15 D. When an interface is configured as a passive interface, OSPF will advertise the prefix for that interface, but will not form an adjacency with other routers on the subnet. See Chapter 5 for more information.
16 C. The route is an external Enhanced Interior Gateway Routing Protocol (EIGRP) route, so it has an administrative distance of 170. See Chapter 6 for more information.
17 A, B. By default, only bandwidth and delay are used in calculating the metric. See Chapter 6 for more information.
18 B. 10.0.56.6 is the feasible successor. See Chapter 6 for more information.
19 C. Border Gateway Protocol (BGP) uses the autonomous system (AS) path for loop prevention. Upon receiving a route with its own AS in the AS path, an exterior Border Gateway Protocol (eBGP) router will discard the route, meaning it won't install it in its BGP Routing Information Base (RIB) or IP routing table, nor will it advertise the route. See Chapter 7 for more information.
20 A. 172.16.0.0/24 doesn't exist in R1's routing table, so the network command will have no effect. Instead, the redistribute eigrp 16 command will redistribute the 172.16.0.0/16 prefix into BGP with an incomplete origin type. See Chapter 7 for more information.
21 C. The prefix list matches any prefix with a subnet falling into the 10.0.0.0/8 range with a prefix length from 8 to 32. This includes 10.0.0.0/8, 10.0.0.0/32, and 10.255.255.0/24. The first sequence in the route map is a deny sequence that matches the IP prefix list. Hence, these prefixes will match the sequence and will be denied. The second sequence in the route map is a permit sequence that matches all prefixes that don't match the first sequence. See Chapter 7 for more information.
22 A. R2 is translating the source address 7.0.0.12 to 2.0.0.2; therefore 7.0.0.12 is the inside local address and 2.0.0.2 is the inside global address. See Chapter 8 for more information.
23 C. Multicast RIB entries take the form (source, group). The entry indicates that the source—223.3.2.1—has sent multicast traffic to the multicast group address 239.8.7.6. See Chapter 8 for more information.
24 D. Port address translation—also known as network address translation (NAT) overload—translates multiple inside local source addresses to a single global address. The global address can come from an outside interface or from a pool. See Chapter 8 for more information.
25 B. CS1 gets a lower priority than CS0. CS0 is the default class and is for best-effort traffic. CS1 is the bottom-of-the-barrel traffic that you may not even want on your network, such as torrents, gaming, or cat videos. See Chapter 9 for more information.
26 A, C. TCP global synchronization occurs when multiple TCP flows back off, then ramp up simultaneously. This can happen when a queue fills and excess packets are tail-dropped. Weighted random early detection (WRED) randomly drops packets as the queue fills. Explicit congestion notification (ECN) works by getting a TCP sender to slow down the rate at which it sends by reducing its congestion window. See Chapter 9 for more information.
27 A. The low-latency queuing (LLQ) is serviced before any other queues, so packets in the LLQ won't wait any longer than necessary. The LLQ has a limited bandwidth. See Chapter 9 for more information.
28 D. The term edge virtual bridging (EVB) describes using a physical switch to pass layer 2 traffic between VMs running on the same host. The IEEE 802.1Qbg standard calls this reflective relay. See Chapter 10 for more information.
29 B, C. Internet Key Exchange (IKE) uses User Datagram Protocol (UDP) port 500, whereas Encapsulating Security Payload (ESP) uses IP protocol 50. See Chapter 10 for more information.
30 A, C. By default, Virtual Extensible LAN (VXLAN) uses multicast to flood unknown unicasts, allowing it to perform data plane learning. See Chapter 10 for more information.
31 C. SD-Access uses VXLAN encapsulation because it can carry Ethernet frames. The others can't. See Chapter 11 for more information.
32 B. Software-defined networking in a wide area network (SD-WAN) doesn't use BGP. See Chapter 11 for more information.
33 A. When authenticating using a GET or PUT request, you should get a 200 response code if authentication succeeds. See Chapter 11 for more information.
34 A. Terminal Access Controller Access-Control System Plus (TACACS+) supports authorization, authentication, and accounting. Remote Authentication Dial-In User Service (RADIUS) doesn't support command authorization. See Chapter 12 for more information.
35 C. MAC authentication bypass is the only option that can authenticate a machine but not a user. See Chapter 12 for more information.
36 A, D. You can't use a port access control list (ACL) to block certain control plane traffic, including ARP and Spanning Tree BPDUs. You also can't use an extended IP ACL because ARP and Spanning Tree Protocol (STP) don't use IP. See Chapter 12 for more information.
Chapter 1 Networking Fundamentals
THE CCNP ENCOR EXAM OBJECTIVES COVERED IN THIS CHAPTER INCLUDE THE FOLLOWING:
Domain 1.0: Architecture✓ 1.1 Explain the different design principles used in an enterprise network✓ 1.7 Differentiate hardware and software switching mechanisms
Domain 3.0: Infrastructure✓ 3.1 Layer 2✓ 3.2 Layer 3
Networking fundamentals can at times seem abstract and even impractical. It's important to remember that networks are both logical and physical, so you need to keep a tight grip on both. If you neglect theory and just focus on typing in commands, you'll end up with a jalopy network. It might work, but not very well, and probably not for long. On the other hand, learning theory that you fail to put into practice leads to being educated but unemployed.
This chapter will give you a solid theoretical foundation on which to build practical skills. Much of the theory should already be familiar to you, and you'll likely have some “I already know this stuff” moments. But more often than not you'll gain new insights on something you already understood.
There's a lot of networking information out there, much of which is poorly explained, if not just plain wrong. Networking myths abound on forums, blogs, and even Wikipedia. Even official Cisco documentation has been known to contain the occasional errata. It's not intentional, of course. Learning networking is no different than learning any other complex topic. Some concepts are easy, whereas others just never quite click. Those harder concepts are fertile breeding ground for misconceptions that eventually get passed around until they become common knowledge, or worse, “best practices.” Almost every network professional I've encountered holds at least one glaring misconception about networking that eventually ends up stumping them (sometimes on an exam!). Chances are you, too, have been the unfortunate recipient of such information. The sooner we identify and dispel those myths, the better. That's what this chapter is all about.
The OSI Model
The origin of many networking myths can be traced back to the Open Systems Interconnection (OSI) reference model developed by Charles Bachman of Honeywell and formalized by the International Organization for Standardization (ISO). The ISO intended the OSI model to be a standard framework for data networks. It describes a set of “activities necessary for systems to interwork using communication media” (ISO/IEC 7498-4). The model organizes these activities or functions into the following seven layers:
7. Application
6.