Appendix C. Answers to the “Do I Know This Already?” Quizzes

Chapter 1

1. D and E. Many headers include a field that identifies the next header that follows inside a message. Ethernet uses the Ethernet Type field, and the IP header uses the Protocol field. The TCP and UDP headers identify the application that should receive the data that follows the TCP or UDP header by using the port number field in the TCP and UDP headers, respectively.

2. A, B, C, and F. IP, not TCP, defines routing. Many other protocols define encryption, but TCP does not. The correct answers simply list various TCP features.

3. C. TCP, not UDP, performs windowing, error recovery, and ordered data transfer. Neither performs routing or encryption.

4. C and F. The terms packet and L3PDU refer to the header plus data encapsulated by Layer 3. Frame and L2PDU refer to the header (and trailer), plus the data encapsulated by Layer 2. Segment and L4PDU refer to the header and data encapsulated by the transport layer protocol.

5. B. Note that the hostname is all the text between the // and the /. The text before the // identifies the application layer protocol, and the text after the / represents the name of the web page.

6. C and D. Web traffic uses TCP as the transport protocol, with HTTP as the application protocol. As a result, the web server typically uses well-known TCP port 80, which is the well-known port for HTTP traffic. Messages flowing to the web server would have a destination TCP port of 80, and messages flowing from the server would have a source TCP port of 80.

Chapter 2

1. A and C. Standard ACLs check the source IP address. The address range– can be matched by an ACL, but it requires multiple access-list commands. Matching all hosts in Barney’s subnet can be accomplished with the access-list 1 permit command.

2. A and D. The range of valid ACL numbers for standard numbered IP ACLs is 1–99 and 1300–1999, inclusive.

3. D. matches all packets that have the same first three octets. This is useful when you want to match a subnet in which the subnet part comprises the first three octets, as in this case.

4. E. matches all packets with the same first 20 bits. This is useful when you want to match a subnet in which the subnet part comprises the first 20 bits, as in this case.

5. A. The router always searches the ACL statements in order, and stops trying to match ACL statements after a statement is matched. In other words, it uses first-match logic. A packet with source IP address would match any of the three explicitly configured commands described in the question. As a result, the first statement will be used.

6. B. One wrong answer, with wildcard mask, matches all packets that begin with 172.16, with a 5 in the last octet. One wrong answer matches only specific IP address One wrong answer uses a wildcard mask of, which has only one wildcard bit (in binary), and happens to only match addresses and The correct answer matches the range of addresses–

Chapter 3

1. E and F. Extended ACLs can look at the Layer 3 (IP) and Layer 4 (TCP, UDP) headers and a few others, but not any application layer information. Named extended ACLs can look for the same fields as numbered extended ACLs.

2. A and E. The correct range of ACL numbers for extended IP access lists is 100 to 199 and 2000 to 2699. The answers that list the eq www parameter after match the source port number, and the packets are going toward the web server, not away from it.

3. E. Because the packet is going toward any web client, you need to check for the web server’s port number as a source port. The client IP address range is not specified in the question, but the servers are, so the source address beginning with 172.16.5 is the correct answer.

4. A and C. Before IOS 12.3, numbered ACLs must be removed and then reconfigured to remove a line from the ACL. As of IOS 12.3, you can also use ACL configuration mode and sequence numbers to delete one ACL line at a time.

5. C and D. In the command output, line number 10 references a permit command that matches addresses in subnet The question stem identifies the subnet, so it indirectly asks about line 10 of the ACL. Any specific Access Control Entry (ACE) in ACL can be deleted in ACL config mode. Two methods can be used: the short no line-number, where line-number is the ACE’s line number, or by issuing a no version of the permit or deny command, as shown in one of the correct answers. The three incorrect answers show correct commands but incorrect modes in which to use the commands.

6. C and D. The show ip access-lists and show access-lists commands both display the configuration of IPv4 access lists, including ACL line numbers. Neither the show running-config nor show startup-config commands list the ACL line numbers; in this case, the startup-config file would not contain the ACL configuration at all.

Chapter 4

1. B. A vulnerability is a weakness that can be exploited. Attack is not correct because it is a threat that is taking place.

2 D. When a vulnerability can be exploited, a threat is possible.

3. A and B. Attackers usually spoof the source IP address in packets they send in order to disguise themselves and make the actual IP address owner into a victim of the attack. MAC addresses can also be spoofed in ARP replies to confuse other hosts and routers on the local network. Destination IP addresses are not normally spoofed because packets used in the attack would go to unknown or nonexistent hosts. Finally, ARP address is not correct because it is not a legitimate term.

4. D. A denial-of-service attack is likely occurring because the attacker is trying to exhaust the target’s TCP connection table with embryonic or incomplete TCP connections.

5. C. In a reflection attack, the goal is to force one host (the reflector) to reflect the packets toward a victim. Therefore, the spoofed source address contains the address of the victim and not the reflector.

6. A and C. Once an attacker is in position in a man-in-the-middle attack, traffic between hosts can be passively inspected and actively modified. This type of attack does not lend itself to inducing buffer overflows or using sweeps and scans.

7. B. In a brute-force attack, an attacker’s software tries every combination of letters, numbers, and special characters to eventually find a string that matches a user’s password.

8. D. The Cisco ISE platform provides the AAA services needed for authentication, authorization, and accounting. DHCP does not perform AAA but leases IP addresses to hosts instead. DNS resolves hostnames to IP addresses. SNMP is used for network management functions.

9. C. Physical access control is a necessary element of a security program that keeps sensitive locations like data centers and network closets locked and inaccessible, except to authorized personnel.

Chapter 5

1. B. If both commands are configured, IOS accepts only the password as configured in the enable secret command

2. A. The service password-encryption command encrypts passwords on a router or switch that would otherwise be shown in clear text. While a great idea in concept, the algorithm can be easily broken using websites found in the Internet. Cisco long ago provided replacements for commands that store passwords as clear text, instead using hashes—commands like enable secret and username secret. These commands are preferred in part because they avoid the issues of clear-text passwords and easily decrypted passwords.

3. B. The enable secret command stores an MD5 hash of the password. It is unaffected by the service password-encryption command. The router does not unhash the value back to the clear-text password. Instead, when the user types her clear-text password, the router also hashes that password and compares that hashed value with the hashed value as listed in the configuration.

4. A. The ip access-class 1 in command enables ACL 1 for processing inbound Telnet and SSH connections into that router, based on the source IP address of those incoming packets. It has no impact on Telnet or SSH attempts from the router to some other host. It has no impact on a user later reaching enable mode. It also has nothing to do with filtering packets that would otherwise be routed through the router. Note that the ACL matches all packets whose source IP address is in subnet, which includes the range of numbers from to

5. B. Traditional and next-generation firewalls can check TCP and UDP port numbers, but next-generation firewalls are generally characterized as being able to also check application data beyond the Transport layer header. An NGFW would look into the application data, identifying messages that contain data structures used by Telnet, instead of matching with port numbers. This matching can catch attacks that seek to use port numbers that the firewall allows while using those ports to send data from applications that do not normally use those ports.

For the other answers, a traditional firewall would likely match based on destination port 23, which is the well-known port for Telnet. IP protocol number has nothing to do with Telnet.

6. A and D. Both traditional and next-generation IPSs (NGIPSs) use a signature database, with each signature listing details of what fields would be in a series of messages to identify those messages as part of some exploit. They both also generate events for review by the security team.

NGIPS devices add features that go beyond using a signature database, including gathering contextual information from hosts, like the OS used, currently running apps, open ports, and so on, so that the NGIPS does not have to log events if the hosts could not possibly be affected. Additionally, an NGIPS can use a list of reputation scores about IP addresses, domain names, and URIs of known bad actors, filtering traffic for sources that have a configured poor reputation level.

Chapter 6

1. B. The setting for the maximum number of MAC addresses has a default of 1, so the switchport port-security maximum command does not have to be configured. With sticky learning, you do not need to predefine the specific MAC addresses either. However, you must enable port security, which requires the switchport port-security interface subcommand.

2. B and D. First, about the sticky parameter…this command causes the switch to learn the source MAC and to add it to a switchport port-security mac-address address interface subcommand. However, port security adds that command to the running-config file; the network engineer must also issue a copy running-config startup-config EXEC command to save that configuration.

About the other correct answer, users can connect a switch to the end of the cable, with multiple devices connected to that switch. That happens in real networks when users decide they need more ports at their desk. However, the default setting of switchport port-security maximum 1 means that a frame from the second unique source MAC address would cause a violation, and with the default violation action, to err-disable the port.

For the other incorrect answer, the configuration does not prevent unknown MAC addresses from accessing the port because the configuration does not predefine any MAC address.

3. B and C. IOS adds MAC addresses configured by the port security feature as static MAC addresses, so they do not show up in the output of the show mac address-table dynamic command. show mac address-table port-security is not a valid command.

4. B. The question states that the port security status is secure-shutdown. This state is used only by the shutdown port security mode, and when used, it means that the interface has been placed into an err-disabled state. Those facts explain why the correct answer is correct and two of the incorrect answers are incorrect.

The incorrect answer that mentions the violation counter is incorrect because in shutdown mode, the counter no longer increments once the interface is placed into secureshutdown mode, and it resets to 0 once the interface is reset with the shutdown and then no shutdown commands.

5. B and C. First, about the two incorrect answers: In restrict mode, the arrival of a frame that violates the port security policy does not cause the switch to put the interface into err-disabled state. It does cause the switch to discard any frames that violate the policy, but it leaves the interface up and does not discard frames that do not violate the security policy, like the second frame that arrives.

Regarding the two correct answers, a port in port security restrict does cause the switch to issue log messages for a violating frame, send SNMP traps about that same event (if SNMP is configured), and increment the counter of violating frames.

Chapter 7

1. B and D. The client sends a Discover message, with the server returning an Offer message. The client then sends a Request, with the server sending back the IP address in the Acknowledgment message.

2. A and B. The two correct answers list the two primary facts that impact which IP addresses the server will lease to clients. For the incorrect answer about DNS servers, the DHCP server does supply the IP address of the DNS servers, but not the hostnames of the DNS servers. Also, the DHCP server supplies the IP address (but not the MAC address) of the default gateway in each subnet.

3. A and C. A router needs to act as a DHCP relay agent if DHCP clients exist on the connected subnet and there is no DHCP server in that subnet. If a DHCP exists in the subnet, the router does not need to forward DHCP messages to a remote DHCP server (which is the function of a DHCP relay agent). The answer that mentions the ip address dhcp command makes the router interface act as a DHCP client and has nothing to do with DHCP relay agent.

4. D. The ip address dhcp command tells the router to obtain its address using DHCP. The router learns all the same information that a normal DHCP client would learn. The router uses the address listed as the default gateway to build a default route, using the default gateway IP address as the next-hop address. The router continues to work like a router always does, forwarding packets based on its IP routing table.

5. B and C. The output shows the MAC address, IP address, subnet mask (in hex format), and the subnet broadcast address. Of those, the DHCP server supplies the information in the two correct answers. The two incorrect answers mention the MAC address (not supplied by DHCP, but known to the device’s NIC) and the subnet broadcast address (calculated by the host).

6. D. Windows supports both ipconfig and ipconfig /all commands, but the ipconfig command does not mention the DNS servers. Note that the ifconfig command works on Linux and macOS, and the ifconfig /all command is an invalid command.

Chapter 8

1. A and C. DHCP Snooping must be implemented on a device that performs Layer 2 switching. The DHCP Snooping function needs to examine DHCP messages that flow between devices within the same broadcast domain (VLAN). Layer 2 switches, as well as multilayer switches, perform that function. Because a router performs only Layer 3 forwarding (that is, routing) and does not forward messages between devices in the same VLAN, a router does not provide a good platform to implement DHCP Snooping (and is not even a feature of Cisco IOS on routers). End-user devices would be a poor choice as a platform for DHCP Snooping because they would not receive all the DHCP messages, nor would they be able to prevent frames from flowing should an attack occur.

2. B and C. Switch ports connected to IT-controlled devices from which DHCP server messages may be received should be trusted by the DHCP Snooping function. Those devices include IT-controlled DHCP servers and IT-controlled routers and switches. All devices that are expected to be DHCP client devices (like PCs) are then treated as untrusted, because DHCP Snooping cannot know beforehand from which ports a DHCP-based attack will be launched. In this case, the ports connected to all three PCs will be treated as untrusted by DHCP Snooping.

3. C and D. Because of a default setting of untrusted, the switch does not need any configuration commands to cause a port to be untrusted. Of the two (incorrect) answers that related to the trust state, no ip dhcp snooping trust, in interface config mode, would revert from a trust configuration state to an untrusted state. The other answer, ip dhcp snooping untrusted, is not a valid command.

The two correct answers list a pair of configuration commands that both must be included to enable DHCP Snooping (ip dhcp snooping) and to specify the VLAN list on which DHCP Snooping should operate (ip dhcp snooping vlan 5).

4. A. All the answers list commands with correct syntax that are useful for DHCP Snooping; however, the correct answer, no ip dhcp snooping information, disables DHCP Snooping’s feature of adding DHCP Option 82 fields to DHCP messages. This setting is useful if the switch does not act as a DHCP relay agent. The opposite setting (without the no to begin the command) works when the multilayer switch acts as a DHCP relay agent.

5. B. DAI always uses a core function that examines incoming ARP messages, specifically the ARP message origin hardware and origin IP address fields, versus tables of data in the switch about correct pairs of MAC and IP addresses. DAI on a switch can use DHCP Snooping’s binding table as the table of data with valid MAC/IP address pairs or use the logic in configured ARP ACLs. The question stem states that DAI uses DHCP Snooping, so the correct answer notes that the switch will compare the ARP message’s origin hardware address to the switch’s DHCP Snooping binding table.

One incorrect answer mentions a comparison of the message’s ARP origin MAC (hardware) address with the message’s Ethernet source MAC address. DAI can perform that check, but that feature can be configured to be enabled or disabled, so DAI would not always perform this comparison. The other incorrect answers list logic never performed by DAI.

6. B and D. Because of a default setting of untrusted, the switch must be configured so DAI trusts that one port. To add that configuration, the switch needs the ip arp inspection trust command in interface config mode. The similar (incorrect) answer of no ip arp inspection untrust is not a valid command.

To enable DAI for operation on a VLAN, the configuration needs one command: the ip arp inspection vlan 6 command. This command both enables DAI and does so specifically for VLAN 6 alone. The answer ip arp inspection shows a command that would be rejected by the switch as needing more parameters.

7. C and D. With DAI, you can set a limit on the number of received ARP messages with a default burst interval of 1 second, or you can configure the burst interval. Once configured, DAI allows the configured number of ARP messages over the burst interval number of seconds. With the two correct answers, one shows 16 ARP messages, with a 4-second interval, for an average of 4 per second. The other correct answer shows a limit of 4, with the default burst interval of 1 second, for an average of 4. The two incorrect answers result in averages of 2 per second and 5 per second.

Chapter 9

1. D. By default, all message levels are logged to the console on a Cisco device. To do so, IOS uses logging level 7 (debugging), which causes IOS to send severity level 7, and levels below 7, to the console. All the incorrect answers list levels below level 7.

2. C. The logging trap 4 command limits those messages sent to a syslog server (configured with the logging host ip-address command) to levels 4 and below, thus 0 through 4.

3. A. NTP uses protocol messages between clients and servers so that the clients can adjust their time-of-day clock to match the server. NTP is totally unrelated to serial line clocking. It also does not count CPU cycles, instead relying on messages from the NTP server. Also, the client defines the IP address of the server and does not have to be in the same subnet.

4. C. The ntp server command tells the router to be both an NTP server and client. However, the router first acts as an NTP client to synchronize its time with NTP server Once synchronized, R1 knows the time to supply and can act as an NTP server.

5. E and F. CDP discovers information about neighbors. show cdp gives you several options that display more or less information, depending on the parameters used.

6. E and F. The show lldp neighbors command lists one line of output per neighbor. However, it does list the platform information of the neighbor, which typically includes the hardware model number. The show lldp entry Hannah command lists a group of messages about the neighboring router, including more detail about the hardware model and the IOS version.

Chapter 10

1. D. CIDR’s original intent was to allow the summarization of multiple Class A, B, and C networks to reduce the size of Internet routing tables. Of the answers, only summarizes multiple networks.

2. B and E. RFC 1918 identifies private network numbers. It includes Class A network, Class B networks through, and Class C networks through

3. C. With static NAT, the entries are statically configured. Because the question mentions translation for inside addresses, the inside keyword is needed in the command.

4. A. With dynamic NAT, the entries are created as a result of the first packet flow from the inside network.

5. A. The list 1 parameter references an IP ACL, which matches packets, identifying the inside local addresses.

6. A and C. The configuration is missing the overload keyword in the ip nat inside source command and in the ip nat outside interface subcommand on the serial interface.

7. B. The last line mentions that the pool has seven addresses, with all seven allocated, with the misses counter close to 1000—meaning that close to 1000 new flows were rejected because of insufficient space in the NAT pool

Chapter 11

1. A, B, and E. QoS tools manage bandwidth, delay, jitter, and loss.

2. B and C. The Class of Service (CoS) field exists in the 802.1Q header, so it would be used only on trunks, and it would be stripped of the incoming data-link header by any router in the path. The MPLS EXP bits exist as the packet crosses the MPLS network only. The other two fields, IP Precedence (IPP) and Differentiated Services Code Point (DSCP), exist in the IP header and would flow from source host to destination host.

3. A, B, and C. In general, matching a packet with DiffServ relies on a comparison to something inside the message itself. The 802.1p CoS field exists in the data-link header on VLAN trunks; the IP DSCP field exists in the IP header; and extended ACLs check fields in message headers. The SNMP Location variable does not flow inside individual packets but is a value that can be requested from a device.

4. B and C. Low Latency Queuing (LLQ) applies priority queue scheduling, always taking the next packet from the LLQ if a packet is in that queue. To prevent queue starvation of the other queues, IOS also applies policing to the LLQ. However, applying shaping to an LLQ slows the traffic, which makes no sense with the presence of a policing function already.

5. A and D. Policers monitor the bit rate and take action if the bit rate exceeds the policing rate. However, the action can be to discard some packets, or to re-mark some packets, or even to do nothing to the packets, simply measuring the rate for later reporting. For shaping, when a shaper is enabled because the traffic has exceeded the shaping rate, the shaper always queues packets and slows the traffic. There is no option to re-mark the packets or to bypass the shaping function.

6. C and D. Drop management relies on the behavior of TCP, in that TCP connections slow down sending packets due to the TCP congestion window calculation. Voice traffic uses UDP, and the question states that queue 1 uses UDP. So, queues 2 and 3 are reasonable candidates for using a congestion management tool.

Chapter 12

1. D. With this design but no FHRP, host A can send packets off-subnet as long as connectivity exists from host A to R1. Similarly, host B can send packets off-subnet as long as host B has connectivity to router R2. Both routers can attach to the same LAN subnet and basically ignore each other in relation to their roles as default router because they do not use an FHRP option. When either router fails, the hosts using that router as default router have no means by which to fail over.

2. C. The use of an FHRP in this design purposefully allows either router to fail and still support off-subnet traffic from all hosts in the subnet. Both routers can attach to the same LAN subnet per IPv4 addressing rules.

3. C. HSRP uses a virtual IP address. The virtual IP address comes from the same subnet as the routers’ LAN interfaces but is a different IP address than the router addresses configured with the ip address interface subcommand. As a result, the hosts will not point to or in this design. The other wrong answer lists an idea of using the Domain Name System (DNS) to direct hosts to the right default router; although this idea exists in some other forms of network load balancing, it is not a part of any of the three FHRP protocols.

4. B. SNMPv1 and SNMPv2c use community strings to authenticate Get and Set messages from an NMS. The agent defines a read-only community and can define a readwrite community as well. Get requests, which read information, will be accepted if the NMS sends either the read-only or the read-write community with those requests.

5. A and C. SNMP agents reside on a device being managed. When an event happens about which the device wants to inform the SNMP manager, the agent sends either an SNMP Trap or SNMP Inform to the SNMP manager. The SNMP manager normally sends an SNMP Get Request message to an agent to retrieve MIB variables or an SNMP Set Request to change an MIB variable on the agent.

6. A. FTP uses both a control connection and a data connection. The FTP client initiates the control connection. However, in active mode, the FTP server initiates the data connection. Also, note that FTP does not use TLS, while FTP Secure (FTPS) does use TLS.

7. B and D. TFTP supports fewer functions than FTP as a protocol. For instance, the client cannot change the current directory on the server, add directories, remove directories, or list the files in the directory. Both TFTP and FTP support the ability to transfer files in either direction.

Chapter 13

1. B and D. The access layer switches play the role of connecting to the endpoint devices, whether they are end-user devices or servers. Then, from the access to the distribution layer, each access layer connects to two distribution switches typically, but with no direct connections between access layer switches, creating a mesh (but a partial mesh). A two-tier design, also called a collapsed core, does not use core switches at all.

2. A and C. The access layer switches, not the distribution layer switches, play the role of connecting to the endpoint devices, whether they are end-user devices or servers. Then, from the access to the distribution layer, each access layer connects to two distribution switches typically, but with no direct connections between access layer switches, creating a mesh (but a partial mesh). A three-tier design, also called a core design, does use core switches, with a partial mesh of links between the distribution and core switches. Basically, each distribution switch connects to multiple core switches but often does not connect directly to other distribution switches.

3. D. The access layer uses access switches, which connect to endpoint devices. A single access switch with its endpoint devices looks like a star topology. The distribution layer creates a partial mesh of links between the distribution switches and access switches, so it is neither a full mesh nor a hybrid.

4. A and C. With a SOHO LAN, one integrated device typically supplies all the necessary functions, including routing, switching, wireless access point (AP), and firewall. The AP uses standalone mode, without a wireless LAN controller (WLC), and without a need to encapsulate frames in CAPWAP.

5. A. First, the switch does not supply power based on a configured value to avoid the unfortunate case of supplying power over the cable to a device that does not support the circuitry to receive the power, because doing so will likely harm the electronics on the connected device.

If configured to use PoE, the switch begins with IEEE autonegotiation messages while sensing the load on the circuit, which indicates whether the device desires to receive power, and indicates the power class desired (which dictates the amount of power to initially deliver). Note that once the attached device (called the powered device, or PD) boots, the PD can request additional power using CDP and/or LLDP.

6. B and D. Universal Power over Ethernet (UPoE) and the enhanced UPoE Plus (UPoE+) supply power over all four pairs of the cable. Note that 1000BASE-T and faster UTP-based Ethernet standards often require four pair, whereas earlier/slower standards did not, and UPoE/UPoE+ take advantage of the existence of four pairs to supply power over all four pairs. Power over Ethernet (PoE) and PoE+ use two pairs for power and therefore work with Ethernet standards like 10BASE-T and 100BASE-T that use two pairs only.

Chapter 14

1. B and C. A Metro Ethernet E-Tree service uses a rooted point-to-multipoint Ethernet Virtual Connection (EVC), which means that one site connected to the service (the root) can communicate directly with each of the remote (leaf) sites. However, the leaf sites cannot send frames directly to each other; they can only send frames to the root site. Topology design like this that allows some but not all pairs of devices in the group to communicate is called a partial mesh, or hub and spoke, or in some cases a multipoint or point-to-multipoint topology.

Of the incorrect answers, the full mesh term refers to topology designs in which each pair in the group can send data directly to each other, which is typical of a MetroE E-LAN service. The term point-to-point refers to topologies with only two nodes in the design, and they can send directly to each other, typical of a MetroE E-Line service.

2. A. Metro Ethernet uses Ethernet access links of various types. Time-division multiplexing (TDM) links such as serial links, even higher-speed links like T3 and E3, do not use Ethernet protocols, and are less likely to be used. MPLS is a WAN technology that creates a Layer 3 service.

Two answers refer to Ethernet standards usable as the physical access link for a Metro Ethernet service. However, 100BASE-T supports cable lengths of only 100 meters, so it is less likely to be used as a Metro Ethernet access link in comparison to 100BASE-LX10, which supports lengths of 10 km.

3. A and D. An E-LAN service is one in which the Metro Ethernet service acts as if the WAN were a single Ethernet switch so that each device can communicate directly to every other device. As a result, the routers sit in the same subnet. With one headquarters router and 10 remote sites, each router will have 10 OSPF neighbors.

4. B and C. A Layer 3 MPLS VPN creates an IP service with a different subnet on each access link. With one headquarters router and 10 remote sites, 11 access links exist, so 11 subnets are used.

As for the OSPF neighbor relationships, each enterprise router has a neighbor relationship with the MPLS provider edge (PE) router, but not with any of the other enterprise (customer edge) routers. So each remote site router would have only one OSPF neighbor relationship.

5. D. Architecturally, MPLS allows for a wide variety of access technologies. Those include TDM (that is, serial links), Frame Relay, ATM, Metro Ethernet, and traditional Internet access technologies such as DSL and cable.

6. A. The PE-CE link is the link between the customer edge (CE) router and the MPLS provider’s provider edge (PE) router. When using OSPF, that link will be configured to be in some area. OSPF design allows for that link to be in the backbone area, or not, through the use of the OSPF super backbone, which exists between all the PE routers.

7. A. The term remote access VPN, or client VPN, typically refers to a VPN for which one endpoint is a user device, such as a phone, tablet, or PC. In those cases, TLS is the more likely protocol to use. TLS is included in browsers, and is commonly used to connect securely to websites. GRE along with IPsec is more likely to be used to create a site-to-site VPN connection. FTPS refers to FTP Secure, which uses TLS to secure FTP sessions.

Chapter 15

1. A, B, and E. The hypervisor will virtualize RAM, CPU, NICs, and storage for each VM. The hypervisor itself is not virtualized, but rather does the work to virtualize other resources. Also, as virtual machines, the VMs do not use power, so the power is not virtualized.

2. D. Hypervisors create a virtual equivalent of Ethernet switching and cabling between the VMs and the physical NICs. The VMs use a virtual NIC (vNIC). The hypervisor uses a virtual switch (vswitch), which includes the concept of a link between a vswitch port and each VM’s vNIC. The vswitch also connects to both physical NICs. The switch can then be configured to create VLANs and trunks as needed.

3. B. Platform as a Service (PaaS) supplies one or more virtual machines (VMs) that have a working operating system (OS) as well as a predefined set of software development tools.

As for the wrong answers, Software as a Service (SaaS) supplies a predefined software application, but typically with no ability to then later install your own applications. Infrastructure as a Service (IaaS) supplies one or more working VMs, optionally with an OS installed, so it could be used for software development, but the developer would have to install a variety of development tools, making IaaS less useful than a PaaS service. Finally, Server Load Balancing as a Service (SLBaaS) can be offered as a cloud service, but it is not a general service in which customers get access to VMs on which they can then install their own applications.

4. A. Infrastructure as a Service (IaaS) supplies one or more working virtual machines (VMs), optionally with an OS installed, as a place where you can then customize the systems by installing your own applications.

Software as a Service (SaaS) supplies a predefined software application, but typically with no ability to then later install your own applications. Platform as a Service (PaaS) could be used to install your own application, because PaaS does supply one or more VMs, but it is most likely used as a software development environment, a service designed specifically to be used for development, with VMs that include various tools that are useful for software development. Finally, Server Load Balancing as a Service (SLBaaS) can be offered as a cloud service, but it is not a general service in which customers get access to VMs on which they can then install their own applications.

5. A. Both options that use the Internet allow for easier migration because public cloud providers typically provide easy access over the Internet. An intercloud exchange is a purpose-built WAN service that connects to enterprises as well as most public cloud providers, with the advantage of making the cloud migration process easier. The one correct answer—the worst option in terms of being prepared for migrating to a new cloud provider—is to use a private WAN connection to one cloud provider. While useful in other ways, migrating when using this strategy would require installing a new private WAN connection to the new cloud provider.

6. A and C. Private WAN options use technologies like Ethernet WAN and MPLS, both of which keep data private by their nature and which include QoS services. An intercloud exchange is a purpose-built WAN service that connects to enterprises as well as most public cloud providers, using the same kinds of private WAN technology with those same benefits.

For the two incorrect answers, both use the Internet, so both cannot provide QoS services. The Internet VPN option does encrypt the data to keep it private.

Chapter 16

1. A. The data plane includes all networking device actions related to the receipt, processing, and forwarding of each message, as in the case described in the question. The term table plane is not used in networking. The management plane and control plane are not concerned with the per-message forwarding actions.

2. C. The control plane includes all networking device actions that create the information used by the data plane when processing messages. The control plane includes functions like IP routing protocols and Spanning Tree Protocol (STP).

The term table plane is not used in networking. The management plane and data plane are not concerned with collecting the information that the data plane then uses.

3. C. Although many variations of SDN architectures exist, they typically use a centralized controller. That controller may centralize some or even all control plane functions in the controller. However, the data plane function of receiving messages, matching them based on header fields, taking actions (like making a forwarding decision), and forwarding the message still happens on the network elements (switches) and not on the controller.

For the incorrect answers, the control plane functions may all happen on the controller, or some may happen on the controller, and some on the switches. The northbound and southbound interfaces are API interfaces on the controller, not on the switches.

4. A. The OpenDaylight Controller uses an Open SDN model with an OpenFlow southbound interface as defined by the Open Networking Foundation (ONF). The ONF SDN model centralizes most control plane functions. The APIC model for data centers partially centralizes control plane functions. The APIC-EM controller (as of time of publication) makes no changes to the control plane of routers and switches, leaving those to run with a completely distributed control plane.

5. C and D. ACI uses a spine-leaf topology. With a single-site topology, leaf switches must connect to all spine switches, and leaf switches must not connect to other leaf switches. Additionally, a leaf switch connects to some endpoints, with the endpoints being spread across the ports on all the leaf switches. (In some designs, two or more leaf switches connect to the same endpoints for redundancy and more capacity.)

6. A and D. Controller-based networks use a controller that communicates with each network device using a southbound interface (an API and protocol). By gathering network information into one central device, the controller can then allow for different operational models. The models often let the operator think in terms of enabling features in the network, rather than thinking about the particulars of each device and command on each device. The controller then configures the specific commands, resulting in more consistent device configuration.

For the incorrect answers, both the old and new models use forwarding tables on each device. Also, controllers do not add to or remove from the programmatic interfaces on each device, some of which existed before controllers, but rather supply useful and powerful northbound APIs.

Chapter 17

1. C. The SDA underlay consists of the network devices and connections, along with configuration that allows IP connectivity between the SDA nodes, for the purpose of supporting overlay VXLAN tunnels. The fabric includes both the underlay and overlay, while VXLAN refers to the protocol used to create the tunnels used by the overlay.

2. B. The overlay includes the control plane and data plane features to locate the endpoints, decide to which fabric node a VXLAN tunnel should connect, direct the frames into the tunnel, and perform VXLAN tunnel encapsulation and de-encapsulation. The SDA underlay exists as network devices, links, and a separate IP network to provide connectivity between nodes to support the VXLAN tunnels.

The fabric includes both the underlay and overlay, while VXLAN refers to the protocol used to create the tunnels used by the overlay.

3. D. The SDA overlay creates VXLAN tunnels between SDA edge nodes. Edge nodes then create a data plane by forwarding frames sent by endpoints over the VXLAN tunnels. LISP plays a role in the overlay as the control plane, which learns the identifiers of each endpoint, matching the endpoint to the fabric node that can teach the endpoint, so that the overlay knows where to create VXLAN tunnels.

For the other incorrect answers, note that while GRE is a tunneling protocol, SDA uses VXLAN for tunneling, and not GRE. Finally, OSPF acts as a control plane routing protocol, rather than a data plane protocol for SDA.

4. A and D. As with any SDA feature, the configuration model is to configure the feature using DNA Center, with DNA Center using southbound APIs to communicate the intent to the devices. The methods to configure the feature using DNA Center include using the GUI or using the northbound REST-based API.

Of the incorrect answers, you would not normally configure any of the SDA devices directly. Also, while DNA Center can use NETCONF as a southbound protocol to communicate with the SDA fabric nodes, it does not use NETCONF as a northbound API for configuration of features.

5. B, C, and D. Cisco DNA Center manages traditional network devices with traditional protocols like Telnet, SSH, and SNMP. DNA Center can also use NETCONF and RESTCONF if supported by the device. Note that while useful tools, Ansible and Puppet are not used by DNA Center.

6. A and D. Traditional network management platforms can do a large number of functions related to managing traditional networks and network devices, including the items listed in the two correct answers. However, when using Cisco’s Prime Infrastructure as a traditional network management platform for comparison, it does not support SDA configuration, nor does it find the end-to-end path between two endpoints and analyze the ACLs in the path. Note that the two incorrect answers reference features available in DNA Center.

Chapter 18

1. B and D. The six primary required features of REST-based APIs include three features mentioned in the answers: a client/server architecture, stateless operation, notation of whether each object is cacheable. Two items from these three REST attributes are the correct answers. Of the incorrect answers, classful operation is the opposite of the REST-based API feature of classless operation. For the other incorrect answer, although many REST-based APIs happen to use HTTP, REST APIs do not have to use HTTP.

2. B and D. In the CRUD software development acronym, the matching terms (create, read, update, delete) match one or more HTTP verbs. While the HTTP verbs can sometimes be used for multiple CRUD actions, the following are the general rules: create performed by HTTP POST; read by HTTP GET; update by HTTP PATCH, PUT (and sometimes POST); delete by HTTP DELETE.

3. C. The URI for a REST API call uses a format of protocol://hostname/resource?parameters. The API documentation details the resource part of the URI, as well as any optional parameters. For instance, in this case, the resource section is /dna/intent/api/v1/network-device. Additionally, the API documentation for this resource details optional parameters in the query field as listed after the ? in the URI.

4. A and D. Of the four answers, two happen to be most commonly used to format and serialize data returned from a REST API: JSON and XML. For the incorrect answers, JavaScript is a programming language that first defined JSON as a data serialization language. YAML is a data serialization/modeling language and can be found most often in configuration management tools like Ansible.

5. A and D. JSON defines variables as key:value pairs, with the key on the left of the colon (:) and always enclosed in double quotation marks, with the value on the right. The value can be a simple value or an object or array with additional complexity. The number of objects is defined by the number of matched curly brackets ({ and }), so this example shows a single JSON object.

The one JSON object shown here includes one key and one :, so it has a single key:value pair (making one answer correct). The value in that key:value pair itself is a JSON array (a list in Python) that lists numbers 1, 2, and 3. The fact that the list is enclosed in square brackets defines it as a JSON array.

6. C and D. To interpret this JSON data, first look for the innermost pairing of either curly brackets { }, which denote one object, or square brackets [ ], which denote one array. In this case, the gray highlighted area is one JSON object, enclosed with { } and no other brackets of either type inside. That makes the gray area one object, which itself holds key:value pairs.

Inside that one object, four key:value pairs exist, with the key before each colon and the value after each colon. That means “type” is a key, and “ACCESS” is one of the values.

If you look at the other pair of curly brackets that begin and end the JSON data, that pair defines an object. That object has a key of “response” (making one answer incorrect). The “response” key then has a value equal to the entire inner object (the gray highlighted part), confirming one of the correct answers.

Chapter 19

1. C. Devices with the same role in an enterprise should have a very similar configuration. When engineers make unique changes on individual devices—different changes from those made in the majority of devices with that same role—those devices’ configurations become different than the intended ideal configuration for every device with that role. This effect is known as configuration drift. Configuration management tools can monitor a device’s configuration versus a file that shows the intended ideal configuration for devices in that role, noting when the device configuration drifts away from that ideal configuration.

2. A and B. The version control system, applied to the centralized text files that contain the device configurations, automatically tracks changes. That means the system can see which user edited the file, when, and exactly what change was made, with the ability to make comparisons between different versions of the files.

The two incorrect answers list very useful features of a configuration management tool, but those answers list features typically found in the configuration management tool itself rather than in the version control tool.

3. D. Configuration monitoring (a generic description) refers to a process of checking the device’s actual configuration versus the configuration management system’s intended configuration for the device. If the actual configuration has moved away from the intended configuration—that is, if configuration drift has occurred—configuration monitoring can either reconfigure the device or notify the engineering staff.

For the other answers, two refer to features of the associated version control software typically used along with the configuration management tool. Version control software will track the identity of each user who changes files and track the differences in files over time. The other incorrect answer is a useful feature of many configuration management tools, in which the tool verifies that the configuration will be accepted when attempted (or not). However, that useful feature is not part of what is called configuration monitoring.

4. A. Ansible uses a push model, in which the Ansible control node decides when to configure a device based on the instructions in a playbook. Puppet and Chef use pull models, in which an agent asks for information from a server, with the agent then making the decision of whether it needs to pull configuration data to itself and reconfigure itself.

5. B and C. Of the terms manifest and recipe, both refer to files that define the actions to take and/or the end state desired when taking action in one of the configuration management tools. These files go by the names Ansible playbook, Puppet manifest, and Chef recipe.

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