OSI MASTERY

Unplugged Ethernet cable - which layer

Physical

Damaged fiber optic cable - which layer

Physical

Wi-Fi signal too weak to connect - which layer

Physical

Wrong cable type causing no link light - which layer

Physical

Switch has a bad port - which layer

Physical

Duplicate MAC address on the network - which layer

Data Link

VLAN misconfiguration - which layer

Data Link

Switch MAC address table is full - which layer

Data Link

Frame fails its checksum and is dropped - which layer

Data Link

Duplicate IP address conflict - which layer

Network

Wrong default gateway configured - which layer

Network

Wrong subnet mask blocking communication - which layer

Network

Missing route in the routing table - which layer

Network

Ping fails with destination unreachable - which layer

Network

Packet dropped because TTL hit zero - which layer

Network

Firewall blocking port 443 - which layer

Transport

Web server not listening on the expected port - which layer

Transport

Retransmissions due to packet loss - which layer

Transport

Two apps on one server distinguished by port number - which layer

Transport

Expired SSL certificate warning in browser - which layer

Presentation

Data encrypted before transmission - which layer

Presentation

Image encoded as JPEG for transfer - which layer

Presentation

Website returns 404 error - which layer

Application

DNS server not responding - which layer

Application

Wrong URL typed in browser - which layer

Application

Email fails because SMTP server rejects it - which layer

Application

User can ping IP but not the domain name - what service is broken

DNS

You can ping 8.8.8.8 but google.com fails - what service is broken

DNS

Laptop gets no IP address when joining network - what service failed

DHCP

PC knows the gateway IP but not its MAC - what protocol runs

ARP

traceroute works by manipulating what field

TTL

ping uses what protocol

ICMP

Transport protocol used when loss is acceptable but speed matters

UDP

Transport protocol used when data must arrive complete and in order

TCP

Transport protocol typically used for streaming video

UDP

Transport protocol typically used for online gaming and voice calls

UDP

Transport protocol used for file downloads

TCP

Transport protocol used when loading a bank website

TCP

Transport protocol used for email delivery

TCP

Why does a switch flood a frame to all ports

Unknown destination MAC

Feature that lets many home devices share one public IP

NAT

Which two layers does a Wi-Fi access point mainly work at

Physical and Data Link

Which two layers does ARP glue together

Data Link and Network

Which two values does a NAT translation table track

IP address and port

Which two layers do MAC and IP addressing belong to

Data Link and Network

A layer 3 switch operates at which two layers

Data Link and Network

HTTPS combines HTTP and TLS - which two layers

Application and Presentation

Cable tester checks which layer

Physical

Wireshark showing TCP retransmissions - which layer are you analyzing

Transport

ipconfig or ip addr shows info for which layer

Network

arp -a displays a table mapping which two address types

IP and MAC

netstat or ss showing listening ports - which layer

Transport

nslookup or dig troubleshoots which service

DNS

Only one specific website fails for a user - likely layer

Application

Everyone on one switch loses connectivity - start troubleshooting at which layer

Physical