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Q1. When implementing LDP, what is liberal label retention mode?
A. To reduce the convergence time, the LSR will retain all the received labels in its LIB even if all the neighbor LSRs go down temporary
B. The LSR can assign it's own label for each destination network even though it has not been assigned a next hop label from the neighbor LSR
C. The LSR will store the label received from the downstream LSRs in its LIB even if the downstream LSRs are not the next hop for the destination
D. The LSR will not perform PHP if it is operating in liberal label retention mode
Answer: C
Explanation:
By default, LDP accepts labels (as remote bindings) for all prefixes from all peers. LDP operates in liberal label retention mode, which instructs LDP to keep remote bindings from all peers for a given prefix. For security reasons, or to conserve memory, you can override this behavior by configuring label binding acceptance for set of prefixes from a given peer.
The ability to filter remote bindings for a defined set of prefixes is also referred to as LDP inbound label filtering
Q2. Which OSPF feature allows a router with redundant route processors to maintain its OSPF state and adjacencies across planned and unplanned RP switchovers and does this by
checkpointing state information from OSPF on the active RP to the standby RP? This feature does not require the OSPF neighbor to support graceful restart.
A. NSR
B. NSF
C. BFD
D. MTR
E. SDR
Answer: A
Explanation:
Continuous Forwarding An important aspect of high availability is maintenance of traffic forwarding, even in the case of control-plane switchovers. Cisco IOS XR Software has several built-in features that can provide continuous forwarding, including RSP stateful switchover (SSO), Nonstop Forwarding (NSF), Graceful Restart, and NSR.
NSF: Cisco IOS XR Software supports forwarding without traffic loss during a brief outage of the control plane through signaling and routing protocol implementations for Graceful Restart extensions as standardized by the IETF. In addition to standards compliance, this implementation has been compatibility tested with Cisco IOS Software and third-party operating systems.
Graceful Restart: This control-plane mechanism ensures high availability by allowing detection and recovery from failure conditions while preserving NSF services. Graceful Restart is a way to recover from signaling and control-plane failures without affecting the forwarding plane. Cisco IOS XR Software uses this feature and a combination of check pointing, mirroring, RSP redundancy, and other system resiliency features to recover prior to timeout and avoid service downtime as a result of network reconvergence.
NSR: This feature allows for the forwarding of data packets to continue along known routes while the routing protocol information is being refreshed following a processor switchover.
NSR maintains protocol sessions and state information across SSO functions for services such as Multiprotocol Label Switching (MPLS) VPN. TCP connections and the routing protocol sessions are migrated from the active RSP to the standby RSP after the RSP failover without letting the peers know about the failover. The sessions terminate locally on the failed RSP, and the protocols running on the standby RSP reestablish the sessions after the standby RSP goes active, without the peer detecting the change. You can also use NSR with Graceful Restart to protect the routing control plane during switchovers. The Cisco IOS XR Operating System provides system resiliency through a comprehensive set of high-availability features including modularity, process restart, fault handling, continuous forwarding, and upgradability.
Q3. In which network environment is IS-IS adjacency check important?
A. in a multitopology environment where there are different instances of IS-IS running on the same router
B. in an IPv4/IPv6 environment and running single-topology IS-IS
C. when a level L1/L2 IS-IS router is neighboring with a Level 1 only or Level 2 only router
D. when IS-IS neighbors are in an NBMA environment like over Frame Relay
E. when IS-IS neighbors are in a broadcast environment like an Ethernet LAN
Answer: B
Explanation:
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Q4. Refer to the exhibit.
XR1 must have XR4 as the primary exit point for only the first three subnets received from AS 100 and may not impact the rest of the subnets. Which configuration on XR1 is correct?
A. prefix-set PREFER 100.100.100.0/30 le 32 route-policy LP if destination in PREFER then set local-preference 200 endif
B. route-policy LP if destination in (100.100.100.0/30 le 32) then set local-preference 200 else pass endif
C. prefix-set PREFER 100.100.100.0/29 le 32 route-policy LP if destination in PREFER then set local-preference 200 else pass endif
D. route-policy LP if destination in (100.100.100.0/29 le 32) then set local preference 200 else set local-preference 100 endif
Answer: B
Q5. When using the show bgp ipv6 unicast summary command to verify the IPv6 BGP session status with the IPv6 BGP peers, you noticed the "St/PfxRcd" status for one of the IPv6 BGP peers is in the "Active" state. What does the "Active" state indicate?
A. The IPv6 BGP session has been established with the IPv6 BGP peer.
B. The router is in the process of sending BGP routing updates to the IPv6 BGP peer.
C. The router is in the process of establishing the IPv6 BGP session with the IPv6 BGP peer.
D. The router is exchanging BGP notification messages with its IPv6 BGP peer.
Answer: C
Q6. Which two mandatory tasks must an IS-IS NSF-capable router perform for RP switchover? (Choose two.)
A. Relearn the available IS-IS neighbors.
B. Reacquire the contents of the LSD.
C. Reset peering with the available IS-IS neighbors.
D. Keep the existing contents of the LSD.
E. Rediscover DIS for each link segment.
Answer: A,B
Q7. What is recursive lookup in BGP and how does it work?
A. The router looks up the EBGP route and the EBGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the EBGP next hop using the IBGP.
B. The router looks up the IBGP route and the IBGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the IBGP next hop using the EBGP.
C. The router looks up the BGP route and the BGP next hop to reach a destination in the remote AS. Then the router looks up the route to reach the BGP next hop using the IGP.
D. The router looks up the route and the next hop to reach a destination in the remote AS using the IGP. Then the router looks up the route to reach the next hop using BGP.
E. The router perform three routing lookups to determine the route to reach a destination in the remote AS. The first lookup is done using EBGP, the second lookup is done using IBGP, and the third lookup is done using the IGP.
Answer: C
Explanation:
A few different approaches are available to deal with iBGP and synchronization. We may turn on the synchronization option on our routers and wait for the IGP to have a route for the destination before it’s advertised to peers. Another option is to simply use a full mesh, so that iBGP convergence isn’t an issue. Clearly that isn’t going to happen when a network’s core needs to scale: it will implement something like reflectors that cause iBGP’s full mesh to be broken. The real alternative, if you don’t enable synchronization, is to use route recursion. A recursive route lookup uses the BGP next-hop attribute to actually make a different route lookup. The IGP can use the destination network instead of the AS-path to determine where it gets sent. Even if the iBGP hasn’t converged, the routers will still know how to get to that network, since it will exist in the router it was advertised from, who will know the next-hop.
Q8. Nonstop Forwarding works with the Stateful Switchover feature in Cisco IOS and IOS XR software. Which three restrictions for OSPF are true? (Choose three.)
A. OSPF NSF for virtual links is not supported.
B. OSPF NSF for virtual links is supported.
C. OSPF NSF for sham links is not supported.
D. OSPF NSF for sham links is supported.
E. OSPF NSF supports NSF/SSO for IPv6 traffic only.
F. OSPF NSF supports NSF/SSO for IPv4 traffic only.
Answer: A,C,F
Q9. Refer to the exhibit.
Which configuration is required on XR2 to enable MD5 IS-IS Authentication between R1 and XR2 using the password CISCO?
A. Router isis ABC interface GigabitEthernet0/0/0/0 hello-password encrypted CISCO
B. Router isis ABC interface GigabitEthernet0/0/0/0 hello-password hmac-md5 CISCO
C. Router isis ABC lsp-password hmac-md5 CISCO
D. Router isis ABC lsp-password encrypted CISCO
Answer: B
Q10. Refer to the network diagram in the exhibit.
Assuming the IBGP session within AS 64500 was established using the loopback 0 interface between the two routers, by default, what will be the next hop of the routes from AS 64501 when the routes appear on the router running IBGP only in AS 64500?
A. 192.168.101.11
B. 192.168.101.10
C. 10.1.1.1
D. 10.0.1.1
E. 10.1.10.1
Answer: A