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8,710 network engineer interview questions shared by candidates

1. OSI Ref Model/TCP-IP Model · Explanation of each layer · Protocols at each layer 2. ARP · Packet structure ARP, GARP · Diff between ARP & GARP 3. Ethernet Frame · Fields in Ethernet II frame · Size of Ethernet Frame · LLC & MAC Sublayer 4. IP · Fields in IP header · Importance of Identification field, Flags, Fragment Offset · Fragmentation-Importance, Detailed understanding of how packet is reassembled · Path MTU Discovery 5. TCP · 3 way handshake · Parameters Informed, negotiated in TCP · Fields in TCP header · Windowing in TCP · Purpose of Sequence, Ack number · Window Size , MSS, Windows Scale Factor, SACK · Zero Window · Diff between MSS & MTU · Flags -SYN,ACK,FIN,RST,PSH,URG · Diff between Push & Urg , Purpose of RST bit · Segmentation · 4 way close · Flow Control –Sliding Window · Error Control – TCP retransmissions 6. FTP · How Active & Passive FTP works · PORT & PASV command · Troubleshooting FTP issues 7. Traceroute , ICMP, Ping · How Traceroute, Tracert works · ICMP message in traceroute · ICMP Type & Code (Type 8, Type 0, Type 3, Type 11) · Meaning of traceroute output 8. Switching & Routing Basics · Working of a Layer 2 switch · MAC Table, CAM Table , ARP Table · Static & Default Route 9. Firewall · Stateful vs stateless Firewall · Parameters in a Session Table · NAT , PAT · TCP Packet through Firewall , SYN check, Sequence check · FTP connection through Firewall, Troubleshooting · Deep Packet Inspection / ALG · Transparent Firewall · High Availability – Active/Standby , Active/Active , How Standby knows if Active is down · SYN Flood Attack & Mitigation · IP spoofing & Mitigation 10. VPN · Need for VPN · Types of VPN · Phase 1 & Phase 2 messages – Main mode, Aggressive Mode, Quick Mode · Need for 2 Phases in IPsec · Symmetric & Asymmetric keys, Hash & HMAC,DH group · Troubleshooting if various messages not received in IPsec (Msg1,Msg2,Msg3,Msg4,Msg5,Msg6) · Why Phase 1 is needed · Reasons why VPN Phase 1 does not come up · VPN Phase 1 up , Phase 2 down – Troubleshoot · VPN Phase 1 up , Phase 2 up , Traffic not flowing – Troubleshoot · Traffic Flowing but Latency Issue-Troubleshoot · Tunnel Mode & Transport Mode · Overlapping subnets · NAT-T(NAT Discovery) –VPN msgs for NAT-T Negotiation & Discovery · ESP,AH · Replay Attack & Mitigation · Ports to be allowed on Firewall for VPN
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Network Engineer

Interviewed at Movate

3.6★
Aug 24, 2016

1. OSI Ref Model/TCP-IP Model · Explanation of each layer · Protocols at each layer 2. ARP · Packet structure ARP, GARP · Diff between ARP & GARP 3. Ethernet Frame · Fields in Ethernet II frame · Size of Ethernet Frame · LLC & MAC Sublayer 4. IP · Fields in IP header · Importance of Identification field, Flags, Fragment Offset · Fragmentation-Importance, Detailed understanding of how packet is reassembled · Path MTU Discovery 5. TCP · 3 way handshake · Parameters Informed, negotiated in TCP · Fields in TCP header · Windowing in TCP · Purpose of Sequence, Ack number · Window Size , MSS, Windows Scale Factor, SACK · Zero Window · Diff between MSS & MTU · Flags -SYN,ACK,FIN,RST,PSH,URG · Diff between Push & Urg , Purpose of RST bit · Segmentation · 4 way close · Flow Control –Sliding Window · Error Control – TCP retransmissions 6. FTP · How Active & Passive FTP works · PORT & PASV command · Troubleshooting FTP issues 7. Traceroute , ICMP, Ping · How Traceroute, Tracert works · ICMP message in traceroute · ICMP Type & Code (Type 8, Type 0, Type 3, Type 11) · Meaning of traceroute output 8. Switching & Routing Basics · Working of a Layer 2 switch · MAC Table, CAM Table , ARP Table · Static & Default Route 9. Firewall · Stateful vs stateless Firewall · Parameters in a Session Table · NAT , PAT · TCP Packet through Firewall , SYN check, Sequence check · FTP connection through Firewall, Troubleshooting · Deep Packet Inspection / ALG · Transparent Firewall · High Availability – Active/Standby , Active/Active , How Standby knows if Active is down · SYN Flood Attack & Mitigation · IP spoofing & Mitigation 10. VPN · Need for VPN · Types of VPN · Phase 1 & Phase 2 messages – Main mode, Aggressive Mode, Quick Mode · Need for 2 Phases in IPsec · Symmetric & Asymmetric keys, Hash & HMAC,DH group · Troubleshooting if various messages not received in IPsec (Msg1,Msg2,Msg3,Msg4,Msg5,Msg6) · Why Phase 1 is needed · Reasons why VPN Phase 1 does not come up · VPN Phase 1 up , Phase 2 down – Troubleshoot · VPN Phase 1 up , Phase 2 up , Traffic not flowing – Troubleshoot · Traffic Flowing but Latency Issue-Troubleshoot · Tunnel Mode & Transport Mode · Overlapping subnets · NAT-T(NAT Discovery) –VPN msgs for NAT-T Negotiation & Discovery · ESP,AH · Replay Attack & Mitigation · Ports to be allowed on Firewall for VPN

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