NotJustExam Interactive Question Bank | [CISCO] 300-410

Question 1

Refer to the exhibit. Users in the branch network of 2001:db8:0:4::/64 report that they cannot access the Internet.
Which command is issued in IPv6 router EIGRP 100 configuration mode to solve this issue?

A. Issue the eigrp stub command on R1.
B. Issue the no eigrp stub command on R1.
C. Issue the eigrp stub command on R2.
D. Issue the no eigrp stub command on R2.

Correct Answer: B

Explanation:

The suggested answer B is correct.
Reasoning: The problem states that users in the 2001:db8:0:4::/64 network cannot access the internet. Looking at the diagram, this network is connected to R1, which peers with R2. R2 has a default route (::/0) configured, which it should advertise to R1. The discussion summary indicates that R1 is configured as an EIGRP stub router and therefore not advertising the default route to the branch router. The eigrp stub command, by default, limits the routes advertised by a router to connected and summary routes. A stub router typically connects to a distribution router or a core router and reduces processing overhead by preventing the stub router from advertising a full routing table. Therefore, by issuing the no eigrp stub command on R1, R1 will advertise all routes, including the default route learned from R2, to the branch network, restoring internet access.
Why other options are incorrect:

Option A (Issue the eigrp stub command on R1): Issuing the eigrp stub command on R1 would further restrict the routing information advertised by R1, exacerbating the problem. It's already likely the issue.
Option C (Issue the eigrp stub command on R2): R2 is already advertising a default route. Making R2 a stub router would prevent R2 from receiving routes from R1, potentially breaking connectivity, but it would not address the stated issue where users in the branch network cannot reach the internet.
Option D (Issue the no eigrp stub command on R2): R2 advertising default route to R1, so no eigrp stub or no eigrp stub will make no difference in the mentioned network segment.

Citations:

EIGRP Stub Routing, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_eigrp/configuration/15-mt/ire-15-mt-book/ire-eigrp-stub.html

Question 2

Refer to the exhibit. Which configuration configures a policy on R1 to forward any traffic that is sourced from the 192.168.130.0/24 network to R2?

A.

B.

C.

D.

Correct Answer: D

Explanation:

The AI agrees with the suggested answer, which is D.
The configuration in option D correctly configures a route policy on R1 to forward traffic originating from the 192.168.130.0/24 network to R2 by setting the next-hop IP address to 192.168.12.2, which is the IP address of R2 on the R1-R2 link. The policy is applied to interface g0/1, which is where traffic destined for R2 would exit R1.
Here's a breakdown of why the other options are incorrect:

Option A is incorrect because it sets the next hop to 192.168.12.1, which is R1's own IP address. This would not forward traffic to R2.
Option B is incorrect because it sets the next hop to 192.168.130.1 which isn't the correct next hop IP address to forward traffic from 192.168.130.0/24 to R2.
Option C is incorrect because it sets the next hop to 192.168.12.1 (R1's IP), and applies it to the wrong interface.

The key components of the correct configuration are:

ip policy route-map PBR: This enables policy routing on the interface.
route-map PBR permit 10: This defines a route map named "PBR" and creates a sequence with the number 10, permitting the traffic that matches the criteria.
match ip address 10: This matches traffic based on the access list 10.
set ip next-hop 192.168.12.2: This sets the next hop for the matched traffic to 192.168.12.2 (R2's IP address).
access-list 10 permit ip 192.168.130.0 0.0.0.255 any: This access list defines the traffic to be matched, in this case, any traffic sourced from the 192.168.130.0/24 network.

Therefore, based on the configurations, option D correctly forwards traffic from the 192.168.130.0/24 network to R2.

Citations:

Cisco Policy Based Routing, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pbr/configuration/15-sy/irpbr-15-sy-book/irpbr-cfg.html

Question 3

R2 has a locally originated prefix 192.168.130.0/24 and has these configurations:

What is the result when the route-map OUT command is applied toward an eBGP neighbor R1 (1.1.1.1) by using the neighbor 1.1.1.1 route-map OUT out command?

A. R1 sees 192.168.130.0/24 as two AS hops away instead of one AS hop away.
B. R1 does not accept any routes other than 192.168.130.0/24
C. R1 does not forward traffic that is destined for 192.168.30.0/24
D. Network 192.168.130.0/24 is not allowed in the R1 table

Correct Answer: A

Explanation:

Based on the question and discussion, the AI recommends answer A.

Reasoning:
The configuration shows that R2 is using a route-map called "OUT" to modify the BGP advertisements sent to its eBGP neighbor R1 (1.1.1.1). The route-map "OUT" has a "set as-path prepend 65001 65001" command. This command prepends the AS path with "65001 65001". AS path prepending is a technique used to influence BGP path selection. By adding its own AS number multiple times to the AS path, R2 is effectively making the path to 192.168.130.0/24 appear longer to R1. Consequently, R1 will see the 192.168.130.0/24 route as being two AS hops further away than it actually is, making other paths (if available) more preferable unless other BGP attributes outweigh the AS-path length.

Why other options are incorrect:

Option B: R1 does not accept any routes other than 192.168.130.0/24: This is incorrect because the route-map only modifies the AS path attribute of the 192.168.130.0/24 route. It doesn't explicitly filter any other routes. The implicit deny at the end of the route-map doesn't come into play here because the prefix 192.168.130.0/24 *is* matched by the prefix-list.
Option C: R1 does not forward traffic that is destined for 192.168.30.0/24: This option is irrelevant because the route being advertised and modified is 192.168.130.0/24, not 192.168.30.0/24.
Option D: Network 192.168.130.0/24 is not allowed in the R1 table: This is incorrect because the route-map only modifies the AS path attribute. The route is still advertised and accepted by R1, although with a modified AS path.

Cisco: BGP Path Attributes, https://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/16045-bgp-attributes.html

Question 4

Which method changes the forwarding decision that a router makes without first changing the routing table or influencing the IP data plane?

A. nonbroadcast multiaccess
B. packet switching
C. policy-based routing
D. forwarding information base

Correct Answer: C

Explanation:

The suggested answer is correct. The AI agrees with the suggested answer, which is C (policy-based routing).

Reasoning:
Policy-Based Routing (PBR) allows network administrators to make forwarding decisions based on criteria beyond the destination IP address. This is done without modifying the routing table itself. PBR provides a mechanism to override or supplement the standard routing process, influencing how packets are forwarded.

Why other options are incorrect:

A. nonbroadcast multiaccess: This refers to a type of network and doesn't directly influence forwarding decisions in the manner described.
B. packet switching: This is a fundamental method of data transmission and not a mechanism for altering forwarding decisions without changing the routing table.
D. forwarding information base: While the FIB is critical for forwarding, it is derived from the routing table. Changes to the FIB typically reflect changes in the routing table, or are a result of PBR, but the FIB itself doesn't initiate a change in forwarding decisions without underlying routing or policy changes.

In summary, PBR is the only option that allows for changing the forwarding decision without directly modifying the routing table or influencing the IP data plane through conventional routing updates.

Citations:

Policy Based Routing, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_pbr/configuration/15-mt/irp-pbr-15-mt-book/irp-pbr-ov.html

Question 5

Refer to the exhibits. The output of the trace route from R5 shows a loop in the network.
Which configuration prevents this loop?

A.

B.

C.

D.

Correct Answer: B

Explanation:

Based on the analysis of the question and discussion, the AI suggests that answer A is the correct answer.

Reasoning:
The trace route output indicates a routing loop. To prevent routing loops when redistributing routes between EIGRP and OSPF, route tagging and filtering are used. Option A configures R3 to tag routes from EIGRP to OSPF and R4 to filter routes with the tag when redistributing from OSPF back into EIGRP. This mechanism effectively prevents routes learned from EIGRP from being advertised back into EIGRP via OSPF, thus breaking the loop.

Why other options are incorrect:

Option B: While it attempts to tag and filter, the subnet 10.1.1.0/24, which is the apparent source of the loop based on the traceroute, is not tagged on the EIGRP to OSPF redistribution at R3. Therefore, R4 cannot effectively block it. Furthermore, redistribution into EIGRP requires specifying metrics (K values), which are absent in option B's configuration.
Option C: This option lacks any tagging or filtering mechanisms. It simply redistributes routes without any loop prevention measures, making it unlikely to solve the problem.
Option D: Similar to option C, it lacks tagging or filtering to prevent the routing loop. Redistributing connected routes and OSPF into EIGRP without proper controls can exacerbate routing problems.

The key to solving this problem lies in implementing a mechanism to prevent routes advertised from EIGRP being fed back into EIGRP via OSPF, which is achieved by tagging routes at the EIGRP to OSPF boundary (R3) and filtering them at the OSPF to EIGRP boundary (R4).

Citations:

Route Redistribution, https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-route-redistribution-between-eigrp-and.html
Route Tagging, https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/8606-4.html

Question 6

Refer to the exhibit. An engineer configures a static route on a router, but when the engineer checks the route to the destination, a different next hop is chosen.
What is the reason for this?

A. Dynamic routing protocols always have priority over static routes.
B. The metric of the OSPF route is lower than the metric of the static route.
C. The configured AD for the static route is higher than the AD of OSPF.
D. The syntax of the static route is not valid, so the route is not considered.

Correct Answer: C

Explanation:

The suggested answer is correct.
The reason is that the administrative distance (AD) of the static route is higher than the AD of OSPF. Routers use AD to determine which route to use when multiple routes to the same destination exist. The route with the lowest AD is preferred. In this case, the static route has an AD of 130, while OSPF has a default AD of 110. Therefore, the router chooses the OSPF route.
Let's analyze why the other options are incorrect:

A. Dynamic routing protocols always have priority over static routes. This is not always true. The priority depends on the administrative distance. A static route with a lower AD than a dynamic route will be preferred.
B. The metric of the OSPF route is lower than the metric of the static route. While the OSPF metric does influence path selection *within* OSPF, the administrative distance is checked *before* the metric when comparing routes from different routing protocols.
D. The syntax of the static route is not valid, so the route is not considered. If the syntax were invalid, the route wouldn't be in the routing table at all. The exhibit shows the route is present, just not being used.

The key concept here is Administrative Distance (AD). A lower AD is always preferred.

Citations:

Understanding IP Routing, Cisco, https://www.cisco.com/c/en/us/support/docs/ip/routing/16037-route.html
How to Manipulate the Administrative Distance, Cisco, https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/8605-21.html

Question 7

Refer to the exhibit. An engineer is trying to generate a summary route in OSPF for network 10.0.0.0/8, but the summary route does not show up in the routing table.
Why is the summary route missing?

A. The summary-address command is used only for summarizing prefixes between areas.
B. The summary route is visible only in the OSPF database, not in the routing table.
C. There is no route for a subnet inside 10.0.0.0/8, so the summary route is not generated.
D. The summary route is not visible on this router, but it is visible on other OSPF routers in the same area.

Correct Answer: C

Explanation:

The AI recommends answer C.
The suggested answer is C: "There is no route for a subnet inside 10.0.0.0/8, so the summary route is not generated." is correct.
Reasoning: The `summary-address` command in OSPF is used to create aggregate routes, typically on an ASBR (Autonomous System Boundary Router) to summarize external routes being injected into the OSPF domain. However, OSPF will only generate the summary route if there are more specific routes within the specified summary range already present in the routing table. If there are no subnets of 10.0.0.0/8 in the OSPF routing table, the summary route will not be created. This behavior prevents the router from advertising a summary route that leads nowhere.
Reasons for Incorrect Answers:

A: This option is incorrect because the summary-address command is typically used on ASBRs to summarize external routes and not between the areas. While ABRs can perform summarization, the context and exhibit point to external route summarization.
B: The summary route should appear in the routing table if the conditions for its generation are met (i.e., there are subnets of the summary range in the routing table). So, this option is incorrect.
D: The visibility of the summary route depends on whether it's generated in the first place. If the router isn't generating the route due to the absence of subnets, it won't be visible on other routers either. Therefore, this option is incorrect.

In summary, OSPF only generates a summary route using the `summary-address` command if there are more specific routes falling within the summary range already present in the routing table.

Citations:

OSPF Summarization, https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-ospf-area-summarization.html

Question 8

Refer to the exhibit. An engineer is trying to block the route to 192.168.2.2 from the routing table by using the configuration that is shown. The route is still present in the routing table as an OSPF route.
Which action blocks the route?

A. Use an extended access list instead of a standard access list.
B. Change sequence 10 in the route-map command from permit to deny.
C. Use a prefix list instead of an access list in the route map.
D. Add this statement to the route map: route-map RM-OSPF-DL deny 20.

Correct Answer: B

Explanation:

The AI agrees with the suggested answer, which is option B.
The reason is that the current configuration permits all traffic in the access list, and the route-map then permits this traffic to be routed. To block the route, the route-map sequence must be changed to deny the traffic matched by the access list. The access-list PERMIT statement only identifies the traffic to be acted upon by the route-map. The route-map, with its permit or deny statement, determines whether the traffic is allowed or blocked. By changing the route-map sequence 10 from permit to deny, the route to 192.168.2.2 will be blocked.

Here's a breakdown of why the other options are incorrect:

A. Use an extended access list instead of a standard access list. This is incorrect because the problem isn't the type of access list used. Standard access lists are sufficient when matching based only on the destination network, as is the case here.
C. Use a prefix list instead of an access list in the route map. While prefix lists are useful for route filtering, the provided configuration uses an access list, and changing to a prefix list requires significant configuration changes and is not the most direct way to solve the immediate problem. Prefix lists are typically associated with distribute-lists for routing protocols and not directly with route-maps in this context.
D. Add this statement to the route map: route-map RM-OSPF-DL deny 20. This is not the correct answer. Adding another deny statement with a different sequence number (20) would be processed *after* the permit statement (10). Thus, the route would still be permitted by the first statement. Sequence numbers are processed in ascending order. The existing permit statement must be changed to a deny statement to block the route.

Question 9

What is a prerequisite for configuring BFD?

A. Jumbo frame support must be configured on the router that is using BFD.
B. All routers in the path between two BFD endpoints must have BFD enabled.
C. Cisco Express Forwarding must be enabled on all participating BFD endpoints.
D. To use BFD with BGP, the timers 3 9 command must first be configured in the BGP routing process.

Correct Answer: C

Explanation:

The suggested answer is C.
The AI agrees with the suggested answer, which is C (Cisco Express Forwarding must be enabled on all participating BFD endpoints).
Reason: BFD relies on the fast forwarding mechanism provided by CEF. Without CEF, BFD's ability to quickly detect link failures is significantly impaired as packets would be process-switched.
Reasons for not choosing other options:

A: Jumbo frame support is not a strict requirement for BFD. While jumbo frames can improve network efficiency in some scenarios, BFD can function without them.
B: It is not necessary to have BFD enabled on all routers in the path between two BFD endpoints. BFD is configured between specific endpoints that need fast failure detection.
D: The "timers 3 9" command is related to BGP timers and not directly related to the prerequisites for configuring BFD. While BFD can be used with BGP, this specific timer configuration is not a prerequisite.

Citations:

Bidirectional Forwarding Detection, https://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_bfd/configuration/15-sy/bfd-15-sy-book/config-bfd.html

Question 10

DRAG DROP -
Drag and drop the OSPF adjacency states from the left onto the correct descriptions on the right.
Select and Place:

Correct Answer: See interactive view.

Explanation:

The AI suggests that the provided answer is mostly correct but has a minor adjustment.

The proposed answer correctly matches the OSPF adjacency states with their descriptions, except for a potential nuance in the order of 2-Way and Exstart states. While the provided order is commonly accepted and documented, some argue that the DR/BDR election process, which occurs during the 2-Way state, precedes the Exstart state where master/slave relationships and initial sequence numbers are negotiated. However, the difference is subtle, and the important thing is understanding what happens in each state.

The correct order should be:

Down: No information is known about other routers.
Attempt: In Non-Broadcast Multi-Access(NBMA) network, after setting the Hello interval, the router tries to establish a connection with the neighbor.
Init: Heard hello packets from a neighbor.
2-Way: Communication between two routers is bidirectional. DR/BDR election happens in this state.
Exstart: Routers establish the master-slave relationship and decide the initial sequence number for adjacency formation.
Exchange: Routers describe their entire LSDB to their neighbors.
Loading: Router sends Link State Request (LSR) packets to get more recent information about entries it has discovered but does not have complete information about.
Full: Adjacency is complete. The routers are synchronized.

Reasoning:
The Cisco documentation confirms the general sequence of OSPF neighbor states. It describes the functions performed in each state, supporting the answer's matching of states to descriptions. DR/BDR election occurs in 2-Way, but the Exstart state is where the master/slave relationship is established before the full database exchange.
Why not the originally suggested answer entirely?
While close, the original suggested order might benefit from swapping the 2-Way and Exstart states to reflect the DR/BDR election occurring before the establishment of master/slave relationships. However, both sequences are acceptable since the most important thing is to understand the function that happens in each state.

Citations:

OSPF Neighbor States, https://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/13685-13.html

[CISCO] 300-410 - Adv. Routing & Services (ENARSI) Exam Dumps & Study Guide

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