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質問 # 19
Exhibit
You are running a service provider network and must transport a customer's IPv6 traffic across your IPv4-based MPLS network using BGP You have already configured mpis ipv6-tunneling on your PE routers.
Which two statements are correct about the BGP configuration in this scenario? (Choose two.)
- A. You must configure family inet6 add-path between PE and CE routers.
- B. You must configure family inet6 unicast between PE routers
- C. You must configure family inet6 labcled-unicast between PE routers.
- D. You must configure family inet6 unicaat between PE and CE routers.
正解：C、D
解説：
Explanation
To transport IPv6 traffic over an IPv4-based MPLS network using BGP, you need to configure two address families: family inet6 labeled-unicast and family inet6 unicast. The former is used to exchange IPv6 routes with MPLS labels between PE routers, and the latter is used to exchange IPv6 routes without labels between PE and CE routers. The mpis ipv6-tunneling command enables the PE routers to encapsulate the IPv6 packets with an MPLS label stack and an IPv4 header before sending them over the MPLS network.
質問 # 20
Exhibit
Referring to the exhibit, which two statements are true? (Choose two.)
- A. The devices advertising this route into EVPN are 10 0 2 12 and 10.0.2.22.
- B. This route is learned through EBGP
- C. The device advertising this route into EVPN is 192.168.101.5.
- D. This is an EVPN Type-2 route.
正解：C、D
解説：
Explanation
This is an EVPN Type-2 route, also called a MAC/IP advertisement route, that is used to advertise host IP and MAC address information to other VTEPs in an EVPN network. The route type field in the EVPN NLRI has a value of 2, indicating a Type-2 route. The device advertising this route into EVPN is 192.168.101.5, which is the IP address of the VTEP that learned the host information from the local CE device. This IP address is carried in the MPLS label field of the route as part of the VXLAN encapsulation.
質問 # 21
A packet is received on an interface configured with transmission scheduling. One of the configured queues In this scenario, which two actions will be taken by default on a Junos device? (Choose two.)
- A. The exceeding queue will be considered to have negative bandwidth credit.
- B. The excess traffic will use bandwidth available from other queueses
- C. The exceeding queue will be considered to have positive bandwidth credit
- D. The excess traffic will be discarded
正解：A、D
解説：
Explanation
Transmission scheduling is a CoS feature that allows you to allocate bandwidth among different queues on an interface. Each queue has a configured bandwidth percentage that determines how much of the available bandwidth it can use. If a queue exceeds its allocated bandwidth, it is considered to have negative bandwidth credit and its excess traffic will be discarded by default. If a queue does not use all of its allocated bandwidth, it is considered to have positive bandwidth credit and its unused bandwidth can be shared by other queues.
質問 # 22
By default, which statement is correct about OSPF summary LSAs?
- A. Type 3 LSAs are advertised for routes in Type 1 LSAs.
- B. The metric associated with a summary route will be equal to the lowest metric associated with an individual contributing route
- C. The area-range command must be installed on all routers.
- D. All Type 2 and Type 7 LSAs will be summanzed into a single Type 5 LSA
正解：A
解説：
Explanation
OSPF uses different types of LSAs to describe different aspects of the network topology. Type 1 LSAs are also known as router LSAs, and they describe the links and interfaces of a router within an area. Type 3 LSAs are also known as summary LSAs, and they describe routes to networks outside an area but within the same autonomous system (AS). By default, OSPF will summarize routes from Type 1 LSAs into Type 3 LSAs when advertising them across area boundaries .
質問 # 23
Exhibit
You want to implement the BGP Generalized TTL Security Mechanism (GTSM) on the network Which three statements are correct in this scenario? (Choose three)
- A. BGP GTSM requires a TTL of 1 to be configured between neighbors.
- B. BGP GTSM requires a TTL of 255 to be configured between neighbors.
- C. You can implement BGP GTSM between R2, R3, and R4
- D. You can implement BGP GTSM between R2 and R1.
- E. BGP GTSM requires a firewall filter to discard packets with incorrect TTL.
正解：A、B、C
解説：
Explanation
BGP GTSM is a technique that protects a BGP session by comparing the TTL value in the IP header of incoming BGP packets against a valid TTL range. If the TTL value is within the valid TTL range, the packet is accepted. If not, the packet is discarded. The valid TTL range is from 255 - the configured hop count + 1 to
255. When GTSM is configured, the BGP packets sent by the device have a TTL of 255. GTSM provides best protection for directly connected EBGP sessions, but not for multihop EBGP or IBGP sessions because the TTL of packets might be modified by intermediate devices.
In the exhibit, we can see that R2, R3, and R4 are in the same AS (AS 20) and R1 is in a different AS (AS 10).
Based on this information, we can infer the following statements:
* You can implement BGP GTSM between R2, R3, and R4. This is not correct because R2, R3, and R4 are IBGP peers and GTSM does not provide effective protection for IBGP sessions. The TTL of packets between IBGP peers might be changed by intermediate devices or routing protocols.
* BGP GTSM requires a firewall filter to discard packets with incorrect TTL. This is not correct because BGP GTSM does not require a firewall filter to discard packets with incorrect TTL. BGP GTSM uses TCP option 19 to negotiate GTSM capability between peers and uses TCP option 20 to carry the expected TTL value in each packet. The receiver checks the expected TTL value against the actual TTL value and discards packets with incorrect TTL values.
* You can implement BGP GTSM between R2 and R1. This is correct because R2 and R1 are EBGP peers and GTSM provides effective protection for directly connected EBGP sessions. The TTL of packets between directly connected EBGP peers is not changed by intermediate devices or routing protocols.
* BGP GTSM requires a TTL of 1 to be configured between neighbors. This is not correct because BGP GTSM requires a TTL of 255 to be configured between neighbors. The sender sets the TTL of packets to 255 and the receiver expects the TTL of packets to be 255 minus the configured hop count.
* BGP GTSM requires a TTL of 255 to be configured between neighbors. This is correct because BGP GTSM requires a TTL of 255 to be configured between neighbors. The sender sets the TTL of packets to 255 and the receiver expects the TTL of packets to be 255 minus the configured hop count.
質問 # 24
Exhibit
Referring to the exhibit, what do the brackets [ ] in the AS path identify?
- A. They identify the local AS number associated with the AS path if configured on the router, or if AS path prepending is configured
- B. They identify that a BGP confederation is being used to ensure that there are no routing loops.
- C. They identify that the autonomous system number is incomplete and awaiting more information from the BGP protocol.
- D. They identify an AS set, which are groups of AS numbers in which the order does not matter
正解：D
解説：
Explanation
The brackets [ ] in the AS path identify an AS set, which are groups of AS numbers in which the order does not matter. An AS set is used when BGP aggregates routes from different ASs into a single prefix. For example, if BGP aggregates routes 10.0.0.0/16 and 10.1.0.0/16 from AS 100 and AS 200, respectively, into a single prefix 10.0.0.0/15, then the AS path for this prefix will be [100 200]. An AS set reduces the length of the AS path and prevents routing loops.
質問 # 25
Exhibit
CE-1 and CE-2 are part of a VPLS called Customer1 No connectivity exists between CE-1 and CE-2. In the process of troubleshooting, you notice PE-1 is not learning any routes for this VPLS from PE-2, and PE-2 is not learning any routes for this VPLS from PE-1.
- A. The route target must match on PE-1 and PE-2.
- B. The instance type should be changed to I2vpn.
- C. The route distinguisher must match on PE-1 and PE-2.
- D. The no-tunnel-services statement should be deleted on both PEs.
正解：A
解説：
Explanation
VPLS is a technology that provides Layer 2 VPN services over an MPLS network. VPLS uses BGP as its control protocol to exchange VPN membership information between PE routers. The route target is a BGP extended community attribute that identifies which VPN a route belongs to. The route target must match on PE routers that participate in the same VPLS instance, otherwise they will not accept or advertise routes for that VPLS.
質問 # 26
What is the correct order of packet flow through configurable components in the Junos OS CoS features?
- A. Behavior Aggregate Classifier -> Multifield Classifier -> Input Policer -> Forwarding Policy Options -> Fabric Scheduler -> Output Policer -> Scheduler/Shaper/RED -> Rewrite Marker
- B. Behavior Aggregate Classifier -> Input Policer -> Multifield Classifier -> Forwarding Policy Options -> Fabric Scheduler -> Output Policer -> Scheduler/Shaper/RED -> Rewrite Marker
- C. Behavior Aggregate Classifier -> Multifield Classifier -> Input Policer -> Forwarding Policy Options -> Fabric Scheduler -> Scheduler/Shaper/RED -> Output Policer -> Rewrite Marker
- D. Multifield Classifier -> Behavior Aggregate Classifier -> Input Policer -> Forwarding Policy Options -> Fabric Scheduler -> Output Policer -> Rewrite Marker -> Scheduler/Shaper/RED
正解：B
解説：
Explanation
The correct order of packet flow through configurable components in the Junos OS CoS features is as follows:
* Behavior Aggregate Classifier: This component uses a single field in a packet header to classify traffic into different forwarding classes and loss priorities based on predefined or user-defined values.
* Input Policer: This component applies rate-limiting and marking actions to incoming traffic based on the forwarding class and loss priority assigned by the classifier.
* Multifield Classifier: This component uses multiple fields in a packet header to classify traffic into different forwarding classes and loss priorities based on user-defined values and filters.
* Forwarding Policy Options: This component applies actions such as load balancing, filtering, or routing to traffic based on the forwarding class and loss priority assigned by the classifier.
* Fabric Scheduler: This component schedules traffic across the switch fabric based on the forwarding class and loss priority assigned by the classifier.
* Output Policer: This component applies rate-limiting and marking actions to outgoing traffic based on the forwarding class and loss priority assigned by the classifier.
* Scheduler/Shaper/RED: This component schedules, shapes, and drops traffic at the egress interface based on the forwarding class and loss priority assigned by the classifier.
* Rewrite Marker: This component rewrites the code-point bits of packets leaving an interface based on the forwarding class and loss priority assigned by the classifier.
質問 # 27
Exhibit
Referring to the exhibit, you are receiving the 192.168 0 0/16 route on both R3 and R4 from your EBGP neighbor You must ensure that R1 and R2 receive both BGP routes from the route reflector In this scenario, which BGP feature should you configure to accomplish this behavior?
- A. add-path
- B. multihop
- C. route-target
- D. multipath
正解：A
解説：
Explanation
BGP add-path is a feature that allows the advertisement of multiple paths through the same peering session for the same prefix without the new paths implicitly replacing any previous paths. This behavior promotes path diversity and reduces multi-exit discriminator (MED) oscillations. BGP add-path is implemented by adding a path identifier to each path in the NLRI. The path identifier can be considered as something similar to a route distinguisher in VPNs, except that a path ID can apply to any address family. Path IDs are unique to a peering session and are generated for each network3. In this question, we have a route reflector (RR) that receives two routes for the same prefix (192.168.0.0/16) from an EBGP neighbor. By default, the RR will only advertise its best path to its clients (R1 and R2). However, we want R1 and R2 to receive both routes from the RR. To achieve this, we need to configure BGP add-path on the RR and enable it to send multiple paths for the same prefix to its clients.
質問 # 28
Exhibit
Which two statements are true about the OSPF adjacency displayed in the exhibit? (Choose two.)
- A. There is a mismatch in the poll interval parameter between routers R1 and R2.
- B. There is a mismatch in the dead interval parameter between routers R1 and R2.
- C. There is a mismatch in the hello interval parameter between routers R1 and R2
- D. There is a mismatch in the OSPF hold timer parameter between routers R1 and R2.
正解：B、C
解説：
Explanation
The hello interval is the time interval between two consecutive hello packets sent by an OSPF router on an interface. The dead interval is the time interval after which a neighbor is declared down if no hello packets are received from it. These parameters must match between two OSPF routers for them to form an adjacency. In the exhibit, router R1 has a hello interval of 10 seconds and a dead interval of 40 seconds, while router R2 has a hello interval of 30 seconds and a dead interval of 120 seconds. This causes a mismatch and prevents them from becoming neighbors23.
質問 # 29
Exhibit
R1 and R8 are not receiving each other's routes
Referring to the exhibit, what are three configuration commands that would solve this problem? (Choose three.)
- A. Configure loops on routers in AS 65412 and advertise-peer-as on routers in AS 64498.
- B. Configure remove-private on advertisements from AS 64497 toward AS 64498
- C. Configure loops and advertise-peer-as on routers in AS 64497 and AS 64450.
- D. Configure as-override on advertisement from AS 64500 toward AS 64512.
- E. Configure remove-private on advertisements from AS 64500 toward AS 64499
正解：A、B、E
解説：
Explanation
The problem in this scenario is that R1 and R8 are not receiving each other's routes because of private AS numbers in the AS path. Private AS numbers are not globally unique and are not advertised to external BGP peers. To solve this problem, you need to do the following:
* Configure loops on routers in AS 65412 and advertise-peer-as on routers in AS 64498. This allows R5 and R6 to advertise their own AS number (65412) instead of their peer's AS number (64498) when sending updates to R7 and R8. This prevents a loop detection issue that would cause R7 and R8 to reject the routes from R5 and R62.
* Configure remove-private on advertisements from AS 64497 toward AS 64498 and from AS 64500 toward AS 64499. This removes any private AS numbers from the AS path before sending updates to external BGP peers. This allows R2 and R3 to receive the routes from R1 and R4, respectively3.
質問 # 30
Your organization manages a Layer 3 VPN for multiple customers To support advanced route than one BGP community on advertised VPN routes to remote PE routers.
Which routing-instance configuration parameter would support this requirement?
- A. vrf-export
- B. vrf-target import
- C. vrf-target export
- D. vrf-import
正解：C
解説：
Explanation
The vrf-target export parameter is used to specify one or more BGP extended community attributes that are attached to VPN routes when they are exported from a VRF routing instance to remote PE routers. This parameter allows you to control which VPN routes are accepted by remote PE routers based on their import policies. You can specify more than one vrf-target export value for a VRF routing instance to support advanced route filtering or route leaking scenarios.
質問 # 31
After a recent power outage, your manager asks you to investigate ways to automatically reduce the impact caused by suboptimal routing in your OSPF and OSPFv3 network after devices reboot.
Which three configuration statements accomplish this task? (Choose three.)
- A. set protocols ospf overload timeout 900
- B. set protocols ospf3 overload
- C. set protocols ospf3 realm ipv4-unicast overload timeout 900
- D. set protocols ospf overload
- E. set protocols oapf3 overload timeout 900
正解：A、B
解説：
Explanation
To reduce the impact of suboptimal routing in OSPF and OSPFv3 after devices reboot, you can use the overload feature to prevent a router from being used as a transit router for a specified period of time. This allows the router to stabilize its routing table before forwarding traffic for other routers. To enable the overload feature, you need to do the following:
* For OSPF, configure the overload statement under [edit protocols ospf] hierarchy level. You can also specify a timeout value in seconds to indicate how long the router should remain in overload state after it boots up. For example, set protocols ospf overload timeout 900 means that the router will be in overload state for 15 minutes after it boots up.
* For OSPFv3, configure the overload statement under [edit protocols ospf3] hierarchy level. You can also specify a realm (ipv4-unicast or ipv6-unicast) and a timeout value in seconds to indicate how long the router should remain in overload state after it boots up for each realm. For example, set protocols ospf3 realm ipv4-unicast overload timeout 900 means that the router will be in overload state for 15 minutes after it boots up for IPv4 unicast routing.
質問 # 32
Exhibit
You are examining an L3VPN route that includes the information shown in the exhibit Which statement is correct in this scenario?
- A. The information shows a Type 2 route distinguisher.
- B. The information shows a Type 0 route distinguisher
- C. The information shows a Type 1 route distinguisher.
- D. The information shows a route target
正解：B
解説：
Explanation
The information shows a Type 0 route distinguisher, which is one of the three types of route distinguishers defined by RFC 4364. A route distinguisher is a 64-bit value that is prepended to an IPv4 address to create a VPN-IPv4 address, which is unique within a VPN routing and forwarding (VRF) table. A Type 0 route distinguisher has two fields: an administrator subfield (2 bytes) and an assigned number subfield (6 bytes). The administrator subfield can be an AS number or an IP address, and the assigned number subfield can be any value assigned by the administrator. In this example, the administrator subfield is 65530 (an AS number) and the assigned number subfield is 1.
質問 # 33
Exhibit
Referring to the exhibit, PIM-SM is configured on all routers, and Anycast-RP with Anycast-PIM is used for the discovery mechanism on RP1 and RP2. The interface metric values are shown for the OSPF area.
In this scenario, which two statements are correct about which RP is used? (Choose two.)
- A. Source2 will use RP1 and Receiver2 will use RP1 for group 224.2.2.2.
- B. Source1 will use RP1 and Receiver1 will use RP2 for group 224.1 1 1
- C. Source2 will use RP2 and Received will use RP2 for group 224.2.2.2.
- D. Source1 will use RP1 and Receiver1 will use RP1 for group 224.1.1.1.
正解：C、D
解説：
Explanation
A sham link is a logical link between two PE routers that belong to the same OSPF area but are connected through an L3VPN. A sham link makes the PE routers appear as if they are directly connected, and prevents OSPF from preferring an intra-area back door link over the VPN backbone. A sham link creates an OSPF multihop neighborship between the PE routers using TCP port 646. The PEs exchange Type 1 OSPF LSAs instead of Type 3 OSPF LSAs for the L3VPN routes, which allows OSPF to use the correct metric for route selection1.
質問 # 34
Exhibit
You are attempting to summarize routes from the 203.0.113.128/25 IP block on R8 to AS 64500. You implement the export policy shown in the exhibit and all routes from the routing table stop being advertised.
In this scenario, which two steps would you take to summarize the route in BGP? (Choose two.)
- A. Add the set routing-options static route 203.0.113.123/25 discard command.
- B. Remove the from protocol bgp command from the export policy.
- C. Replace exact in the export policy with orlonger.
- D. Add the set protocols bgp family inet unicast add-path command to allow additional routes to the RIB tables. -
正解：A、C
解説：
Explanation
To summarize routes from the 203.0.113.128/25 IP block on R8 to AS 64500, you need to do the following:
* Add the set routing-options static route 203.0.113.128/25 discard command. This creates a static route for the summary prefix and discards any traffic destined to it. This is necessary because BGP can only advertise routes that are present in the routing table.
* Replace exact in the export policy with orlonger. This allows R8 to match and advertise any route that is equal or more specific than the summary prefix. The exact term only matches routes that are exactly equal to the summary prefix, which is not present in the routing table.
質問 # 35
Exhibit
Referring to the exhibit, a working L3VPN exists that connects VPN-A sites CoS is configured correctly to match on the MPLS EXP bits of the LSP, but when traffic is sent from Site-1 to Site-2, PE-2 is not classifying the traffic correctly What should you do to solve the problem?
- A. Configure the explicit-null statement on PE-1.
- B. Configure VPN prefix mapping for the PE-1_to_PE-2 LSP
- C. Configure the explicit-null statement on PE-2
- D. Set a static CoS value for the PE-1_to_PE-2 LSP
正解：A
解説：
Explanation
The explicit-null statement enables the PE router to send an MPLS label with a value of 0 (explicit null) instead of an IP header for packets destined to the VPN customer sites. This allows the penultimate hop router (the router before the egress PE router) to preserve the EXP bits of the MPLS label and pass them to the egress PE router. The egress PE router can then use these EXP bits to classify the traffic according to the CoS policy2
. In this example, PE-1 should configure the explicit-null statement under [edit protocols mpls label-switched-path PE-1_to_PE-2] hierarchy level.
質問 # 36
You are asked to protect your company's customers from amplification attacks. In this scenario, what is Juniper's recommended protection method?
- A. ASN prepending
- B. unicast Reverse Path Forwarding
- C. destination-based Remote Triggered Black Hole
- D. BGP FlowSpec
正解：C
解説：
Explanation
amplification attacks are a type of distributed denial-of-service (DDoS) attack that exploit the characteristics of certain protocols to amplify the traffic sent to a victim. For example, an attacker can send a small DNS query with a spoofed source IP address to a DNS server, which will reply with a much larger response to the victim. This way, the attacker can generate a large amount of traffic with minimal resources.
One of the methods to protect against amplification attacks is destination-based Remote Triggered Black Hole (RTBH) filtering. This technique allows a network operator to drop traffic destined to a specific IP address or prefix at the edge of the network, thus preventing it from reaching the victim and consuming bandwidth and resources. RTBH filtering can be implemented using BGP to propagate a special route with a next hop of
192.0.2.1 (a reserved address) to the edge routers. Any traffic matching this route will be discarded by the edge routers.
質問 # 37
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