr` command do?
Manages multicast, e.g., `ip maddr show dev eth0`.
196. What is the `ip xfrm` command?
Manages IPsec, e.g., `ip xfrm state list`.
197. What does the `ethtool -k` command do?
Shows offload settings, e.g., `ethtool -k eth0`.
198. What is the `ip -s link` command?
Shows interface stats, e.g., `ip -s link show eth0`.
199. // Routing and Switching: What is routing?
Forwarding packets between networks, e.g., using routing tables.
200. What is a routing table?
Maps destinations to next hops, e.g., `ip route show`.
201. What is a default route?
Catch-all route, e.g., `0.0.0.0/0 via 192.168.1.1`.
202. What is a static route?
Manually configured, e.g., `ip route add 10.0.0.0/8 via 192.168.1.2`.
203. What is a dynamic route?
Learned via protocols, e.g., OSPF, BGP.
204. What is a routing protocol?
Exchanges routing info, e.g., RIP, OSPF, BGP.
205. What is an IGP?
Interior Gateway Protocol, e.g., OSPF, RIP within AS.
206. What is an EGP?
Exterior Gateway Protocol, e.g., BGP between ASes.
207. What is an Autonomous System (AS)?
A network under one admin, e.g., ISP with unique ASN.
208. What is BGP convergence?
Time to stabilize routes, e.g., after topology change.
209. What is OSPF area?
Logical grouping, e.g., Area 0 (backbone).
210. What is a Designated Router (DR) in OSPF?
Reduces updates, e.g., elected on multi-access network.
211. What is a link-state database in OSPF?
Stores topology, e.g., used for SPF calculation.
212. What is RIP\'s maximum hop count?
15, e.g., prevents routing loops.
213. What is a route metric?
Cost to destination, e.g., hop count, bandwidth.
214. What is policy-based routing?
Routes based on rules, e.g., `ip rule add from 192.168.1.0/24 lookup 100`.
215. What is a switching table?
Maps MACs to ports, e.g., switch’s forwarding database.
216. What is a VLAN tag?
Identifies VLAN, e.g., 802.1Q tag in Ethernet frame.
217. What is VLAN trunking?
Carries multiple VLANs, e.g., tagged frames on link.
218. What is 802.1Q?
VLAN tagging standard, e.g., adds 4-byte tag.
219. What is a native VLAN?
Untagged VLAN, e.g., default on trunk.
220. What is Spanning Tree Protocol (STP)?
Prevents loops, e.g., blocks redundant paths.
221. What is a Root Bridge in STP?
Central switch, e.g., lowest bridge ID.
222. What is RSTP?
Rapid STP, e.g., faster convergence than STP.
223. What is a BPDU?
Bridge Protocol Data Unit, e.g., STP control messages.
224. What is portfast in STP?
Skips listening/learning, e.g., for end devices.
225. What is EtherChannel?
Bundles links, e.g., LACP for redundancy, bandwidth.
226. What is LACP?
Link Aggregation Control Protocol, e.g., negotiates EtherChannel.
227. What is a MAC address table overflow?
Attack flooding table, e.g., causes switch to flood.
228. What is port security?
Restricts MACs, e.g., limits devices on switch port.
229. What is a VTP?
VLAN Trunking Protocol, e.g., synchronizes VLANs.
230. What is a VTP pruning?
Reduces VLAN traffic, e.g., only sends needed VLANs.
231. What is a switchport mode access?
Assigns single VLAN, e.g., for end devices.
232. What is a switchport mode trunk?
Carries multiple VLANs, e.g., for inter-switch links.
233. What is HSRP?
Hot Standby Router Protocol, e.g., virtual IP for redundancy.
234. What is VRRP?
Virtual Router Redundancy Protocol, e.g., similar to HSRP.
235. What is GLBP?
Gateway Load Balancing Protocol, e.g., load balances gateways.
236. What is a multilayer switch?
Switches and routes, e.g., supports VLANs, IP routing.
237. What is a routing loop?
Packets cycle indefinitely, e.g., prevented by TTL.
238. What is split horizon?
Prevents loops, e.g., don’t advertise route back to source.
239. What is route poisoning?
Marks route unreachable, e.g., RIP sets metric to 16.
240. What is a floating static route?
Backup route, e.g., higher administrative distance.
241. What is administrative distance?
Route preference, e.g., static (1), OSPF (110), BGP (20).
242. What is a next-hop?
Next router, e.g., `ip route 10.0.0.0/8 via 192.168.1.2`.
243. What is a blackhole route?
Discards traffic, e.g., `ip route 10.0.0.0/8 null0`.
244. What is a route summarization?
Combines routes, e.g., 192.168.1.0/24, 192.168.2.0/24 to 192.168.0.0/22.
245. What is ECMP?
Equal-Cost Multi-Path, e.g., load balances over equal-cost routes.
246. What is a switch virtual interface (SVI)?
VLAN interface, e.g., `interface vlan 10` for routing.
247. What is a routed port?
Switch port as layer 3, e.g., `no switchport` on interface.
248. What is a QinQ?
Double VLAN tagging, e.g., 802.1Q-in-802.1Q.
249. What is a private VLAN?
Isolates ports in VLAN, e.g., primary, isolated, community.
250. What is a MAC-based VLAN?
Assigns VLAN by MAC, e.g., for dynamic assignment.
251. What is a voice VLAN?
Prioritizes VoIP, e.g., separate VLAN for phones.
252. What is a dynamic VLAN?
Assigned via protocol, e.g., VMPS or RADIUS.
253. What is a loopback interface?
Virtual interface, e.g., `interface loopback 0` for routing.
254. What is a tunnel interface?
Virtual link, e.g., GRE or IPsec tunnel.
255. What is a LAG?
Link Aggregation Group, e.g., bundles ports for bandwidth.
256. What is a PoE switch?
Power over Ethernet, e.g., powers IP phones, cameras.
257. What is a managed switch?
Configurable switch, e.g., supports VLANs, QoS.
258. What is an unmanaged switch?
Plug-and-play, e.g., no configuration options.
259. // Network Security: What is a firewall?
Filters traffic, e.g., based on rules for ports, IPs.
260. What is a stateful firewall?
Tracks connections, e.g., allows return traffic.
261. What is a stateless firewall?
Filters per packet, e.g., no connection tracking.
262. What is the `iptables` command?
Configures Linux firewall, e.g., `iptables -A INPUT -p tcp --dport 22 -j ACCEPT`.
263. What is the `ufw` command?
Simplifies firewall, e.g., `ufw allow 22`.
264. What does the `firewalld` command do?
Manages firewall, e.g., `firewall-cmd --add-port
265. What is the `nft` command?
Manages nftables, e.g., `nft add rule ip filter input accept`.
266. What is a DMZ in security?
Isolated subnet, e.g., for public-facing servers.
267. What is a VPN in security?
Encrypts traffic, e.g., IPsec, OpenVPN.
268. What is SSL/TLS?
Encrypts data, e.g., secures HTTPS, port 443.
269. What is a certificate authority (CA)?
Issues SSL certificates, e.g., Let’s Encrypt.
270. What is a self-signed certificate?
Self-generated certificate, e.g., not trusted by browsers.
271. What is a public key infrastructure (PKI)?
Manages keys, certificates, e.g., for SSL/TLS.
272. What is a man-in-the-middle (MITM) attack?
Intercepts communication, e.g., spoofing HTTPS.
273. What is ARP spoofing?
Fakes MAC address, e.g., redirects traffic.
274. What is DNS spoofing?
Fakes DNS responses, e.g., redirects to malicious site.
275. What is a DDoS attack?
Overwhelms resources, e.g., floods with traffic.
276. What is a SYN flood attack?
Exploits TCP handshake, e.g., sends many SYN packets.
277. What is an IDS?
Intrusion Detection System, e.g., monitors for suspicious activity.
278. What is an IPS?
Intrusion Prevention System, e.g., blocks threats.
279. What is Snort?
Open-source IDS/IPS, e.g., analyzes packets.
280. What is a WAF?
Web Application Firewall, e.g., protects against SQL injection.
281. What is a packet filter?
Blocks packets by rules, e.g., based on IP, port.
282. What is a proxy firewall?
Intercepts application traffic, e.g., inspects HTTP.
283. What is a NAT firewall?
Uses NAT to hide IPs, e.g., blocks unsolicited inbound.
284. What is a VPN concentrator?
Handles VPN connections, e.g., for remote users.
285. What is a bastion host?
Hardened server, e.g., single entry point to network.
286. What is port knocking?
Hides ports, e.g., opens after specific sequence.
287. What is a honeypot?
Decoy system, e.g., attracts attackers for monitoring.
288. What is a honeynet?
Network of honeypots, e.g., simulates real environment.
289. What is MAC filtering?
Allows/denies devices by MAC, e.g., on Wi-Fi.
290. What is 802.1X?
Port-based authentication, e.g., RADIUS for network access.
291. What is RADIUS?
Remote Authentication Dial-In User Service, e.g., centralizes auth.
292. What is TACACS+?
Terminal Access Controller Access-Control System, e.g., device auth.
293. What is Kerberos?
Authentication protocol, e.g., ticket-based for networks.
294. What is a VLAN hopping attack?
Accesses other VLANs, e.g., double tagging.
295. What is a MAC spoofing attack?
Fakes MAC address, e.g., bypasses port security.
296. What is a session hijacking?
Steals session, e.g., captures cookies.
297. What is a brute force attack?
Tries many passwords, e.g., targets SSH.
298. What is a dictionary attack?
Uses wordlist, e.g., guesses common passwords.
299. What is a rainbow table attack?
Uses precomputed hashes, e.g., cracks passwords.
300. What is a zero-day exploit?
Attacks unknown vulnerability, e.g., before patch.
301. What is a firewall zone?
Logical grouping, e.g., `firewalld` public, trusted zones.
302. What is a security group?
Cloud firewall rules, e.g., AWS controls instance traffic.
303. What is a network ACL?
Subnet-level rules, e.g., stateless in AWS VPC.
304. What is a VPN split tunneling?
Routes some traffic via VPN, e.g., only corporate traffic.
305. What is a VPN kill switch?
Blocks traffic if VPN drops, e.g., prevents leaks.
306. What is a GRE tunnel?
Encapsulates packets, e.g., unencrypted tunnel.
307. What is a site-to-site VPN?
Connects networks, e.g., branch to HQ.
308. What is a remote access VPN?
Connects users, e.g., employee to corporate network.
309. What is a DMZ host?
Exposes one device, e.g., web server to internet.
310. What is a content filter?
Blocks websites, e.g., by category or URL.
311. What is a sandbox in security?
Isolates threats, e.g., runs malware safely.
312. What is a secure enclave?
Isolated processing, e.g., hardware-based security.
313. What is a trusted platform module (TPM)?
Hardware for crypto, e.g., stores keys.
314. What is a hardware security module (HSM)?
Dedicated crypto device, e.g., for key management.
315. What is a network tap?
Monitors traffic, e.g., mirrors packets to analyzer.
316. What is a port mirror?
Copies port traffic, e.g., for monitoring.
317. What is a VLAN ACL (VACL)?
Filters VLAN traffic, e.g., within switch.
318. What is a dynamic ARP inspection (DAI)?
Prevents ARP spoofing, e.g., validates ARP packets.
319. What is DHCP snooping?
Prevents rogue DHCP, e.g., filters untrusted ports.
320. What is a secure boot?
Verifies firmware, e.g., prevents unauthorized OS.
321. What is a network segmentation?
Divides network, e.g., VLANs for security.
322. // Troubleshooting and Monitoring: What is packet loss?
Dropped packets, e.g., due to congestion.
323. What is high latency?
Increased delay, e.g., slow network response.
324. What is a network bottleneck?
Resource limitation, e.g., low bandwidth link.
325. What is Wireshark?
Packet analyzer, e.g., captures, filters traffic.
326. What does the `tcpdump` command do for troubleshooting?
Captures packets, e.g., `tcpdump -i eth0 port 80`.
327. What is the `ping` command for troubleshooting?
Tests reachability, e.g., `ping -c 4 8.8.8.8`.
328. What does the `traceroute` command do for troubleshooting?
Diagnoses path issues, e.g., `traceroute google.com`.
329. What is the `mtr` command for troubleshooting?
Combines ping/traceroute, e.g., `mtr 8.8.8.8`.
330. What does the `netstat` command do for troubleshooting?
Shows connections, e.g., `netstat -anp`.
331. What is the `ss` command for troubleshooting?
Lists sockets, e.g., `ss -tuln`.
332. What does the `nmap` command do for troubleshooting?
Scans ports, e.g., `nmap 192.168.1.1`.
333. What is the `iperf` command for troubleshooting?
Tests bandwidth, e.g., `iperf -c server`.
334. What does the `ethtool` command do for troubleshooting?
Checks NIC, e.g., `ethtool eth0` for link status.
335. What is the `ip -s link` command for troubleshooting?
Shows errors, e.g., `ip -s link show eth0`.
336. What does the `nc` command do for troubleshooting?
Tests ports, e.g., `nc -zv localhost 80`.
337. What is the `telnet` command for troubleshooting?
Tests connectivity, e.g., `telnet localhost 22`.
338. What does the `dig` command do for troubleshooting?
Diagnoses DNS, e.g., `dig +trace example.com`.
339. What is the `nslookup` command for troubleshooting?
Tests DNS, e.g., `nslookup example.com`.
340. What does the `arp` command do for troubleshooting?
Checks ARP cache, e.g., `arp -n`.
341. What is the `ip neighbor` command for troubleshooting?
Diagnoses ARP, e.g., `ip neighbor show`.
342. What does the `route` command do for troubleshooting?
Checks routes, e.g., `route -n`.
343. What is the `ip route get` command for troubleshooting?
Tests routing, e.g., `ip route get 8.8.8.8`.
344. What does the `iftop` command do for troubleshooting?
Identifies bandwidth hogs, e.g., `iftop -i eth0`.
345. What is the `nethogs` command for troubleshooting?
Shows process bandwidth, e.g., `nethogs eth0`.
346. What does the `vnstat` command do for troubleshooting?
Tracks usage, e.g., `vnstat -i eth0`.
347. What is the `iptraf` command for troubleshooting?
348. What does the `bmon` command do for troubleshooting?
Diagnoses bandwidth, e.g., `bmon`.
349. What is the `nload` command for troubleshooting?
Shows real-time usage, e.g., `nload eth0`.
350. What does the `hping3` command do for troubleshooting?
Tests connectivity, e.g., `hping3 -c 10 -S host`.
351. What is the `arping` command for troubleshooting?
Tests ARP, e.g., `arping 192.168.1.1`.
352. What does the `ethtool -S` command do for troubleshooting?
Shows packet errors, e.g., `ethtool -S eth0`.
353. What is the `ip monitor` command for troubleshooting?
Tracks changes, e.g., `ip monitor all`.
354. What does the `conntrack` command do for troubleshooting?
Shows NAT issues, e.g., `conntrack -L`.
355. What is the `tc` command for troubleshooting?
Diagnoses QoS, e.g., `tc -s qdisc show dev eth0`.
356. What does the `ipset` command do for troubleshooting?
Checks IP sets, e.g., `ipset list`.
357. What is the `nft list` command for troubleshooting?
Shows firewall rules, e.g., `nft list ruleset`.
358. What does the `firewall-cmd` command do for troubleshooting?
Checks firewall, e.g., `firewall-cmd --list-all`.
359. What is the `iptables -L` command for troubleshooting?
Lists rules, e.g., `iptables -L -v`.
360. What does the `ufw status` command do?
Shows firewall status, e.g., `ufw status`.
361. What is the `netstat -s` command for troubleshooting?
Shows stats, e.g., `netstat -s` for packet errors.
362. What does the `ss -s` command do for troubleshooting?
Shows socket stats, e.g., `ss -s`.
363. What is the `lsof -i` command for troubleshooting?
Lists open ports, e.g., `lsof -i :80`.
364. What does the `fuser` command do for troubleshooting?
Identifies processes, e.g., `fuser 80/tcp`.
365. What is the `ip link` command for troubleshooting?
Checks interface, e.g., `ip link show eth0`.
366. What does the `ethtool -t` command do?
Tests NIC, e.g., `ethtool -t eth0`.
367. What is the `iw dev` command for troubleshooting?
Checks Wi-Fi, e.g., `iw dev wlan0 link`.
368. What does the `rfkill list` command do?
Checks wireless blocks, e.g., `rfkill list`.
369. What is the `nmcli` command for troubleshooting?
Checks connections, e.g., `nmcli con show`.
370. What does the `ping -s` command do?
Tests MTU, e.g., `ping -s 1472 8.8.8.8`.
371. What is the `tracepath` command?
Similar to traceroute, e.g., `tracepath google.com`.
372. What does the `ip route cache` do?
Shows cached routes, e.g., `ip route show cache`.
373. What is the `ip neighbor flush` command?
Clears ARP cache, e.g., `ip neighbor flush dev eth0`.
374. What does the `tcpdump -vv` command do?
Verbose capture, e.g., `tcpdump -vv -i eth0`.
375. What is the `iperf -u` command?
Tests UDP, e.g., `iperf -u -c server`.
376. What does the `ethtool -g` command do?
Shows ring buffer, e.g., `ethtool -g eth0`.
377. What is the `ip mroute` command?
Shows multicast routes, e.g., `ip mroute show`.
378. What does the `socat` command do for troubleshooting?
Tests connections, e.g., `socat - TCP:localhost:80`.
379. What is the `bwm-ng` command for troubleshooting?
380. What does the `ipcalc` command do for troubleshooting?
Verifies subnets, e.g., `ipcalc 192.168.1.0/24`.
381. What is the `ip link stats` command?
Shows interface errors, e.g., `ip -s link show eth0`.
382. What does the `ethtool -i` command do?
Shows driver info, e.g., `ethtool -i eth0`.
383. What is the `ip addr flush` command?
Clears IPs, e.g., `ip addr flush dev eth0`.
384. What does the `ip link set promisc` command do?
Enables promiscuous mode, e.g., `ip link set eth0 promisc on`.
385. // Advanced Topics and Cloud Networking: What is SDN?
Software-Defined Networking, e.g., separates control, data planes.
386. What is OpenFlow?
SDN protocol, e.g., controls switches via controller.
387. What is a VPC?
Virtual Private Cloud, e.g., isolated cloud network in AWS.
388. What is a subnet in a VPC?
IP range in VPC, e.g., 10.0.1.0/24.
389. What is a route table in a VPC?
Controls VPC traffic, e.g., routes to internet gateway.
390. What is an internet gateway in a VPC?
Connects VPC to internet, e.g., enables public IPs.
391. What is a NAT gateway?
Allows outbound internet, e.g., for private subnets.
392. What is a security group in a VPC?
Instance-level firewall, e.g., allows port 80.
393. What is a network ACL in a VPC?
Subnet-level firewall, e.g., stateless rules.
394. What is a VPC peering?
Connects VPCs, e.g., routes traffic between two VPCs.
395. What is a transit gateway?
Hub for VPCs, e.g., simplifies multi-VPC routing.
396. What is a load balancer?
Distributes traffic, e.g., ELB in AWS.
397. What is an Application Load Balancer (ALB)?
Layer 7 balancer, e.g., routes based on HTTP headers.
398. What is a Network Load Balancer (NLB)?
Layer 4 balancer, e.g., handles TCP/UDP.
399. What is a Classic Load Balancer?
Older AWS balancer, e.g., supports layer 4/7.
400. What is a health check in load balancing?
Verifies instance status, e.g., HTTP 200 on port 80.
401. What is a CDN?
Content Delivery Network, e.g., CloudFront caches content.
402. What is an edge location?
CDN cache site, e.g., CloudFront’s global servers.
403. What is a reverse proxy in cloud?
Handles client requests, e.g., Nginx for load balancing.
404. What is a container network?
Isolates containers, e.g., Docker bridge network.
405. What is a CNI?
Container Network Interface, e.g., Calico, Flannel.
406. What is Calico?
Networking for containers, e.g., supports BGP, policies.
407. What is Flannel?
Overlay network, e.g., VXLAN for Kubernetes.
408. What is Weave?
Container networking, e.g., overlay with encryption.
409. What is a service mesh?
Manages microservices, e.g., Istio for traffic control.
410. What is Istio?
Service mesh, e.g., handles routing, observability.
411. What is Envoy?
Proxy for service mesh, e.g., used in Istio.
412. What is a sidecar proxy?
Per-pod proxy, e.g., Envoy in Istio.
413. What is VXLAN?
Virtual Extensible LAN, e.g., overlays layer 2 over layer 3.
414. What is a GRE tunnel in cloud?
Encapsulates packets, e.g., connects VPCs.
415. What is a VRF?
Virtual Routing and Forwarding, e.g., isolates routing tables.
416. What is a network overlay?
Virtual network, e.g., VXLAN over physical network.
417. What is a network underlay?
Physical network, e.g., supports overlays.
418. What is SR-IOV?
Single Root I/O Virtualization, e.g., high-performance NIC.
419. What is DPDK?
Data Plane Development Kit, e.g., accelerates packet processing.
420. What is a virtual switch?
Software switch, e.g., Open vSwitch for VMs.
421. What is Open vSwitch (OVS)?
Virtual switch, e.g., supports SDN, VLANs.
422. What is a flow table in OVS?
Rules for packet forwarding, e.g., OpenFlow-based.
423. What is a network namespace?
Isolates network stack, e.g., `ip netns add myns`.
424. What is a veth pair?
Virtual Ethernet, e.g., connects namespaces.
425. What is a bridge network?
Connects interfaces, e.g., `brctl addbr br0`.
426. What is a tap interface?
Layer 2 virtual interface, e.g., for VMs.
427. What is a tun interface?
Layer 3 virtual interface, e.g., for VPNs.
428. What is eBPF?
Extended Berkeley Packet Filter, e.g., programmable networking.
429. What is XDP?
eXpress Data Path, e.g., eBPF for packet processing.
430. What is a network policy?
Controls pod traffic, e.g., Kubernetes Calico rules.
431. What is a cloud router?
Manages cloud routes, e.g., Google Cloud Router.
432. What is a direct connect?
Dedicated cloud link, e.g., AWS Direct Connect.
433. What is a VPN gateway in cloud?
Terminates VPN, e.g., AWS VPN Gateway.
434. What is a peering connection?
Links cloud networks, e.g., VPC peering.
435. What is a global load balancer?
Distributes across regions, e.g., GCP HTTP Load Balancer.
436. What is DNS load balancing?
Routes via DNS, e.g., multiple A records.
437. What is anycast routing?
Routes to nearest node, e.g., Cloudflare DNS.
438. What is a WAF in cloud?
Protects apps, e.g., AWS WAF for SQL injection.
439. What is a DDoS protection service?
Mitigates attacks, e.g., AWS Shield.
440. What is a network function virtualization (NFV)?
Virtualizes network services, e.g., virtual firewalls.
441. What is a virtual appliance?
Preconfigured VM, e.g., Cisco vRouter.
442. What is a cloud-native network?
Designed for cloud, e.g., Kubernetes CNI.
443. What is a hybrid cloud network?
Connects on-prem, cloud, e.g., via VPN or Direct Connect.
444. What is a multi-cloud network?
Spans providers, e.g., AWS and Azure via peering.
445. What is a network telemetry?
Collects metrics, e.g., packet loss, latency.
446. What is gRPC?
High-performance RPC, e.g., used in microservices.
447. What is QUIC?
UDP-based protocol, e.g., improves HTTP/3 performance.
448. What is HTTP/3?
HTTP over QUIC, e.g., faster, more reliable.
449. What is a zero trust network?
Verifies all access, e.g., no implicit trust.
450. What is SASE?
Secure Access Service Edge, e.g., combines SD-WAN, security.
451. What is SD-WAN?
Software-Defined WAN, e.g., optimizes branch connectivity.
452. What is a network orchestration?
Automates configs, e.g., Ansible for routers.
453. What is a network automation?
Scripted tasks, e.g., Python for switch configs.
454. What is NetDevOps?
DevOps for networking, e.g., CI/CD for configs.
455. What is a network observability?
Monitors, analyzes, e.g., Prometheus, Grafana.
456. What is a packet broker?
Distributes packets, e.g., to monitoring tools.
457. What is a network tap in cloud?
Captures cloud traffic, e.g., AWS VPC Traffic Mirroring.
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