JN0-106 Routing Fundamentals Practice Test 4 — 15 Questions

Question 1

An administrator wants to drop traffic destined to the 10.10.10.0/24 network without sending an ICMP unreachable message back to the source. Which static route option should be used?

Accepted Answer

discard. The 'discard' static route option silently drops traffic destined to the 10.10.10.0/24 network without generating any ICMP unreachable message. This is in contrast to the 'reject' option, which drops traffic but sends an ICMP unreachable back to the source. The 'discard' route is ideal for blackholing unwanted traffic while avoiding unnecessary network feedback.

Answer

reject

Answer

next-table

Answer

resolve

Question 2

Which two factors does Junos use to select the best route when multiple routes to the same prefix exist? (Choose two.)

Accepted Answer

Route preference. Junos uses route preference as the first tie-breaker when multiple routes to the same prefix exist. If route preference is equal, then metric (also known as cost) is compared. Next-hop type, number of hops, and route age are not standard factors used in the route selection process for JNCIA. Therefore, the correct answers are A (Route preference) and D (Metric).

Answer

Next-hop type

Answer

Number of hops

Answer

Route age

Question 3

Which two static route options result in traffic being dropped at the router? (Choose two.)

Accepted Answer

reject. (reject) is correct because a static route with the 'reject' attribute causes the router to drop packets destined for that prefix and send an ICMP unreachable message back to the source. Option D (discard) is correct because it silently drops packets without sending any ICMP notification. Both effectively result in traffic being dropped at the router.

Answer

install

Answer

next-table

Answer

resolve

Question 4

Which three characteristics are true for OSPF? (Choose three.)

Accepted Answer

Supports VLSM (Variable Length Subnet Masks). OSPF is a link-state routing protocol that supports Variable Length Subnet Masks (VLSM), which allows it to advertise subnets of different sizes within the same major network. This is a key advantage over classful protocols like RIPv1, as OSPF includes the subnet mask in its Link-State Advertisements (LSAs), enabling efficient IP address utilization.

Answer

Uses the Bellman-Ford algorithm

Answer

Is classful and does not support VLSM

Question 5

Refer to the exhibit. Why is the route via 10.0.0.1 selected as the active route?

Accepted Answer

It has a lower preference. In Junos, the active route is selected based on the route preference value, where a lower preference is preferred. Since the route via 10.0.0.1 has a lower preference than the other route, it is chosen as active. This is a fundamental Junos routing decision process, distinct from metrics which are used within a single routing protocol.

Answer

It has a lower metric

Answer

It has a lower cost

Answer

It is an older route

Question 6

A network engineer is managing a hub-and-spoke OSPF network for a retail company. The hub router (hub01) is at the data center with a loopback address 10.99.99.99. The spoke router (spoke01) is at a branch office and connects to hub01 via two links: a primary T1 link on interface ge-0/0/0.0 and a backup LTE link on interface lte-0/0/0.0. Both links are in area 0. Recently, the spoke router began sending traffic to the hub's loopback over the LTE link instead of the T1 link, causing higher latency and data charges. The engineer checks the routing table on spoke01 and sees that the route to 10.99.99.99/32 has two equal-cost next-hops: one via ge-0/0/0.0 and one via lte-0/0/0.0. The engineer wants to ensure that only the T1 link is used under normal conditions, with the LTE link as a backup. Which action should the engineer take to achieve this?

Accepted Answer

Increase the OSPF cost on interface lte-0/0/0.0 to a value higher than the cost on ge-0/0/0.0.. By increasing the OSPF cost on the LTE interface (lte-0/0/0.0) to a value higher than the cost on the T1 interface (ge-0/0/0.0), OSPF will prefer the lower-cost path via ge-0/0/0.0, breaking the equal-cost multipath (ECMP) and making the T1 path the active route. The LTE path remains as a backup if the T1 link fails. Option A (decreasing cost on ge-0/0/0.0 to 1) might already be at minimum and would not help if costs are equal; also, lowering cost could make it even more preferred, but the issue is equal cost, so increasing cost on the undesired path is more straightforward. Option B (static route with lower preference) would override OSPF, but it is not necessary and could lead to administrative overhead. Option C (OSPF priority) affects DR/BDR election, not route selection to external destinations. Therefore, D is the correct action.

Answer

Decrease the OSPF cost on interface ge-0/0/0.0 to 1.

Answer

Configure a static route to 10.99.99.99/32 with next-hop referencing the T1 interface and a lower preference than OSPF.

Answer

Set the OSPF priority on ge-0/0/0.0 to 128 to influence the designated router election.

Question 7

A service provider operates a Juniper MX router that receives a default route from two different ISPs via EBGP. Both ISPs advertise 0.0.0.0/0 with the same local preference (100), same AS path length, and same metric. The network administrator wants to load balance outgoing traffic across both ISPs for redundancy and bandwidth utilization. After applying the configuration, the administrator checks the routing table and sees that only one default route is active, the one from ISP-A. The other route from ISP-B is present but not active. The administrator verifies that both routes have the same preference (170) and same BGP attributes. The ISP links are different: ISP-A is connected via interface ge-0/0/0.0 with next-hop 10.1.1.2, and ISP-B via interface ge-0/0/1.0 with next-hop 10.2.2.2. What is the most likely reason that both routes are not active and load-balanced?

Accepted Answer

The BGP routes are from different autonomous systems.. By default, Junos BGP does not load balance routes from different autonomous systems. To enable multipath across different ASes, the 'multipath multiple-as' command must be configured under BGP. Option A is irrelevant. Option B is not a cause because different next-hops can be load-balanced under multipath. Option D is the solution, not the cause. Therefore, the most likely cause is that the routes are from different ASes.

Answer

The router has 'no-policy-statistics' enabled on the BGP sessions.

Answer

The BGP routes have different next-hop addresses.

Answer

The router is configured with 'multipath multiple-as' under BGP.

Question 8

A network engineer is troubleshooting a connectivity issue between two directly connected routers, R1 and R2. Both routers have IP addresses configured on their respective interfaces, and the interfaces are up. However, 'ping 192.168.1.2 source 192.168.1.1' from R1 fails. The engineer checks the routing table on R1 and sees a static route to 0.0.0.0/0 via a different next-hop, but no route for the 192.168.1.0/24 network. What is the most likely cause?

Accepted Answer

The route to the directly connected network is missing from the routing table, possibly because the interface is not properly configured or the link is down.. In Junos, a directly connected route is installed in the routing table only when the interface is operationally up and has a valid IP configuration. If no route for 192.168.1.0/24 exists, the interface is not operationally up (e.g., no carrier) or the IP configuration is incorrect, even if the interface shows as administratively up. Therefore, the missing route is the symptom, and the underlying cause is an interface that is not fully operational or is misconfigured.

Answer

The ARP cache is stale and needs to be cleared.

Answer

The interface is not configured with an IP address.

Answer

A security policy is blocking ICMP traffic between the two routers.

Question 9

Which TWO statements about static routes in Junos OS are correct? (Choose two.)

Accepted Answer

A static route can have a next-hop specified as an interface name for point-to-point interfaces.. In Junos OS, a static route can specify a next-hop as an interface name for point-to-point interfaces, such as serial or tunnel interfaces. This is valid because on point-to-point links, the router can forward packets out the interface without needing a specific next-hop IP address, as the remote end is implicitly known.

Answer

Two static routes to the same destination with the same preference will result in an active/backup scenario.

Answer

The default preference for a static route is 10.

Answer

A static route must always include a next-hop address.

Question 10

Which THREE factors influence the selection of the active route in the Junos routing table when multiple routes exist for the same destination? (Choose three.)

Accepted Answer

Route preference (administrative distance).. Route preference, also known as administrative distance, is a fundamental tiebreaker in Junos when multiple routing protocols provide routes to the same destination. Junos assigns a default preference value to each protocol (e.g., OSPF internal = 10, Static = 5, BGP = 170), and the route with the lowest preference value is installed as the active route in the forwarding table. This mechanism ensures deterministic selection across different protocol sources.

Answer

Number of next-hops available for each route.

Answer

Bandwidth of the outgoing interface.

Question 11

You are managing a small branch office with a Juniper SRX firewall that connects to the internet via a single ISP. The internal network uses 192.168.1.0/24. You need to configure a default route so that all internet-bound traffic goes to the ISP's next-hop 203.0.113.1. The SRX has two interfaces: ge-0/0/0 (untrust) with IP 203.0.113.2/30 and ge-0/0/1 (trust) with IP 192.168.1.1/24. You add the following configuration: 'set routing-options static route 0.0.0.0/0 next-hop 203.0.113.1'. After committing, devices on the trust network can ping the internet (e.g., 8.8.8.8) successfully. However, users report that they cannot access a specific public website hosted at 198.51.100.10. You verify that the SRX can reach that IP via ping and traceroute. What is the most likely cause of this issue?

Accepted Answer

The return traffic from the website is not reaching the SRX, possibly due to asymmetric routing or the website's firewall blocking the SRX's source IP.. The SRX can successfully ping 198.51.100.10, indicating that outbound routing and source NAT (if used) are functioning. However, users on the trust network cannot access the website. This points to a problem with the return traffic. The website may be blocking the SRX's source IP (203.0.113.2) due to a firewall rule, or there could be asymmetric routing where the return path does not pass through the SRX. Option A is incorrect because the SRX uses the untrust interface IP (203.0.113.2) as the source for outbound traffic by default (unless source NAT is configured to use the trust IP, which is unlikely). Option C is incorrect because the default route is correctly configured and working for other destinations. Option D is incorrect because there is no evidence of a more specific static route, and the SRX can reach the IP.

Answer

The SRX's source IP for outbound traffic is incorrect; it should use the untrust interface IP but is using the trust IP.

Answer

The default route is missing; the ISP must be configured as a static route.

Answer

There is a more specific static route to 198.51.100.0/24 with a different next-hop causing traffic to be sent elsewhere.

Question 12

Your company recently acquired a small office that uses a Juniper MX router to connect to two ISPs for redundancy. The router has two uplinks: xe-0/0/0 to ISP-A (next-hop 10.0.0.1) and xe-0/0/1 to ISP-B (next-hop 10.0.1.1). The router receives a full BGP table from both ISPs. You want to prefer ISP-A for most traffic, but use ISP-B as a backup. You have configured BGP with local-preference 200 on routes from ISP-A and local-preference 100 on routes from ISP-B. After committing, you check the routing table and see that for some destinations, the route from ISP-B is active despite having lower local-preference. What is the most likely reason?

Accepted Answer

The router is not receiving the ISP-A routes for those specific prefixes; perhaps ISP-A's BGP session is missing or the prefix is not advertised.. In BGP best path selection, local-preference is the first tie-breaker. Routes from ISP-A have local-preference 200, which is higher than ISP-B's 100, so they should be preferred. If the ISP-B route is active for some destinations, it means the ISP-A route for those prefixes is absent from the routing table. This could happen if ISP-A does not advertise those specific prefixes (e.g., due to a missing route or partial BGP table) or if the BGP session to ISP-A is down for those prefixes. Option A is incorrect because local-preference applies to both eBGP and iBGP. Option C is incorrect; IGP metric is compared after many BGP attributes, and local-preference takes precedence. Option D is incorrect because MED is only compared when routes are from the same AS, and even then, local-preference is considered first.

Answer

The local-preference is not applied to routes that are learned via eBGP; it only works for iBGP.

Answer

The IGP metric to the next-hop from ISP-B is lower, causing the route to be preferred.

Answer

The MED value from ISP-A is higher than from ISP-B, overriding the local-preference.

Question 13

A service provider is migrating from a legacy core network to Juniper MX series routers. In the new design, each MX router runs OSPF as the IGP with a single backbone area 0 and multiple non-backbone areas for customer aggregation. The network uses route summarization at area border routers (ABRs) to reduce routing table size. During testing, engineers notice that some customer prefixes from area 1 are not being propagated to the backbone area, even though the ABR has a valid route to those prefixes and has been configured with 'area 1 range 192.168.0.0/16'. The ABR is an MX240 running Junos 21.4R1. The 'show ospf route' command on the ABR shows the individual customer prefixes (e.g., 192.168.1.0/24) in the OSPF routing table, but the summary route is not present in the backbone area's database. Additionally, 'show ospf database summary' on a backbone router does not show the summary LSA for 192.168.0.0/16. What is the most likely cause?

Accepted Answer

The individual prefixes from area 1 may not be installed in the inet.0 routing table on the ABR, possibly due to a missing OSPF adjacency or a route filter blocking them.. The 'area range' command requires the individual prefixes to be present in the inet.0 routing table on the ABR; if they are missing due to a missing OSPF adjacency or a route filter, the summary LSA is not generated. Option A is incorrect because the summary LSA is type 3, not type 5, and an external route does not suppress the summary. Option B is incorrect because the 'area range' command does not require an interface in the area; it summarizes routes learned from the area. Option C is incorrect because the 'area range' command takes effect immediately without requiring a restart or clearing of the OSPF database.

Answer

The summary LSA is being suppressed because the ABR is also advertising a type 5 external route for the same prefix.

Answer

The ABR has no interface in area 1 that matches the summary range; the 'area range' command requires a directly connected interface.

Answer

The 'area range' command only works after a routing process restart; a 'clear ospf database' is required to regenerate LSAs.

Question 14

You are configuring a Juniper MX router to act as a BGP route reflector for your ISP network. The router has several iBGP peers, including clients and non-clients. You have configured the route-reflector-cluster-id and set the clients. After the configuration, you notice that some prefixes are not being reflected to a specific client router. The client has a valid BGP session to the route reflector and can see other prefixes. You check the BGP routing table on the route reflector and see that the missing prefixes are present but have the 'non-routable' flag. The route reflector's BGP table shows the prefix with a next-hop that is not reachable via an IGP route. What is the most likely cause?

Accepted Answer

The next-hop for the missing prefixes is not reachable via the IGP on the route reflector; the route reflector needs a route to the next-hop to advertise the prefix.. The 'non-routable' flag in a BGP table indicates that the route reflector does not have a valid route to the next-hop in its routing table. Even if the client can reach the next-hop, the route reflector must have an IGP route to the next-hop in order to advertise the prefix to clients. Option B is incorrect because cluster-id prevents loops in route reflection, not suppresses routes. Option C is incorrect because ORIGINATOR_ID does not suppress routes; it is used for loop prevention with cluster-id. Option D is incorrect because the route reflector does not modify next-hop by default; the client needs its own route to the next-hop, but the reflector must also have a route to the next-hop to advertise the prefix.

Answer

The route-reflector-cluster-id is set incorrectly, causing the route reflector to drop the route to prevent loops.

Answer

The ORIGINATOR_ID attribute from a previous route reflector is causing the route to be suppressed.

Answer

The route reflector is using the next-hop-self option and cannot resolve its own IP as a next-hop.

Question 15

You are a network engineer at a company that uses a pair of Juniper EX4300 switches in a virtual chassis (VC) configuration for the campus core. The VC is running OSPF with a single area and has multiple uplinks to an upstream router. The router is advertising a default route via OSPF. You want all inter-vlan traffic within the VC to be switched, but internet-bound traffic should be routed via the default route. You notice that some VLANs are not able to reach the internet while others can. All VLANs have a default gateway on the VC, which is the same IP (the VC's management IP). Users in the failing VLANs can ping the default gateway but cannot ping the upstream router's interface IP. What is the most likely cause?

Accepted Answer

The IRB interface for the failing VLANs does not have OSPF enabled, so the upstream router does not have a route to those subnets, and return traffic is dropped.. OSPF must be enabled on the IRB interface of each VLAN for the VC to advertise those subnets to the upstream router. If a VLAN's IRB interface does not have OSPF enabled, the upstream router does not learn a route to that subnet, and when the VC sends traffic to the upstream router, the router has no return route and drops the packets. This explains why some VLANs can reach the internet (those with OSPF on their IRB) and others cannot. Option A is incorrect because the VC is not an area border router in a single-area OSPF design; it is just an internal router. Option B is incorrect because the MAC address learning issue would affect all VLANs, not just some. Option D is incorrect because the default route from OSPF is global and not per-VLAN; the issue is not about preference but about missing routes for the specific subnets.

Answer

The VC is configured as an OSPF area border router and is not creating a summary for the failing VLANs.

Answer

The VC's MAC address table is not learning the upstream router's MAC address on the correct VLAN.

Answer

The default route from OSPF is not being installed because there is a static default route with lower preference.