Question 1

A Cisco router has learned three different routes to the same destination network. An EIGRP route has a composite metric of 20684570, an OSPF route has a metric cost of 852, and a RIPv2 route has a hop count of 4. Based on default administrative dis…

Accepted Answer

Introduction / Context: This question evaluates your understanding of how Cisco routers choose between multiple routes to the same destination network when those routes are learned from different routing protocols. It is important to know that before comparing protocol specific metrics such as EIGRP composite cost, OSPF cost, or RIP hop count, the router first uses the concept of administrative distance to determine which routing source is considered the most trustworthy by default. Given Data / Assumptions: - One route comes from EIGRP with a composite metric of 20684570. - One route comes from OSPF with a metric value of 852. - One route comes from RIPv2 with a hop count metric of 4. - All three routes describe the same destination network prefix. - Default Cisco administrative distances are in use: EIGRP internal 90, OSPF 110, RIPv2 120. Concept / Approach: Administrative distance represents the trust level of a routing information source. Lower administrative distance values are preferred over higher values. Cisco routers compare administrative distance before comparing metrics within a single protocol. EIGRP internal routes have an administrative distance of 90, OSPF has 110, and RIPv2 has 120 by default. Because 90 is the lowest among these, the EIGRP route will be selected without even considering the detailed metric values. The specific composite, cost, or hop count values only come into play when comparing routes from the same routing protocol. Step-by-Step Solution: Step 1: Write down the default administrative distances: EIGRP internal 90, OSPF 110, RIPv2 120.Step 2: Note that all three routes point to the same destination prefix, so administrative distance must be used to pick between protocols.Step 3: Compare the distances. The smallest value among 90, 110, and 120 is 90 for EIGRP.Step 4: Conclude that the EIGRP route is preferred over OSPF and RIPv2 because it has the most trustworthy source by default.Step 5: Recognize that the exact EIGRP composite metric of 20684570, the OSPF cost of 852, and the RIP hop count of 4 are not cross compared because they are from different protocols. Verification / Alternative check: A quick verification approach is to remember the common ordering of default administrative distances on Cisco equipment: connected 0, static 1, EIGRP internal 90, IGRP 100, OSPF 110, IS IS 115, RIP 120, and EIGRP external 170. In that sorted list EIGRP internal appears before OSPF and RIPv2, confirming that the EIGRP route is the one that will be installed into the routing table. Why Other Options Are Wrong: The option claiming that only the OSPF route will be installed ignores the fact that OSPF has a higher administrative distance than EIGRP. The choice that only the RIPv2 route is installed is incorrect since RIP has the highest distance of the three. Installing all three routes and load balancing would only occur if the routes came from the same protocol and had equal administrative distance and metric values. A combination of OSPF and RIPv2 routes is also invalid when an EIGRP route with a better distance is available. Common Pitfalls: A very common mistake is to compare the protocol specific metric values directly, such as 4 hops versus an OSPF cost of 852, which simply does not make sense because they are on different scales. Another pitfall is forgetting the actual default administrative distance values and assuming that newer protocols always win. Memorizing the relative ordering of distances is usually enough to answer many exam questions quickly and accurately. Final Answer: Only the EIGRP route will be installed in the routing table because it has the lowest default administrative distance.

Question 2

In the four layer TCP IP reference model that underlies the Internet, which TCP IP layer is functionally equivalent to the Transport layer of the seven layer OSI model?

Accepted Answer

Introduction / Context: This question examines your ability to relate the traditional seven layer OSI model to the four layer TCP IP model that is used in most real world networking discussions. Specifically it checks whether you know which TCP IP layer lines up with the Transport layer of the OSI model, where Transmission Control Protocol and User Datagram Protocol operate to provide end to end communication between hosts. Given Data / Assumptions: - The OSI Transport layer is Layer 4 and provides end to end transport services, segmentation, and reassembly. - The TCP IP model has four conceptual layers: Application, Host to Host, Internet, and Network Access, though names can vary slightly across sources. - Protocols such as TCP and UDP belong to the Transport layer in the OSI view. - The task is to choose the TCP IP layer that offers equivalent functionality. Concept / Approach: In the TCP IP model, the Host to Host layer is responsible for providing reliable or unreliable end to end delivery between hosts, handling tasks such as segmentation, acknowledgments, and flow control. This is where TCP and UDP live. These responsibilities match those of the OSI Transport layer, which focuses on transport related services rather than routing or media access. The Internet layer of the TCP IP model corresponds more closely to the OSI Network layer, and the Network Access layer groups functions of the OSI Data Link and Physical layers. Step-by-Step Solution: Step 1: Identify that TCP and UDP are the central protocols at the Transport layer in the OSI model.Step 2: Recall that in the TCP IP model TCP and UDP sit at the Host to Host layer, which is sometimes also called the Transport layer in that simplified model.Step 3: Confirm that the Internet layer in TCP IP is primarily responsible for routing and logical addressing, which aligns with the OSI Network layer, not with the OSI Transport layer.Step 4: Recognize that the Network Access layer in TCP IP combines the roles of the Data Link and Physical layers and deals with hardware addressing and signaling.Step 5: Conclude that the Host to Host layer is the correct match for the OSI Transport layer. Verification / Alternative check: A simple cross reference table can help. Application, Presentation, and Session layers in OSI map roughly to the Application layer in TCP IP. The OSI Transport layer matches the Host to Host or Transport layer in TCP IP. The OSI Network layer matches the Internet layer. Finally the Data Link and Physical layers map to the Network Access layer. This mapping confirms that Host to Host is the correct answer for the OSI Transport layer equivalence. Why Other Options Are Wrong: The Application layer of TCP IP groups multiple upper OSI layers and hosts protocols like HTTP and FTP, not core transport functions. The Internet layer handles IP addressing and routing decisions, so it corresponds to the OSI Network layer. The Network Access and Link layer options refer to lower level media and framing details corresponding to OSI Layers 1 and 2, not to end to end transport services. Common Pitfalls: Learners sometimes confuse the Host to Host and Internet layers because both are involved in moving traffic between machines. Remember that Host to Host cares about communication between processes on end systems using ports and reliability mechanisms, while the Internet layer cares about moving packets from one network to another using IP addresses. Another pitfall is thinking that the OSI and TCP IP models line up layer by layer, when in reality the TCP IP stack compresses functionality into fewer layers. Final Answer: The Host to Host layer in the TCP IP model is equivalent to the Transport layer in the OSI model.

Question 3

A network administrator working on a personal computer named PC1 opens a command prompt and issues the command ping 127.0.0.1. If an ICMP echo reply is received from this ping, what does this result actually confirm about the system?

Accepted Answer

Introduction / Context: This question focuses on the use of the loopback address 127.0.0.1 and the ping utility as a basic troubleshooting tool. Many technicians use ping to test network connectivity, but it is important to understand exactly what is being tested when you ping the loopback address rather than a remote host or default gateway. Knowing the difference helps you interpret ping results correctly during diagnostics. Given Data / Assumptions: - The host is a personal computer called PC1 running a TCP IP capable operating system. - The administrator runs the command ping 127.0.0.1 at a command prompt. - An Internet Control Message Protocol echo reply is received in response. - No information is given about remote network devices or default gateways. Concept / Approach: The IPv4 address 127.0.0.1 is the standard loopback address reserved for testing the local protocol stack. When an application or the ping utility sends packets to this address, the data never leaves the local host. Instead, the packets are processed internally by the operating system network stack. If the ping to 127.0.0.1 succeeds, it proves that the TCP IP protocol suite is installed, properly bound to the network interface subsystem, and functioning at least at the local loopback level. It does not confirm that any external network interface or remote path is working. Step-by-Step Solution: Step 1: Recognize that 127.0.0.1 is a special loopback address defined for local host testing.Step 2: Understand that sending a ping to 127.0.0.1 sends ICMP packets that are processed internally by the TCP IP stack of PC1.Step 3: When an echo reply is received, it indicates that packet creation, internal routing, and protocol handling all operate correctly on the host.Step 4: Note that no external router, switch, or gateway is involved in this communication because the loopback address is never forwarded on the network.Step 5: Conclude that the only confirmed fact is that the TCP IP stack is installed and functioning locally. Verification / Alternative check: To test remote connectivity, you would instead ping the default gateway or another reachable host on the same subnet. If those pings fail while ping 127.0.0.1 still works, you have isolated the issue to something between the network interface and the external network, such as cabling, Network Interface Card failure, incorrect IP configuration, or switch problems. This comparison shows that loopback testing is much more limited in scope than external connectivity testing. Why Other Options Are Wrong: Claiming that PC1 has connectivity with another local host is incorrect because the ping never leaves PC1. Saying that PC1 has connectivity with the default gateway is also wrong for the same reason. End to end connectivity to remote Layer 3 devices across the Internet cannot be inferred from a local loopback ping. Firewall rules allowing outbound traffic are unrelated to this test because the traffic never passes through an external firewall interface. Common Pitfalls: A frequent mistake is to assume that a successful loopback ping guarantees full network connectivity. In reality, it only proves that the internal protocol stack is functional. Another pitfall is to overlook the loopback test altogether and waste time troubleshooting hardware when the TCP IP stack itself is misconfigured or not installed. Using 127.0.0.1 as a first check is an efficient diagnostic practice but its scope must be understood. Final Answer: A successful ping to 127.0.0.1 confirms that the TCP IP protocol stack on PC1 is correctly installed and functioning on the local machine.

Question 4

Which of the following options describes an industry wide suite of protocols and algorithms that provides secure data transmission over an IP based network and operates at the Network layer layer 3 of the OSI model?

Accepted Answer

Introduction / Context: This security focused question tests your ability to identify the protocol suite that provides encryption, authentication, and integrity services for IP traffic at the Network layer. Networking professionals must know that Virtual Private Networks are often implemented using a standard group of protocols designed specifically for secure communications over untrusted networks, and that this group operates at Layer 3 in the OSI model. Given Data / Assumptions: - We are looking for a standards based collection of protocols and algorithms, not a single vendor feature. - The solution provides secure data transmission over an IP based network. - It functions at the OSI Network layer number 3, not at higher or lower layers. - Options include several other protocols and technologies that work at different layers or serve different purposes. Concept / Approach: IP Security, commonly called IPSec, is an industry standard framework for securing IP traffic. It defines protocols such as Authentication Header and Encapsulating Security Payload, key management using Internet Key Exchange, and various cryptographic algorithms. IPSec can provide confidentiality, integrity, and authentication for IP packets and is usually considered a Layer 3 technology because it protects and sometimes encapsulates IP packets themselves. While VPN is a wider concept for creating private connectivity across public networks, IPSec is the specific suite that implements many site to site and remote access VPNs. Step-by-Step Solution: Step 1: Eliminate technologies that do not function at the Network layer or that do not focus on security.Step 2: Recognize that HDLC is a Layer 2 data link protocol used on serial links and does not provide encryption by default.Step 3: Note that xDSL refers to broadband access methods at the Physical and Data Link layers rather than security protocols.Step 4: Understand that VPN is a general term describing private network creation and can be implemented using several technologies such as IPSec, SSL, or Multiprotocol Label Switching.Step 5: Identify IPSec as the explicit industry standard suite of protocols that secures IP traffic and operates logically at the Network layer. Verification / Alternative check: If you recall the common OSI mapping, you know that IPSec encapsulates or authenticates IP packets directly, which is consistent with Layer 3 operation. In contrast, Secure Sockets Layer and Transport Layer Security usually operate at higher layers just above the Transport layer, while protocols like PPP and HDLC work below the Network layer. This confirms that IPSec is the only option that fits both the security focus and the layer requirement in the question. Why Other Options Are Wrong: HDLC is a data link layer protocol used for framing on serial interfaces and does not inherently provide encryption or a full security framework. xDSL technologies are methods of delivering digital data over telephone lines and address physical transport, not IP security. VPN as a general term is too broad and does not name the specific protocol suite. PPP is another data link protocol used for encapsulating network layer protocols over point to point links and is not primarily a security framework. Common Pitfalls: Many learners are tempted to choose VPN because the question mentions secure data transmission and privacy, but VPN describes the overall concept rather than the implementation details. Remember that IPSec is often used under the hood to build VPN tunnels, yet the exam expects you to identify the underlying protocol suite name. Confusing the layer at which each protocol operates is another common issue, especially when terms are used loosely in marketing materials. Final Answer: The correct choice is IP Security IPSec, which is a suite of protocols that secures IP traffic at the Network layer.

Question 5

In a Windows 2000 Active Directory environment, by default what type of trust relationship exists between domains inside the same domain tree or forest?

Accepted Answer

Introduction / Context: This question tests your understanding of how Windows 2000 Active Directory domains relate to one another within a domain tree or forest. Trust relationships determine how authentication requests and user access can flow between domains, which is fundamental for designing and managing enterprise directory structures. Knowing the default trust type is important for both planning and troubleshooting. Given Data / Assumptions: - The environment is specifically Windows 2000, which introduced Active Directory and a new trust model compared to Windows NT. - The domains in question are inside the same domain tree or forest, not part of different forests or external environments. - We are not discussing manually created external or shortcut trusts. - The task is to identify the default trust relationship type among these related domains. Concept / Approach: In Windows 2000 Active Directory, domains in the same tree and forest are automatically connected by two way transitive trusts. A transitive trust means that if Domain A trusts Domain B and Domain B trusts Domain C, then Domain A can transitively trust Domain C. This behavior simplifies authentication across multiple domains in a forest and allows group membership and access control to span domains more naturally. One way and non transitive trusts are still possible but are used mainly for special scenarios or external connections. Step-by-Step Solution: Step 1: Recall that Active Directory reorganized the trust model so that all domains in a forest are linked automatically.Step 2: Recognize that these automatically created trusts are both two way and transitive by default.Step 3: Understand that explicit trusts normally refer to manually created relationships, often with external or legacy domains.Step 4: Note that one way trusts restrict authentication flow to a single direction, which is not the default for domains in the same tree.Step 5: Conclude that transitive trust is the correct answer for default behavior within a Windows 2000 domain tree or forest. Verification / Alternative check: You can verify this by recalling how users in one Active Directory domain can access resources in another domain in the same forest after simple group membership and permission configuration, without manually defining a trust path. This easy access is made possible by the automatic two way transitive trusts. In contrast, when connecting to external forests or legacy NT domains, administrators often have to define explicit or non transitive trusts. Why Other Options Are Wrong: An explicit trust usually refers to a manually created trust, often used for special cross forest or external domain scenarios, not the default inside a forest. One way trust does not match the default two way nature of Windows 2000 domain trusts within a tree. Non transitive trust does not allow trust relationships to extend beyond directly connected domains, which is not how Active Directory trees and forests are designed by default. External forest trust is a specific type of trust used between two different forests and is not applicable for domains already inside the same forest. Common Pitfalls: Candidates sometimes remember only that Windows NT used more limited and manually defined trusts, and they incorrectly apply that memory to Windows 2000. Others confuse transitive behavior with replication or other directory operations. It is important to separate the concept of trust direction and transitivity from concepts such as site replication and group policy inheritance. Final Answer: By default, domains within the same Windows 2000 Active Directory tree or forest are linked by transitive trusts.

Question 6

In large scale Internet environments between autonomous systems, why is Border Gateway Protocol BGP generally preferred for interdomain routing instead of using interior gateway protocols such as OSPF, EIGRP, or RIP?

Accepted Answer

Introduction / Context: This question looks at the design reasons why Border Gateway Protocol is used as the standard exterior gateway protocol on the global Internet. It expects you to understand that interior gateway protocols such as Open Shortest Path First, Enhanced Interior Gateway Routing Protocol, and Routing Information Protocol are optimized for routing within a single administrative domain, while BGP is optimized for policy control and scalability between autonomous systems. Given Data / Assumptions: - The context is interdomain or Internet routing, not small internal campus routing. - Multiple autonomous systems under different administrative control exchange routing information. - The candidate protocols include BGP and several interior gateway protocols such as OSPF, EIGRP, and RIP. - The question asks why BGP is a better choice rather than which algorithm it uses internally. Concept / Approach: BGP is a path vector protocol designed specifically for interdomain routing. It scales to support hundreds of thousands of prefixes and allows network operators to implement complex routing policies. These policies can be based on attributes such as AS path, local preference, and communities, and they allow operators to influence inbound and outbound traffic flows for business, performance, or security reasons. Interior gateway protocols focus on finding shortest paths within an autonomous system and typically assume a single administrative policy, which is quite different from the diverse policies across the Internet. Step-by-Step Solution: Step 1: Recognize that the Internet consists of many autonomous systems that may have conflicting policies about how traffic should enter or leave their networks.Step 2: Recall that BGP includes attributes such as AS path, local preference, MED, and community values to express and enforce these policies.Step 3: Understand that BGP is designed to handle a huge number of routing prefixes and frequent incremental updates without causing excessive flooding.Step 4: Compare this with IGPs, which are optimized for fast convergence and shortest path routing within a single administrative domain, not for policy rich interdomain routing.Step 5: Conclude that BGP is preferred because of its scalability and policy control capabilities rather than simplistic metrics. Verification / Alternative check: You can verify this by considering the full Internet routing table, which contains hundreds of thousands of prefixes. Running a typical link state IGP across all autonomous systems would create massive overhead as topology changes in one organization would have to be flooded globally. Instead, BGP allows each autonomous system to share only necessary path information and to filter, aggregate, or modify routes according to local policy. This design prevents global instability and keeps routing manageable. Why Other Options Are Wrong: Claiming that BGP uses hop count as its only metric is incorrect; that description fits RIP more closely. BGP does not flood link state advertisements in the same way OSPF does; it exchanges path vectors and incremental updates. It also does not automatically redistribute all routes between IGPs without configuration. The statement that BGP operates at the Data Link layer is false, as BGP runs over TCP at higher layers in the protocol stack. Common Pitfalls: A common misunderstanding is to think that BGP is simply another shortest path protocol like OSPF but for the Internet. In reality, BGP is more about policy and scalability than raw speed of convergence. Another pitfall is confusing exterior gateway and interior gateway roles; IGPs are excellent at fast convergence inside an autonomous system, whereas BGP is carefully tuned to limit instability between autonomous systems. Final Answer: BGP is preferred for Internet routing because it supports rich routing policies and scales well to a very large number of prefixes exchanged between autonomous systems.

Question 7

In reliable transport protocols such as Transmission Control Protocol, what is the primary purpose of flow control between a sender and a receiver on a network connection?

Accepted Answer

Introduction / Context: This question checks your knowledge of one of the key functions of Transport layer protocols such as TCP, namely flow control. While transport protocols also handle error recovery and sometimes congestion control, flow control specifically focuses on preventing a fast sender from overwhelming a slower receiver, which is essential for stable and efficient communication between endpoints. Given Data / Assumptions: - We are dealing with reliable Transport layer protocols such as TCP rather than simple datagram protocols. - There is a sender and a receiver exchanging data over a network connection. - The question refers specifically to the purpose of flow control, not error control or encryption. - Mechanisms such as window sizes and acknowledgments are in play at this layer. Concept / Approach: Flow control is a mechanism that allows the receiver to advertise how much data it can buffer and process at any given time. In TCP this is typically implemented via the receive window field, which the receiver updates in acknowledgments to tell the sender how much additional data it may send without causing buffer overflow. The sender adjusts its sending rate accordingly. Flow control thus prevents packet loss and excessive retransmissions that would occur if the receiver were swamped with more data than it can handle. Step-by-Step Solution: Step 1: Separate the roles of various Transport layer functions: error control, flow control, and sometimes congestion control.Step 2: Recognize that error control deals with detecting and retransmitting lost or corrupted segments, while flow control deals with matching the sender rate to the receiver capacity.Step 3: Recall that TCP flow control uses a sliding window mechanism in which the receiver advertises a window size.Step 4: Understand that the sender uses this advertised window to determine how much unacknowledged data it may have in flight at any time.Step 5: Conclude that the primary purpose of flow control is to give the receiver the ability to govern how much data the sender transmits. Verification / Alternative check: You can verify this by thinking about what happens when the receiver application is slow or temporarily blocked. The TCP stack on the receiver will reduce the advertised window size, eventually to zero if necessary, which forces the sender to pause. When the application consumes data and buffer space becomes available, the receiver increases the window and the sender resumes transmission. This behavior is exactly what flow control is designed to provide. Why Other Options Are Wrong: Retransmitting data when acknowledgments are missing is part of error recovery and reliability, not specifically flow control. Reassembling segments in the correct sequence is also a Transport layer function but falls under ordered delivery rather than flow control. Regulating the size of each segment is related to maximum segment size negotiation and path MTU, again distinct from managing the sender rate. Encryption of segments is a security function and is not provided by flow control mechanisms. Common Pitfalls: Students often mix up flow control and congestion control. While both influence the sender rate, congestion control addresses conditions inside the network path such as queue buildup, whereas flow control protects the receiving endpoint. Mixing these concepts can lead to incorrect answers. Another pitfall is to assume that any reliability feature in TCP is part of flow control, when in fact reliability is a broader goal accomplished by several distinct mechanisms. Final Answer: The main purpose of flow control is to provide a means for the receiver to control how much data the sender transmits so that the receiver is not overwhelmed.

Question 8

Consider the following 32 bit binary value representing an IPv4 address in dotted binary notation 11001100.00110011.10101010.01010101. What is the equivalent dotted decimal IP address for this binary value?

Accepted Answer

Introduction / Context: This question assesses your ability to convert an IPv4 address written in dotted binary notation into the more familiar dotted decimal format. Being comfortable with binary to decimal conversion for octets is important for subnetting, interpreting network masks, and troubleshooting IP addressing problems in real world networks. Given Data / Assumptions: - The IPv4 address is given as four groups of eight bits separated by dots: 11001100.00110011.10101010.01010101. - Each group of eight bits represents one octet of the IPv4 address. - We need to convert each binary octet into its decimal value using base 2 positional weights. - No special subnetting or mask information is required beyond the conversion itself. Concept / Approach: An IPv4 address consists of four octets, each ranging from 0 to 255 in decimal. Each octet is an 8 bit binary number with bit weights 128, 64, 32, 16, 8, 4, 2, and 1 from left to right. To convert from binary to decimal, you add the weights corresponding to bit positions that are set to 1. You perform this operation separately for each octet and then join the resulting decimal values with dots to form the dotted decimal notation. Step-by-Step Solution: Step 1: Take the first octet 11001100. The bits set to 1 are at positions 128, 64, 8, and 4. Add them to get 128 + 64 + 8 + 4 which equals 204.Step 2: Take the second octet 00110011. The bits set to 1 are at positions 32, 16, 2, and 1. Add them to get 32 + 16 + 2 + 1 which equals 51.Step 3: Take the third octet 10101010. The bits set to 1 are at positions 128, 32, 8, and 2. Add them to get 128 + 32 + 8 + 2 which equals 170.Step 4: Take the fourth octet 01010101. The bits set to 1 are at positions 64, 16, 4, and 1. Add them to get 64 + 16 + 4 + 1 which equals 85.Step 5: Combine the four decimal octets to form the dotted decimal address 204.51.170.85. Verification / Alternative check: You can verify the conversion by reversing the process for one of the octets. For example, take decimal 204. Subtract 128 to get 76, subtract 64 to get 12, subtract 8 to get 4, subtract 4 to get 0. The remaining zero confirms that 204 is represented by bits 128, 64, 8, and 4 all set to 1, which corresponds to the binary pattern 11001100. Performing similar checks for the other octets confirms the correctness of the calculation. Why Other Options Are Wrong: 192.51.160.85 is incorrect because the first octet would require a different binary pattern, and 160 instead of 170 in the third octet shows a miscalculation. The values 204.19.170.85 and 204.51.168.95 contain incorrect decimal conversions of one or more octets, indicating wrong combinations of bit weights. The option 204.83.170.85 misrepresents the second octet and does not match the binary representation given. Common Pitfalls: Candidates often make mistakes by misplacing bit weights, especially confusing 32 and 64 or 8 and 16. Another error is to try to convert all 32 bits at once instead of treating each octet independently. Practicing with a simple table of powers of two and marking which bits are set helps reduce these errors and speeds up exam calculations. Final Answer: The binary IP address 11001100.00110011.10101010.01010101 corresponds to the dotted decimal address 204.51.170.85.

Question 9

In Cisco terminology a default Frame Relay wide area network is considered what type of physical network in terms of broadcast capability and multiaccess behavior?

Accepted Answer

Introduction / Context: This question tests your understanding of how Frame Relay wide area networks are classified from the perspective of routing and broadcast behavior. Knowing that Frame Relay is typically treated as a non broadcast multiaccess environment affects how you configure routing protocols, neighbor relationships, and mapping statements on interfaces that participate in a Frame Relay cloud. Given Data / Assumptions: - We are considering a default Frame Relay WAN rather than a special fully meshed design with extra features. - Multiple routers can be connected through a single Frame Relay cloud using permanent virtual circuits. - The network does not support native Layer 3 broadcast in the same way that Ethernet does. - The question asks for a classification in terms of broadcast versus non broadcast and multiaccess characteristics. Concept / Approach: A non broadcast multiaccess network is one in which many devices can reach one another at Layer 3, but the underlying technology does not support automatic broadcast or multicast at that same layer. Instead, you often have logical point to point or point to multipoint connections built on top of a shared infrastructure. Frame Relay has this property because it uses virtual circuits identified by DLCIs rather than shared broadcast domains, so routing protocols cannot simply rely on multicast to discover neighbors. Step-by-Step Solution: Step 1: Recognize that Frame Relay allows multiple routers to share a single physical access link to a cloud of connections, which satisfies the multiaccess part of the definition.Step 2: Understand that Frame Relay does not support generic broadcast or multicast for all attached routers in the same way as Ethernet, hence it is non broadcast by default.Step 3: Combine these properties to see that the correct classification is non broadcast multiaccess, often abbreviated NBMA.Step 4: Recall that many routing protocols such as OSPF and EIGRP require special configuration on NBMA networks to establish neighbor relationships.Step 5: Select the option that explicitly states non broadcast multiaccess network. Verification / Alternative check: You can verify this classification by recalling that when configuring OSPF over Frame Relay, you must often set the network type to non broadcast or point to multipoint and manually define neighbors. This is because the Frame Relay cloud does not provide a built in broadcast mechanism for OSPF hello packets. This practical configuration detail is a strong indicator that the network type is indeed NBMA. Why Other Options Are Wrong: Broadcast point to multipoint and broadcast multiaccess networks imply that the medium can flood broadcast packets to all attached devices, which is not true of standard Frame Relay. Non broadcast multipoint network is not the standard terminology used in Cisco material and does not emphasize the multiaccess nature as clearly as NBMA. A point to point leased line network only connects two sites directly and does not describe the multiaccess cloud characteristic of Frame Relay. Common Pitfalls: Students sometimes assume that because many Frame Relay deployments effectively behave like multiple point to point links, the underlying technology must be point to point. In reality, the physical interface can support multiple virtual circuits and is therefore treated as a multiaccess medium. Another pitfall is to confuse broadcast capability with the use of Inverse ARP or mapping commands, which do not change the fundamental non broadcast behavior. Final Answer: A default Frame Relay WAN is classified as a non broadcast multiaccess NBMA network.

Question 10

Which statement correctly describes a characteristic of IPv6 unicast addressing?

Accepted Answer

Introduction / Context: This question examines your understanding of IPv6 addressing rules, focusing specifically on unicast address ranges. Knowing how to recognize global unicast, link local, and multicast prefixes is essential for designing, configuring, and troubleshooting IPv6 networks. Many exam questions present several plausible looking prefixes, so you must be able to distinguish the correct ones from distractors. Given Data / Assumptions: - We are concerned with IPv6 unicast addressing, which identifies a single interface on a network. - One option references global unicast addresses starting at 2000::/3. - Other options mention link local prefixes and loopback or multicast semantics. - Only one statement must be correct, and the rest must contain inaccuracies about IPv6 addressing ranges or usage. Concept / Approach: In IPv6, global unicast addresses that are routable on the public Internet are commonly assigned from the 2000::/3 block, which covers addresses from 2000:: up to 3FFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF:FFFF. Link local addresses, which are used only on a single link for neighbor discovery and similar tasks, are assigned from FE80::/10. Multicast addresses start with FF00::/8. The loopback address is ::1, not the all zero address. Any statement that deviates from these facts is incorrect. Step-by-Step Solution: Step 1: Recall that global unicast addresses use the 2000::/3 range, so any statement that matches this is likely to be correct.Step 2: Remember that link local addresses start with FE80::/10, not FF00::/10 or FE00::/12.Step 3: Verify that the unique loopback address is ::1, which is a single address and not expressed as 0000::0 in typical notation.Step 4: Recognize that multicast addresses start with FF00::/8, not FE80::/10.Step 5: Based on these facts, identify the statement about global unicast addresses using the 2000::/3 prefix as the only correct choice. Verification / Alternative check: You can cross check the ranges by recalling how IPv6 addressing is often taught. Global unicast is described as IPv6 equivalent of public IPv4 addresses and diagrams usually show 2000::/3 with a variety of current allocations inside. Link local addresses always begin with FE80 and are automatically configured on interfaces. Multicast examples such as FF02::1 and FF02::2 clearly show the FF prefix. The loopback address ::1 appears frequently in examples and documentation and is easy to remember as the IPv6 counterpart of 127.0.0.1. Why Other Options Are Wrong: The claim that link local addresses start with FF00::/10 is wrong because that range is reserved for multicast, not unicast. Saying that link local addresses start with FE00::/12 is also incorrect because the used subset is specifically FE80::/10. The statement that the loopback address is 0000::0 is wrong because the loopback is ::1. Finally, the assertion that multicast addresses start with FE80::/10 confuses link local addressing with multicast addressing. Common Pitfalls: Students frequently confuse the FE80::/10 link local prefix with global unicast or multicast addresses because all three share the hex digit F. Another common error is to mix up the various sparse allocations that IPv6 documentation uses for examples. Memorizing the main ranges 2000::/3 for global unicast, FE80::/10 for link local, FF00::/8 for multicast, and ::1 for loopback helps avoid these mistakes in both exams and practice. Final Answer: The correct statement is that global unicast IPv6 addresses are allocated from the 2000::/3 prefix block.

Question 11

On a medium sized enterprise network you want to implement a mechanism that automatically assigns clients their IP address, subnet mask, default gateway, and DNS server information whenever they join the network. Which protocol is specifically desig…

Accepted Answer

Introduction / Context: This question addresses the need for automated IP configuration in modern networks. Manually assigning addresses to every workstation does not scale and leads to configuration errors. Instead, a dedicated protocol is commonly used to hand out IP related parameters to clients when they boot or join the network, greatly simplifying administration. Given Data / Assumptions: - The network has many client devices that require IP addresses and related configuration. - The administrator wants to automate assignment of IP address, subnet mask, default gateway, and DNS information. - The solution needs to be a standard protocol that clients and servers can implement. - Several protocols are listed, including some that serve unrelated purposes such as email or file transfer. Concept / Approach: Dynamic Host Configuration Protocol, or DHCP, is the standard protocol used to automatically assign IP configuration to clients. When a client boots, it broadcasts a discovery message. A DHCP server responds with an offer that includes an IP address lease and other options such as the subnet mask, default gateway, and DNS server addresses. The client requests and then receives this configuration with minimal manual intervention. None of the other listed protocols provide this comprehensive automatic configuration service. Step-by-Step Solution: Step 1: Eliminate protocols that obviously serve different purposes, such as SMTP for email, SNMP for management, and FTP for file transfers.Step 2: Consider ARP, which is used on local networks to map IP addresses to MAC addresses, but not to assign IP parameters.Step 3: Recall that DHCP was specifically created as an extension and evolution of earlier BOOTP mechanisms to dynamically configure IP hosts.Step 4: Note that DHCP can provide not only addresses but also many additional options such as DNS servers and domain names.Step 5: Select Dynamic Host Configuration Protocol DHCP as the correct answer. Verification / Alternative check: In practical network administration, configuring a DHCP server is a standard step when setting up a new subnet. Clients are normally set to obtain an IP address automatically. When they join the network, they receive all needed parameters without manual configuration. This real world workflow matches the description given in the question and confirms that DHCP is the protocol being referenced. Why Other Options Are Wrong: SMTP is a mail transfer protocol used to send email between servers and does not configure client addressing. SNMP is used for monitoring and managing network devices, not for assigning IP configuration. ARP resolves IP addresses to MAC addresses on the local segment and operates at a lower level than address assignment. FTP provides a mechanism to transfer files and does not have any role in dynamic host configuration. Common Pitfalls: Some learners may confuse DHCP with DNS because both appear in IP configuration dialogs. It is important to remember that DHCP distributes configuration information, while DNS resolves hostnames to IP addresses. Another pitfall is to think of ARP as a configuration protocol because it deals with addresses, but ARP is only concerned with mapping existing IP addresses to link layer identifiers, not with assigning those addresses in the first place. Final Answer: The Dynamic Host Configuration Protocol DHCP is the protocol used to automatically assign IP address, subnet mask, default gateway, and DNS information to clients.

Question 12

On a Cisco router running in ROM monitor mode you issue the command confreg 0x2142. What effect does this configuration register value have the next time the router is reloaded?

Accepted Answer

Introduction / Context: This operational question focuses on the Cisco configuration register and how it can be used during password recovery and troubleshooting. The confreg command is issued in ROM monitor mode to change how the router behaves when it boots. Understanding the meaning of common configuration register values such as 0x2102 and 0x2142 is essential for field engineers. Given Data / Assumptions: - The router is in ROM monitor mode, where low level commands such as confreg are available. - The administrator sets the configuration register to 0x2142. - The question asks what happens on the next reload after this register value is set. - We assume that there is a valid startup configuration stored in NVRAM before the change. Concept / Approach: The configuration register controls various boot time behaviors, including where to look for the startup configuration. The default value is typically 0x2102, which instructs the router to load the IOS image from Flash and then read the startup configuration from NVRAM. Changing the value to 0x2142 sets a specific bit that tells the router to ignore the startup configuration in NVRAM during the next boot. This behavior is especially useful for password recovery because it allows the router to come up with a clean configuration while preserving the original startup configuration file. Step-by-Step Solution: Step 1: Recall that 0x2102 is the default configuration register that loads both the IOS and the startup configuration.Step 2: Understand that 0x2142 modifies the behavior so that the router still loads the IOS image but skips applying the startup configuration.Step 3: Recognize that when the router boots with 0x2142, it will enter the initial configuration dialog or user mode with no existing configuration active.Step 4: The original startup configuration remains in NVRAM and can be copied into the running configuration later as part of password recovery.Step 5: Conclude that the main effect is to bypass the startup configuration during boot. Verification / Alternative check: In the standard Cisco password recovery procedure, one of the documented steps is to change the configuration register to 0x2142, reload the router, and then later copy startup config to running config after setting a new password. This documented workflow confirms that the purpose of 0x2142 is to ignore NVRAM startup configuration during the boot process rather than perform a full reset or clear flash memory. Why Other Options Are Wrong: Simply restarting the router is not unique to 0x2142 and does not describe the particular effect of this value. Forcing the router to boot into ROM monitor mode every time is associated with different configuration register bits, not with 0x2142. Displaying the enable secret password on the console is not performed by confreg; Cisco devices do not reveal this information directly. Clearing flash and reloading the IOS image is a destructive operation unrelated to the configuration register value in question. Common Pitfalls: A common mistake is to believe that 0x2142 erases the startup configuration, which is not true; it merely instructs the router to ignore it during boot. If engineers misunderstand this, they may fear losing configurations during password recovery when the configuration actually remains safe in NVRAM. Another pitfall is confusing different register values and forgetting to return the register to 0x2102 at the end of the recovery process, which can cause future boots to ignore configuration unexpectedly. Final Answer: Setting the configuration register to 0x2142 causes the router to ignore the startup configuration in NVRAM during the next boot so that existing settings can be bypassed.

Question 13

In an access layer switch design you have an interface that connects only to a single server and you want spanning tree to move that port to the forwarding state immediately without the usual listening and learning delays. Which Cisco IOS command sh…

Accepted Answer

Introduction / Context: This question deals with Spanning Tree Protocol configuration on Cisco switches, specifically in the context of access ports that connect only to end devices such as servers or workstations. While spanning tree is important for preventing loops, waiting through the full listening and learning states can delay link availability. Cisco provides a feature called PortFast to accelerate port transition for edge connections that are not expected to form loops. Given Data / Assumptions: - The port in question connects directly to a single server and is not part of any physical switching loop. - The goal is to bypass the normal spanning tree listening and learning delays on that interface so that it rapidly enters the forwarding state. - The underlying spanning tree topology should still run in the rest of the network. - We are looking for the Cisco IOS interface command that enables this behavior. Concept / Approach: On Cisco switches, the spanning-tree portfast command is used on access ports to allow them to transition quickly to the forwarding state. PortFast is intended only for ports connected to end hosts, not for trunk links between switches, because enabling it on links that can form loops can cause network instability. PortFast does not completely disable spanning tree; rather, it changes how the port behaves during startup, making it ideal for server or workstation connections. Step-by-Step Solution: Step 1: Identify that an access port connected to a single server is a typical candidate for PortFast.Step 2: Recall that the Cisco IOS command to enable this feature on an interface is spanning-tree portfast.Step 3: Understand that this command is applied in interface configuration mode, not in global configuration mode.Step 4: Recognize that the other listed commands either do not exist, are incomplete, or would disable spanning tree inappropriately.Step 5: Choose spanning-tree portfast as the correct answer. Verification / Alternative check: In practice, administrators often see messages on the console when enabling PortFast, warning that it should be used only on ports connected to a single host. When a device is plugged in, the port quickly transitions to forwarding, reducing issues such as delayed Dynamic Host Configuration Protocol assignment. This real world behavior aligns exactly with the description in the question. Why Other Options Are Wrong: The options disable spanning tree and spanning tree off are not valid Cisco IOS commands and, even if they existed, would be dangerous if they globally disabled spanning tree. The command spanning tree security does not represent a real feature in this syntax. The configuration no spanning tree vlan 1 would attempt to disable spanning tree for a particular VLAN rather than speeding up port activation, which is not the requirement here. Common Pitfalls: One common pitfall is to misunderstand PortFast as disabling spanning tree entirely on the port. In reality, spanning tree still runs and can block the port if a loop is detected. Another mistake is to enable PortFast on trunk ports between switches, which can lead to serious loop problems. Always reserve PortFast for access ports that are expected to connect only to end hosts. Final Answer: The correct interface command is spanning-tree portfast, which causes the server facing port to transition immediately to the forwarding state.

Question 14

Which of the following terms best describes the creation of private virtual networks across a shared public Internet infrastructure, providing privacy through encryption and allowing the tunneling of non IP or legacy protocols inside secure connecti…

Accepted Answer

Introduction / Context: This question addresses the high level concept of building private communications over a shared public network such as the Internet. Organizations frequently need to connect remote offices and users securely without deploying dedicated leased lines everywhere. To do this they use technologies that create private tunnels over a public infrastructure so that traffic remains confidential and sometimes can carry non native protocols. Given Data / Assumptions: - The public underlying network is IP based, for example the global Internet. - The solution must create private networks across this shared infrastructure. - The mechanism should provide privacy, usually via encryption, and support tunneling of additional protocols inside the secure channel. - Several technologies are listed, some of which relate to lower layer encapsulation or access methods rather than private overlay networks. Concept / Approach: The general term that describes creating a logically private network over a public infrastructure is Virtual Private Network or VPN. VPNs can be implemented using various underlying technologies, such as IPSec, Secure Sockets Layer, or Multiprotocol Label Switching, but the overarching idea remains the same: traffic is encapsulated and usually encrypted to form a private tunnel between sites or users. The question asks for this broad concept rather than any one implementation protocol. Step-by-Step Solution: Step 1: Identify keywords in the question such as private networks, across the Internet, privacy, and tunneling of non native protocols.Step 2: Recall that these terms collectively describe what VPN solutions provide to enterprises.Step 3: Recognize that IPSec is one common protocol suite used inside VPNs but is narrower in scope than the concept of a VPN itself.Step 4: Rule out other options such as HDLC, cable, and Frame Relay, which refer to link layer encapsulation or physical access methods rather than virtual overlays over the public Internet.Step 5: Select Virtual Private Network technology as the correct answer. Verification / Alternative check: In everyday networking language, engineers talk about setting up a site to site VPN tunnel between two branch offices or enabling remote access VPN for teleworkers. These phrases clearly match the description in the question. Although many of these deployments use IPSec under the hood, what the user experiences is a private virtual network connection riding on top of the public Internet, confirming that VPN is the correct general term. Why Other Options Are Wrong: HDLC is a data link layer protocol used for encapsulating network layer protocols over serial lines and does not in itself create private overlays across a public IP infrastructure. Cable refers to a broadband access medium that provides connectivity but not secure tunneling. IPSec is a protocol suite that can implement VPNs but is not the conceptual description requested here. Frame Relay PVCs are virtual circuits inside a provider network, not tunnels built across the open Internet. Common Pitfalls: One common pitfall is confusing a specific implementation, such as IPSec, with the broader concept of VPNs. Exams often distinguish between the conceptual term and the particular protocol used. Another mistake is to think that any dedicated service from a provider is automatically a VPN, even if it is simply a private leased line without tunneling or encryption over a public domain. Final Answer: The creation of private networks across the Internet with encrypted tunnels and protocol encapsulation is best described by the term Virtual Private Network VPN technology.

Question 15

In IP networking, how does the forwarding of a unicast IP packet differ from the forwarding of a multicast IP packet at a router?

Accepted Answer

Introduction / Context: This question compares how routers forward unicast IP packets versus multicast IP packets. Understanding this difference is fundamental for Cisco certification exams because unicast is the default forwarding model in most networks, while multicast uses special forwarding mechanisms and group-based addressing. Given Data / Assumptions: We are working in an IPv4 routed network that supports both unicast and multicast traffic. Routers maintain a unicast routing table (RIB and FIB) and, when multicast is enabled, a multicast routing table and group membership information. We are focusing on normal, correct operation, not on special tunneling or overlay techniques. Concept / Approach: Unicast forwarding is destination based: each packet has a single destination IP address, and the router looks up that address in its routing table to select a single next-hop and outgoing interface. Multicast forwarding is group based: the destination address represents a multicast group, and routers forward packets along a multicast distribution tree only on interfaces that lead to receivers that have joined that group, often using protocols such as IGMP and PIM plus reverse path forwarding checks. Step-by-Step Solution: Step 1: For a unicast packet, the router performs a longest-prefix match on the destination IP in the unicast routing table to find one best next-hop and one outgoing interface.Step 2: The router decrements the TTL, rewrites the Layer 2 header, and sends exactly one copy of the packet out that selected interface.Step 3: For a multicast packet, the router identifies the multicast group address (for example 239.x.x.x) and consults its multicast forwarding state to determine which outgoing interfaces are part of the multicast tree.Step 4: The router replicates the packet and sends a copy on each interface in the outgoing interface list, but only toward segments that have interested receivers or downstream routers.Step 5: Reverse path forwarding checks ensure that the multicast traffic is received on the correct incoming interface that matches the unicast route back to the source, helping to prevent loops. Verification / Alternative check: In a lab, you can observe unicast routing with commands such as show ip route and multicast forwarding state with show ip mroute. You will see that unicast entries map each prefix to a single next-hop, whereas multicast entries list an incoming interface and one or more outgoing interfaces, confirming the replication behavior. Why Other Options Are Wrong: Option B is incorrect because unicast traffic does not flood on all interfaces in a properly configured routed network, and multicast does not send a single copy only toward a default gateway.Option C is wrong because multicast traffic can and often does cross routers when multicast routing is enabled.Option D reverses concepts of source and destination trees and incorrectly claims there is no replication for multicast. Common Pitfalls: A common misconception is that multicast behaves like broadcast at Layer 3 and simply floods everywhere. In reality, multicast relies on explicit group membership and tree-building protocols, and routers forward multicast packets only where receivers exist. Another pitfall is thinking that unicast and multicast forwarding use the same routing table; multicast usually relies on additional multicast-specific state and sometimes on reverse path information derived from unicast routes. Final Answer: The key distinction is that Unicast forwarding sends one copy of the packet toward a single next-hop based on the destination IP, whereas multicast forwarding may replicate the packet out multiple interfaces along a multicast distribution tree toward all interested receivers in the group.

Question 16

In an OSPF network design, what is the primary purpose of using areas such as backbone area 0 and non-backbone areas?

Accepted Answer

Introduction / Context: This question is about the role of areas in an OSPF (Open Shortest Path First) network. OSPF is a link-state routing protocol, and its design includes the concept of areas such as the backbone area 0 and multiple non-backbone areas. Understanding why we divide an OSPF network into areas is a key objective in Cisco certification exams. Given Data / Assumptions: We are using OSPF as an interior gateway protocol inside a single autonomous system. The network may contain many routers and subnets, so scalability and stability are important. At least one backbone area (area 0) and one or more non-backbone areas can be created. Concept / Approach: OSPF is a link-state protocol, which means routers maintain a link-state database describing the topology of the entire area and run the SPF (Shortest Path First) algorithm to compute routes. In a single large area, every router would need to store and process LSAs for the entire network. By dividing the network into smaller areas and using area border routers (ABRs), OSPF reduces the size of each link-state database, limits the scope of LSA flooding, and contains topology changes within one area. This improves scalability and reduces CPU and memory load. Step-by-Step Solution: Step 1: Recognize that OSPF areas create a hierarchy: all non-backbone areas connect to area 0, which acts as the core.Step 2: Within each area, routers maintain a full link-state database and run SPF, but they do not store detailed topology information from other areas.Step 3: ABRs summarize and advertise inter-area routes so that routers learn reachability to other areas without full topology details.Step 4: Topology changes, link flaps, or LSA updates are mostly contained within the local area, limiting how far floods propagate.Step 5: Because each router only runs SPF on a reduced set of LSAs, convergence times and CPU usage are improved compared to a flat single-area design. Verification / Alternative check: When you compare a design with one large OSPF area to a design with multiple areas, you see that in the multi-area design, routers in a remote area do not receive every detailed LSA from other areas. Instead, they learn summarized inter-area routes, which clearly demonstrates how areas reduce database size and SPF workload. Why Other Options Are Wrong: Option B is incorrect because encryption and authentication in OSPF are independent of the concept of areas and are configured with additional security features.Option C is wrong because OSPF areas all use OSPF; you do not run different routing protocols in different OSPF areas.Option D is false because areas actually reduce the requirement for full mesh adjacencies; not all routers need to be neighbors. Common Pitfalls: A frequent misunderstanding is that areas are purely administrative or used only for policy. In reality, their key purpose is scalability and stability. Another pitfall is misconfiguring ABRs or failing to connect all non-backbone areas to area 0, which can break proper inter-area routing. Final Answer: The main reason to use areas is that To scale OSPF by reducing the size of each router's link-state database, limiting flooding, and minimizing SPF calculations through hierarchical design.

Question 17

In Cisco IOS show ip route output for OSPF, which list correctly represents the six common OSPF route types?

Accepted Answer

Introduction / Context: OSPF routes appear in the Cisco IOS show ip route output with specific codes that indicate the type of OSPF route. Knowing these codes is important for troubleshooting and for exams, because they reveal how a particular route entered the OSPF domain and how its metric is calculated. Given Data / Assumptions: We are focusing on Cisco IOS route table codes for OSPF, not on LSA type numbers. The question asks for six OSPF route types as seen in show ip route. Common OSPF route codes include O, O IA, O E1, O E2, O N1, and O N2, but Cisco often abbreviates these to O, O IA, E1, E2, N1, and N2 in explanations. Concept / Approach: Cisco categorizes OSPF learned routes in six main types: intra-area (O), inter-area (O IA), external type 1 (E1), external type 2 (E2), NSSA external type 1 (N1), and NSSA external type 2 (N2). Intra-area routes are learned within the same OSPF area; inter-area routes cross area boundaries via ABRs. External routes are redistributed from other routing domains into OSPF and are represented as E1 or E2 depending on how their cost is calculated. NSSA external routes (N1 and N2) are similar, but they originate from a Not-So-Stubby Area. Step-by-Step Solution: Step 1: Identify intra-area routes, marked with code O. These are routes that originate and stay within a single OSPF area.Step 2: Identify inter-area routes, marked with O IA, which are learned from another area via an ABR.Step 3: Recognize external routes of type 1, marked E1, where the external metric is added to the internal OSPF cost as the route crosses the OSPF domain.Step 4: Recognize external routes of type 2, marked E2, where only the external metric is considered and the internal OSPF cost is not added beyond the ASBR.Step 5: Identify NSSA external routes N1 and N2, which correspond to external type 1 and type 2 routes originated inside an NSSA, then translated and flooded into the rest of the OSPF domain. Verification / Alternative check: On a Cisco router, issuing show ip route ospf in a lab that includes multiple areas and redistribution from another protocol will display entries starting with O, O IA, O E1, O E2, O N1, and O N2. These six codes confirm the list described in option A. Why Other Options Are Wrong: Option B lists general route codes such as C and S that are not specific to OSPF.Option C repeats the O prefix unnecessarily and mentions an extra type for default routes, which is not a separate OSPF route type.Option D refers to IS-IS style L1 and L2 designations, which belong to a different routing protocol, not to OSPF. Common Pitfalls: Candidates sometimes confuse LSA types with route codes, or they assume that all external routes in OSPF look the same. Remember that the route table codes O, O IA, E1, E2, N1, and N2 provide a quick summary of where the route came from and how its metric is treated, which is critical during troubleshooting. Final Answer: The correct list is O, O IA, E1, E2, N1, N2 (intra-area, inter-area, external type 1, external type 2, NSSA external type 1, NSSA external type 2).

Question 18

In IPv4 networks, which UDP port numbers are reserved for the DHCP client and DHCP server?

Accepted Answer

Introduction / Context: Dynamic Host Configuration Protocol (DHCP) is widely used in IP networks to automatically assign IP addresses and other parameters to hosts. For Cisco and general networking exams, you must know the well-known port numbers associated with DHCP and whether the protocol uses UDP or TCP. Given Data / Assumptions: The question asks specifically about port numbers used by DHCP. We are in an IPv4 context, using the standard DHCP protocol defined over UDP. We want to identify which ports are reserved for the server and the client. Concept / Approach: DHCP uses UDP, not TCP, because DHCP messages are small, connectionless, and must work even before a host has a full IP configuration. By convention, the DHCP server listens on UDP port 67 and the DHCP client listens on UDP port 68. During discovery and offer, a client often uses a source port of 68 and a destination port of 67, and servers respond from port 67 back to port 68. Step-by-Step Solution: Step 1: Recall that DHCP is an extension of BOOTP and operates over UDP, not over TCP.Step 2: The server side of DHCP services must use a well-known port so that clients know where to send requests; this is UDP port 67.Step 3: The client uses UDP port 68 so that its DHCP process can receive replies from the server.Step 4: When a client sends a DHCPDISCOVER broadcast, it typically uses source port 68 and destination port 67.Step 5: The server replies with DHCPOFFER and other messages, using source port 67 and destination port 68, preserving the same mapping. Verification / Alternative check: On a router or firewall that can display session tables or packet captures, you can observe DHCP traffic. You will see UDP packets with source and destination ports 67 and 68, confirming the reserved ports for client and server roles. Why Other Options Are Wrong: Option B is wrong because the client does not use a random high port; it specifically uses UDP port 68.Option C incorrectly states that DHCP uses UDP port 69, which is reserved for TFTP, not for DHCP.Option D is incorrect because DHCP does not use TCP; reliable delivery is not guaranteed by the transport layer but is handled by retransmission logic in the DHCP protocol. Common Pitfalls: A common exam mistake is to confuse DHCP ports with other well-known ports such as TFTP (69) or to think that DHCP relies on TCP because it is an important control protocol. Memorizing that DHCP uses UDP 67 and 68 is an easy way to avoid this confusion. Final Answer: The correct statement is that UDP port 67 for the DHCP server and UDP port 68 for the DHCP client are reserved for DHCP.

Question 19

In network security, what is the primary function of a firewall placed between two networks such as a LAN and the Internet?

Accepted Answer

Introduction / Context: Firewalls are a core component of network security architectures. For Cisco and other networking certifications, you must understand what a firewall actually does, and also what it does not do by itself. This question asks for the primary function of a firewall deployed between two networks. Given Data / Assumptions: A firewall is positioned between an internal trusted network and an external or less trusted network such as the Internet. The firewall is configured with security policies that define which traffic is allowed or denied. The question focuses on the main purpose, not on every advanced capability. Concept / Approach: At its core, a firewall inspects network traffic at one or more layers (for example, packet filtering, stateful inspection, or application layer inspection) and enforces security policies. These policies are expressed as rules that match on IP addresses, ports, protocols, and sometimes application content. The firewall decides whether each packet or flow should be permitted, denied, or subject to additional processing such as NAT or logging. Step-by-Step Solution: Step 1: Understand that traffic moving between two networks passes through the firewall as an intermediate device.Step 2: The firewall examines packet headers and, in some cases, packet payloads to determine which rule applies.Step 3: Based on the configured policy, the firewall permits, drops, or rejects the traffic. It may also perform state tracking to ensure that packets belong to valid sessions.Step 4: The firewall can log decisions, apply NAT, and integrate with intrusion prevention systems, but these are additional capabilities built on top of the basic permit or deny function. Verification / Alternative check: On real firewalls, commands such as show access-list, show security policy, or logs from blocked connections demonstrate that the firewall is continuously matching traffic against rules and deciding whether to forward or block packets. This behaviour directly supports the description in option A. Why Other Options Are Wrong: Option B describes simple address mapping or NAT functionality without security filtering, which is not the primary role of a firewall.Option C reduces the firewall to a pure antivirus scanner based on signatures, which is more typical of an antivirus or IDS or IPS device.Option D exaggerates firewall capabilities; no firewall can guarantee complete virus prevention without other layers such as endpoint protection and user training. Common Pitfalls: Many newcomers think that a firewall alone can solve all security problems, including malware and phishing. In reality, a firewall enforces network access control policies but must be combined with other tools. Recognizing that its fundamental job is to examine traffic and decide what to allow or deny keeps expectations realistic and aligns with exam objectives. Final Answer: The primary function of a firewall is that It examines packets and applies security rules to decide which traffic should be allowed or denied between networks.

Question 20

In relation to the OSI model, which of the following devices does not operate at all seven layers but is instead focused mainly on the lower layers?

Accepted Answer

Introduction / Context: This question tests your understanding of how different network devices map to the OSI model layers. Some devices, like hosts and servers, implement protocol functionality all the way from the physical layer up to the application layer. Others, like routers, focus mainly on specific lower layers. Given Data / Assumptions: The OSI model has seven layers from Physical (Layer 1) to Application (Layer 7). Routers are classic Layer 3 devices that may have some awareness of Layer 2 and Layer 4, but do not implement full application layer functions for user traffic. Hosts, servers, and management stations typically run complete protocol stacks and applications. Concept / Approach: A network host, such as a PC, typically runs applications (Layer 7), presentation and session functions, transport protocols like TCP and UDP, network layer protocols such as IP, and data link and physical interfaces. Similarly, web or application servers and network management stations run processes at all layers. Routers, by contrast, are primarily concerned with examining Layer 3 headers, updating routing tables, and forwarding packets between networks. While modern routers may have limited features that inspect higher-layer information, they are not general application endpoints. Step-by-Step Solution: Step 1: Consider network hosts and servers. They must support user applications, perform encryption or presentation tasks, manage sessions, and handle full transport and network stacks.Step 2: Network management stations similarly run management applications and agents that interact with devices at many layers, including application protocols such as SNMP.Step 3: Routers connect different IP networks. Their primary job is to examine IP headers, make forwarding decisions, and possibly apply access control or QoS based on Layer 3 and sometimes Layer 4 information.Step 4: Because routers do not act as general application endpoints, they are not said to operate at all seven OSI layers in the same sense that hosts do. Verification / Alternative check: Looking at device roles: hosts use a browser to access web pages (Layer 7), while routers pass the HTTP packets between networks without acting as the HTTP application themselves. This demonstrates that routers are not operating as full Layer 7 devices for user traffic. Why Other Options Are Wrong: Option A is incorrect because network management stations run applications and full protocol stacks.Option C is wrong because web and application servers clearly operate at the application layer in addition to lower layers.Option D is incorrect because general network hosts participate in all layers from Physical to Application when they run end user software. Common Pitfalls: Some learners think that a router operates at every layer simply because it touches every packet. Remember that device classification is based on where the device makes decisions and ends or originates flows, not merely on where packets are visible in hardware. Final Answer: The device that does not operate at all OSI layers in the sense of a full endpoint is Routers that forward packets primarily based on Layer 3 addressing and routing protocols.

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