Deploying Cisco Service Provider Advanced Routing (SPADVROUTE)

Here you have the best Cisco 642-885 practice exam questions

  • You have 127 total questions to study from
  • Each page has 5 questions, making a total of 26 pages
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  • This questions were last updated on October 13, 2025
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Question 1 of 127
When implementing source-based remote-triggered black hole filtering, which two configurations are required on the edge routers that are not the signaling router? (Choose two.)
    Correct Answer: A, C
    Source-Based RTBH Filtering -
    With destination-based black holing, all traffic to a specific destination is dropped after the black hole has been activated, regardless of where it is coming from.
    Obviously, this could include legitimate traffic destined for the target. Source-based black holes provide the ability to drop traffic at the network edge based on a specific source address or range of source addresses.
    If the source address (or range of addresses) of the attack can be identified (spoofed or not), it would be better to drop all traffic at the edge based on the source address, regardless of the destination address. This would permit legitimate traffic from other sources to reach the target. Implementation of source-based black hole filtering depends on Unicast Reverse Path Forwarding (uRPF), most often loose mode uRPF.
    Loose mode uRPF checks the packet and forwards it if there is a route entry for the source IP of the incoming packet in the router forwarding information base
    (FIB). If the router does not have an FIB entry for the source IP address, or if the entry points to a null interface, the Reverse Path Forwarding (RPF) check fails and the packet is dropped, as shown in Figure 2. Because uRPF validates a source IP address against its FIB entry, dropping traffic from specific source addresses is accomplished by configuring loose mode uRPF on the external interface and ensuring the RPF check fails by inserting a route to the source with a next hop of Null0.
    This can be done by using a trigger device to send IBGP updates. These updates set the next hop for the source IP to an unused IP address that has a static entry at the edge, setting it to null as shown in Figure 2.
    Exam 642-885: Question 1 - Image 1 AC
Question 2 of 127
Refer to the topology diagram shown in the exhibit and the partial configurations shown below.
Exam 642-885: Question 2 - Image 1

Once the attack from 209.165.201.144/28 to 209.165.202.128/28 has been detected, which additional configurations are required on the P1 IOS-XR router to implement source-based remote-triggered black hole filtering?

!
router bgp 123
address-family ipv4 unicast
redistribute static route-policy test
!
    Correct Answer: C
    Source-Based RTBH Filtering -
    With destination-based black holing, all traffic to a specific destination is dropped after the black hole has been activated, regardless of where it is coming from.
    Obviously, this could include legitimate traffic destined for the target. Source-based black holes provide the ability to drop traffic at the network edge based on a specific source address or range of source addresses.
    If the source address (or range of addresses) of the attack can be identified (spoofed or not), it would be better to drop all traffic at the edge based on the source address, regardless of the destination address. This would permit legitimate traffic from other sources to reach the target. Implementation of source-based black hole filtering depends on Unicast Reverse Path Forwarding (uRPF), most often loose mode uRPF. Loose mode uRPF checks the packet and forwards it if there is a route entry for the source IP of the incoming packet in the router forwarding information base (FIB). If the router does not have an FIB entry for the source
    IP address, or if the entry points to a null interface, the Reverse Path Forwarding (RPF) check fails and the packet is dropped, as shown in Figure 2. Because uRPF validates a source IP address against its FIB entry, dropping traffic from specific source addresses is accomplished by configuring loose mode uRPF on the external interface and ensuring the RPF check fails by inserting a route to the source with a next hop of Null0. This can be done by using a trigger device to send
    IBGP updates. These updates set the next hop for the source IP to an unused IP address that has a static entry at the edge, setting it to null as shown in Figure 2.
    Exam 642-885: Question 2 - Image 2 C
Question 3 of 127
In Cisco IOS-XR, the maximum-prefix command, to control the number of prefixes that can be installed from a BGP neighbor, is configured under which configuration mode?
    Correct Answer: D

Question 4 of 127
In Cisco IOS-XR, the ttl-security command is configured under which configuration mode?
    Correct Answer: C

Question 5 of 127
Refer to the exhibit.
Exam 642-885: Question 5 - Image 1

Given the partial BGP configuration, which configuration correctly completes the Cisco IOS-XR route reflector configuration where both the 1.1.1.1 and 2.2.2.2 routers are the clients and the 3.3.3.3 router is a non-client IBGP peer?
    Correct Answer: C