Models and how networks work
Topic 1 of 26. 46 questions: 22 pick one, 5 pick all, 7 type it, 4 put in order, 8 interview
What this topic covers
- OSI model layer by layer and what lives at each layer
- TCP/IP model and how it maps to OSI
- encapsulation and PDU names
- what happens end to end when you open a website
- hub vs switch vs router vs firewall
- collision vs broadcast domains
- unicast multicast broadcast anycast
- bandwidth vs throughput vs latency vs jitter
- LAN WAN MAN PAN WLAN
- topologies star mesh ring
- ARP basics
- MAC vs IP addressing roles
- client server vs peer to peer
- control plane data plane management plane
Study it in depth on Octet.
- 1Put the seven OSI layers in order, from layer 1 at the bottom to layer 7 at the top.
- 2Walk me through the OSI model layer by layer, with an example of what lives at each layer.
- 3Which OSI layer uses port numbers to deliver data to the right process on a host?
- 4Which of these are handled at layer 2 of the OSI model? Choose all that apply.
- 5In the four-layer TCP/IP model, which OSI layers does the TCP/IP application layer cover?
- 6Put these PDU names in the order the data takes them as it moves down the stack on the sender, from the application to the wire.
- 7A host sends a full-size TCP segment on an Ethernet link with a 1500-byte MTU. The IPv4 and TCP headers carry no options. How many bytes of application data fit in that packet?
- 8PC1 opens a connection to a web server on the internet, and this capture is taken on PC1's own interface. Which device owns the destination MAC address 00:1a:2b:3c:4d:5e?
- 9A router forwards an IPv4 packet from one Ethernet segment to another. There is no NAT. Which of these does the router change? Choose all that apply.
- 10PC1 (10.1.1.10) receives this frame. Which fields does its network stack use to decide which protocol, and finally which program, gets the payload next? Choose all that apply.
- 11BGP is a routing protocol, so people often file it under layer 3. How is a BGP message actually carried?
- 12Which value in the IPv4 Protocol field tells the receiver that the payload is UDP?
- 13Is the OSI model how real networks work? Give me examples of where it breaks down.
- 14What is the difference between a hub, a switch, a router and a firewall?
- 15A firewall is inserted in transparent (layer 2) mode between a subnet's hosts and their default gateway router. What changes for the hosts on that subnet?
- 16SW1 receives a frame in VLAN 10 on Gi0/3 with destination MAC 0050.56a1.0b20. What does it do with the frame?
- 17What does a stateful firewall do that a router with a stateless ACL does not?
- 18Two stateful firewalls, FW1 and FW2, sit on parallel paths and do not share state. A client's SYN leaves through FW1, and the server's SYN-ACK comes back through FW2. What happens?
- 19A 24-port switch has a host on every port. The ports are split across VLANs 10, 20 and 30, and no other VLAN has ports. How many broadcast domains and collision domains are there?
- 20How many collision domains are in this network?
- 21Several servers in different cities share one IP address, and each packet goes to whichever server is nearest by routing. What is this delivery type called?
- 22Which statements about IPv4 multicast are true? Choose all that apply.
- 23Why is anycast a safer fit for DNS over UDP than for long-lived TCP sessions?
- 24PC1 has just booted, so its ARP cache is empty. The user runs ping 8.8.8.8. Which IP address does PC1 send an ARP request for?
- 25On an Ethernet LAN, how are an ARP request and its reply normally addressed at layer 2?
- 26Users report that 10.1.1.50 cannot be reached from other subnets. What does R1's entry for 10.1.1.50 tell you?
- 27Host A sends its first packet to host B on the same subnet and has never talked to it before. Put the steps in order, first to last.
- 28Why does a host need both a MAC address and an IP address?
- 29A VoIP call to 10.20.0.15 sounds choppy, yet this ping shows no loss. Which property of the path does the output point to?
- 30Explain the difference between bandwidth, throughput, latency and jitter.
- 31A WAN link between two offices 3,000 km apart is upgraded from 100 Mbps to 1 Gbps. Which part of the delay does the upgrade not reduce?
- 32How long does it take to serialize a 1500-byte frame onto a 1 Gbps link? Give the answer in microseconds.
- 33Light in fiber travels at about 200,000 km per second. What is the one-way propagation delay over a 2,000 km fiber path, in milliseconds?
- 34A path has 1 Gbps of bandwidth and an 80 ms round-trip time. What is its bandwidth-delay product in megabytes, taking 1 MB as 1,000,000 bytes?
- 35A single TCP flow uses a 65,535-byte receive window with no window scaling. The round-trip time is 100 ms and the link is 1 Gbps. What is the most this flow can reach?
- 36A Bluetooth headset paired with a phone forms which type of network?
- 37What most sets a WAN apart from a LAN in practice?
- 38How many point-to-point links does a full mesh of 8 sites need?
- 39A metro Ethernet ring connects six layer 2 switches, each to its two neighbors. What must run on the ring for it to work?
- 40Which of these are control plane functions on a network device? Choose all that apply.
- 41Explain the control, data and management planes, and why the separation matters.
- 42A router's CPU sits at 100% because of a flood of packets addressed to the router's own interfaces, while transit traffic is mostly unaffected. Which plane is under attack, and which Cisco IOS feature limits the damage?
- 43What is the difference between client-server and peer-to-peer, and can you give an example of each?
- 44Which of these is an example of peer-to-peer communication?
- 45What happens, end to end, when you type https://www.example.com into a browser and press Enter?
- 46A laptop already has its address from DHCP, but its ARP and DNS caches are empty and its DNS resolver is on another subnet. The user opens https://www.example.com, which is served over HTTP/2. Put these steps in order, first to last.