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Network Design and Operations

Learn with multiple-choice questions: MAC address learning, VLANs and trunks, STP and RSTP, link aggregation, VLSM and route summarization, longest prefix match, static routes and administrative distance, OSPF cost and BGP, inter-VLAN routing and VRRP, DHCP relay and DNS, port forwarding and ACLs, SLAAC and EUI-64, traceroute, fragmentation and path MTU discovery, QoS, SNMP and NetFlow, and troubleshooting.

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Network Design and Operations: key points

New to this topic? Start with: How Is Data Sent Over the Internet? Packets and Routers / What Is an IP Address? IPv4, IPv6 and Private IPs Explained

Company and data center networks connect switches and routers redundantly, divide them with VLANs, choose the best of several paths, and are designed so that communication continues when something fails. On top of that, services such as DHCP, DNS, NAT and ACLs are combined, and the network is operated while traffic and faults are monitored.

As the next step after "Computer Networking Basics," this topic covers MAC address learning in L2 switches, IEEE 802.1Q tags, trunk ports and inter-VLAN routing, loop prevention with STP and RSTP, link aggregation, VLSM and route summarization calculations, longest prefix match, static routes and administrative distance, distance-vector and link-state protocols, OSPF cost calculations, BGP and ASes, and VRRP. It goes on, with calculation and tracing questions, to DHCP relay, recursive DNS queries and TTL, port forwarding, the order in which ACLs are evaluated, IPv6 SLAAC and EUI-64, tunneling, traceroute, IPv4 fragmentation, path MTU discovery, QoS and queuing, SNMP, syslog and NetFlow, and troubleshooting layer by layer. It also helps as an introduction to the network sections of IT certification exams such as Japan's Applied Information Technology Engineer and Network Specialist Examinations.

All Network Design and Operations questions (40)
  1. When an L2 switch receives a frame, which information does it record in its MAC address table?
  2. An L2 switch with an empty MAC address table has devices on ports 1 to 4, all in the same VLAN. PC-A on port 1 sends a frame to PC-B on port 2, and PC-B then sends a reply frame to PC-A. How are the two frames forwarded?
  3. An L2 switch with four PCs is connected to one interface of a router. A repeater hub with three PCs is connected to the router's other interface. No VLANs are used. Counting a collision domain as the range in which frames can collide on half-duplex Ethernet, which is the correct pair of numbers of broadcast domains and collision domains?
  4. The VLAN ID in an IEEE 802.1Q tag is 12 bits long, and the values 0 and 4095 are reserved for special purposes. How many VLAN IDs can be used to identify VLANs?
  5. Switches SW1 and SW2 both have ports in VLAN 10 and VLAN 20. The two switches are to be connected with a single cable so that devices in the same VLAN can communicate across the switches. Which configuration of the connecting ports is appropriate?
  6. In a network where switches are connected with redundant paths, what role does the Spanning Tree Protocol (STP) play?
  7. In STP, the bridge IDs of three switches are known: SW1 has priority 32768 and MAC address 00-00-5E-00-53-01, SW2 has priority 61440 and MAC address 00-00-5E-00-53-05, and SW3 has priority 4096 and MAC address 00-00-5E-00-53-0A. Which switch is elected as the root bridge?
  8. Three switches, SW1, SW2 and SW3, are connected in a triangle with one link between each pair. The STP root bridge is SW1, and SW2 has a lower bridge ID than SW3. All links have the same path cost. Which port is blocked (does not forward frames)?
  9. With default timers, classic STP (IEEE 802.1D) takes about 30 to 50 seconds after a failure before a previously blocked port starts forwarding. Which mechanism lets RSTP switch over faster?
  10. Four 1 Gbps links between two switches are bundled into one logical link with link aggregation. Frames are distributed with the common method that chooses the link for each combination of source and destination addresses and port numbers (each flow). Which is closest to the maximum throughput a single TCP connection can achieve?
  11. A router is to be connected with a single link to an L2 switch that has VLAN 10 (192.168.10.0/24) and VLAN 20 (192.168.20.0/24), so that the two VLANs can communicate with each other. Which configuration is appropriate for this setup?
  12. Two routers, R1 (192.168.1.2) and R2 (192.168.1.3), are configured with VRRP using the virtual IP address 192.168.1.254. Normally R1 forwards traffic as the master. Which address should be set as the default gateway on the LAN hosts?
  13. 192.168.10.0/24 is to be split into subnets for site A (100 hosts), site B (50 hosts) and site C (25 hosts). Starting with the site that needs the most hosts, each site is given the smallest subnet that holds its hosts, packed in from the lowest addresses. Which subnet is assigned to site C?
  14. Each of the following three sets consists of four consecutive /24 networks. For which set can the four routes be summarized into exactly one /22 route without including any addresses outside the set?
  15. A router's routing table has four routes: 172.16.0.0/12 (next hop router B), 172.16.32.0/19 (router A), 172.16.48.0/20 (router C) and 0.0.0.0/0 (router D). To which router is a packet for 172.16.45.10 sent?
  16. Branch router R2 is connected to head-office router R1 over a 10.255.0.0/30 link, with R1's end at 10.255.0.1 and R2's at 10.255.0.2. When a static route to the head-office network 192.168.1.0/24 is configured on R2, which address is appropriate as the next hop?
  17. A router has learned routes to the same destination, 192.168.50.0/24, from both OSPF and RIP. On this router, the administrative distance, which expresses the preference for each route source (lower is preferred), is 110 for OSPF and 120 for RIP. Which route goes into the routing table?
  18. A router's routing table holds three routes: a static route 10.0.0.0/8 (next hop router A, administrative distance 1), 10.1.0.0/16 learned by OSPF (router B, 110) and 10.1.1.0/24 learned by RIP (router C, 120). To which router is a packet for 10.1.1.5 sent?
  19. Which statement correctly describes a link-state routing protocol?
  20. In OSPF, router R1 has three paths to a network beyond R4. Path A uses a 10 Gbps link R1–R5 and a 1 Gbps link R5–R4; path B is a direct 100 Mbps link R1–R4; and path C uses 1 Gbps links R1–R2, R2–R3 and R3–R4. The cost of each link is "reference bandwidth 10 Gbps ÷ link bandwidth", and the cost beyond R4 is the same for all paths. Which path does R1 choose?
  21. On the internet, which protocol exchanges routing information between the networks run by organizations such as ISPs (ASes, autonomous systems) and chooses routes based on attributes such as the sequence of ASes a route has passed through (AS_PATH) and on each organization's policy?
  22. Hosts in VLAN 20 (192.168.20.0/24) are to get addresses from a DHCP server, 10.0.0.5, on another network. A DHCP relay agent is therefore configured on the L3 switch interface 192.168.20.1, which is VLAN 20's default gateway. Which statement correctly describes what the relay agent does?
  23. Which DNS resource record specifies the mail server that receives email addressed to a domain?
  24. Which statement correctly describes how recursive and non-recursive (iterative) queries are used in DNS name resolution?
  25. For a web server move, the IP address in the A record for www.example.com will be changed. The record's TTL is currently 86400 seconds, and to keep the time the old address is used after the change to about 5 minutes at most, the TTL will be lowered to 300 seconds beforehand. Resolvers cache records exactly for their TTL. Which is the correct deadline for lowering the TTL?
  26. A router that performs NAPT (outside address 198.51.100.7) is configured with port forwarding, a static setting that translates only the destination: "forward traffic arriving at outside TCP port 8080 to port 80 on the inside web server 192.168.1.20." When host 203.0.113.9 on the internet connects from source port 51000 to port 8080 on 198.51.100.7, which is the destination and source of the packets the web server receives?
  27. An ACL that checks incoming packets from the top is applied to a router interface. Rule 1 is "permit traffic to TCP port 443 on 10.0.0.10," rule 2 is "deny all traffic from source 192.168.1.0/24," and rule 3 is "permit traffic from source 192.168.0.0/16 to TCP port 80"; there are no other rules. Of the four packets (i) "from 192.168.1.5 to TCP port 443 on 10.0.0.10," (ii) "from 192.168.1.5 to TCP port 80 on 10.0.0.20," (iii) "from 192.168.2.5 to TCP port 80 on 10.0.0.20" and (iv) "from 192.168.2.5 to TCP port 22 on 10.0.0.20," which choice lists all the packets that are let through?
  28. In IPv6, which range holds link-local addresses, which are used only within the same link and are always configured automatically on every interface that uses IPv6?
  29. In IPv6 SLAAC (stateless address autoconfiguration), how does a host create a global unicast address?
  30. An interface with MAC address 00-1A-2B-3C-4D-5E creates an address with SLAAC from the prefix 2001:db8:1:1::/64 and an interface ID in the EUI-64 format. Which address results?
  31. Two sites that run only IPv6 are to be connected through a network that runs only IPv4, and the traffic between the sites should remain IPv6 packets. Which method is appropriate?
  32. In traceroute, what value is the TTL in the IP header set to in the packet sent to make the fourth router from the source return an ICMP Time Exceeded message?
  33. Running traceroute from a host to web server 198.51.100.80 showed, on lines 1 to 5, 192.168.1.1, 10.0.0.1, "* * *" (no response), 203.0.113.1 and 198.51.100.80, in that order, and the web server could be used without problems. Which is the most appropriate interpretation of line 3?
  34. In IPv4, a packet with a total length of 4000 bytes (a 20-byte header and 3980 bytes of data) is split up (fragmented) on a link with an MTU of 1500 bytes. The fragments also have 20-byte headers, and fragmentation is allowed. What is the value of the fragment offset field in the last fragment?
  35. A host communicates with a distant web server through a site-to-site VPN tunnel. TCP connections can be established and small pages load, but large file downloads stall partway. The MTU inside the tunnel is 1400 bytes, and the server sends 1500-byte packets with fragmentation prohibited (the DF bit set to 1). The firewall in front of the server is also set to discard all ICMP. Which is the most likely cause?
  36. Which statement correctly describes DSCP in the IP header, used in QoS control?
  37. On a 70 Mbps outgoing link of a router, three queues are served by weighted round robin with weights 4:2:1. All three queues always have packets waiting, and all packets are the same size. Which is closest to the bandwidth available to the queue with weight 2?
  38. Using SNMP, a router interface's 64-bit counter of received bytes is read every 5 minutes (300 seconds). The previous reading was 1,200,000,000 and the current one is 4,950,000,000. Which is closest to the average receive rate over these 5 minutes?
  39. For the traffic passing through a router, you want to find out how many bytes are taken up by each combination of source and destination (addresses, port numbers and protocol), aggregated per stream of traffic. Which mechanism is the most appropriate to use?
  40. From a PC, ping with an IP address reaches a server on the internet, but when a domain name is entered in the browser it shows "server not found" and the web page does not open. Which setting is the most appropriate to check first?

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