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2021 Jan 400-101 ccie routing and switching pdf:
Q401. Which three statements about the route preference of IS-IS are true? (Choose three.)
A. An L1 path is preferred over an L2 path.
B. An L2 path is preferred over an L1 path.
C. Within each level, a path that supports optional metrics is preferred over a path that supports only the default metric.
D. Within each level of metric support, the path with the lowest metric is preferred.
E. The Cisco IS-IS implementation usually performs equal cost path load balancing on up to eight paths.
F. Both L1 and L2 routes will be installed in the routing table at the same time.
Answer: A,C,D
Explanation:
Given multiple possible routes to a particular destination, an L1 path is preferred over an L2 path. Within each level, a path that supports the optional metrics is preferred over a path that supports only the default metric. (Again, Cisco supports only the default metric, so the second order of preference is not relevant to Cisco routers.) Within each level of metric support, the path with the lowest metric is preferred. If multiple equal-cost, equal-level paths are found by the Decision process, they are all entered into the route table. The Cisco IS-IS implementation usually performs equal-cost load balancing on up to six paths.
Reference: http://www.realccielab.org/operation-of-integrated-is-is.html
Q402. Which BGP aggregate address configuration advertises only the aggregate address, with attributes inherited from the more specific routes?
A. summary-only as-set
B. as-set
C. summary
D. summary-only
Answer: A
Explanation:
Example:
router bgp 300
neighbor 2.2.2.2 remote-as 100
neighbor 3.3.3.3 remote-as 200
neighbor 4.4.4.4 remote-as 400
aggregate-address 160.0.0.0 255.0.0.0 summary-only as-set
!--- With the as-set configuration command, the aggregate
!--- inherits the attributes of the more-specific routes.
Reference: http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/5441-aggregation.html
Q403. Which two statements are true about VPLS? (Choose two.)
A. It can work over any transport that can forward IP packets.
B. It provides integrated mechanisms to maintain First Hop Resiliency Protocols such as HSRP, VRRP, or GLBP.
C. It includes automatic detection of multihoming.
D. It relies on flooding to propagate MAC address reachability information.
E. It can carry a single VLAN per VPLS instance.
Answer: D,E
Explanation:
VPLS relies on flooding to propagate MAC address reachability information. Therefore, flooding cannot be prevented.
VPLS can carry a single VLAN per VPLS instance. To multiplex multiple VLANs on a single instance, VPLS uses IEEE QinQ.
Reference: http://www.cisco.com/c/en/us/products/collateral/switches/nexus-7000-series-switches/white_paper_c11-574984.html
Q404. Refer to the exhibit.
All switches have default bridge priorities, and originate BPDUs with MAC addresses as indicated. The numbers shown are STP link metrics. Which two ports are forwarding traffic after STP converges? (Choose two.)
A. The port connecting switch SWD with switch SWE
B. The port connecting switch SWG with switch SWF
C. The port connecting switch SWC with switch SWE
D. The port connecting switch SWB with switch SWC
Answer: C,D
Explanation:
Here, we know SWB to SWC are forwarding because we already identified the blocking port. So for the last correct answer let’s consider what must be done to prevent a switch loop between SWC/SWD/SWE. SWE to SWD will be blocked because SWC has a lower MAC address so it wins the forwarding port. And to look at it further, you could try to further understand what would happen with ports on SWG. Would the ports on SWG try to go through SWE or SWF? SWE has the lower MAC address so the port from SWG to SWE would win the forwarding election. Therefore, answer B could never be correct.
Q405. Which two improvements do SIA-Query and SIA-Reply messages add to EIGRP? (Choose two.)
A. Stuck-in-active conditions are solved faster.
B. They prevent a route from going into the stuck-in-active state.
C. They help in the localization of the real failure in the network.
D. The EIGRP adjacency between two neighbors never goes down.
Answer: A,C
Leading ccie written exam:
Q406. Which statement about the function of poison reverse in EIGRP is true?
A. It tells peers to remove paths that previously might have pointed to this router.
B. It tells peers to remove paths to save memory and bandwidth.
C. It provides reverse path information for multicast routing.
D. It tells peers that a prefix is no longer reachable.
Answer: A
Explanation:
Poison Reverse in EIGRP states: “Once you learn of a route through an interface, advertise it as unreachable back through that same interface”. For more information please read here. http://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/16406-eigrp-toc.html#splithorizon.
Q407. Refer to the exhibit.
Routers R1 and R2 are configured as shown, and traffic from R1 fails to reach host 209.165.201.254.
Which action can you take to correct the problem?
A. Ensure that R2 has a default route in its routing table.
B. Change the OSPF area type on R1 and R2.
C. Edit the router configurations so that address 209.165.201.254 is a routable address.
D. Remove the default-information originate command from the OSPF configuration of R2.
Answer: A
Explanation:
Not sure that any of these answers are correct, it appears that this configuration is valid for reaching that one specific host IP. Answer A does have a route to that host so it would not need a default route to get to it. Choice B is incorrect as the area types have nothing to do with this. C is incorrect as that IP address is routable, and D is needed so that R1 will have a default route advertised to it from R2 so that it can reach this destination.
Q408. Which three statements about EIGRP wide metrics are true? (Choose three.)
A. The maximum metric is 65536.
B. The default delay is 1,000,000 picoseconds.
C. They allow up to 100 hops.
D. They allow up to 256 hops.
E. The default delay is 1,000,000 milliseconds.
F. The maximum metric is 51200.
Answer: A,B,C
Q409. By default, how does a GET VPN group member router handle traffic when it is unable to register to a key server?
A. All traffic is queued until registration is successful or the queue is full.
B. All traffic is forwarded through the router unencrypted.
C. All traffic is forwarded through the router encrypted.
D. All traffic through the router is dropped.
Answer: B
Explanation:
In the basic GETVPN configuration, the traffic passing through group members will be sent in clear until it registers with the Key Server. This is because the crypto ACL is configured on the KS and GM will get that information only after the registration is successful. This means for a short period of time the traffic can go out unencrypted after a GM is booted up or the existing GETVPN session is cleared manually. This mode is called “fail open” and it is the default behavior. This behavior can be turned off by configuring “Fail Close” mode on the GMs.
Reference: http://www.cisco.com/c/en/us/products/collateral/security/group-encrypted-transport-vpn/deployment_guide_c07_554713.html
Q410. Which three options are best practices for implementing a DMVPN? (Choose three.)
A. Use IPsec in tunnel mode.
B. Implement Dead Peer Detection to detect communication loss.
C. Configure AES for encryption of transported data.
D. Configure SHA-1 for encryption of transported data.
E. Deploy IPsec hardware acceleration to minimize router memory overhead.
F. Configure QoS services only on the head-end router.
Answer: A,B,C
Explanation:
Best Practices Summary for Hub-and-Spoke Deployment Model
This section describes the best practices for a dual DMVPN cloud topology with the hub-and-spoke deployment, supporting IP multicast (IPmc) traffic including routing protocols.
The following are general best practices:
. Use IPsec in transport mode
. Configure Triple DES (3DES) or AES for encryption of transported data (exports of encryption algorithms to certain countries may be prohibited by law).
Implement Dead Peer Detection (DPD) on the spokes to detect loss of communication between peers.
. Deploy hardware-acceleration of IPsec to minimize router CPU overhead, to support traffic with low latency and jitter requirements, and for the highest performance for cost.
. Keep IPsec packet fragmentation to a minimum on the customer network by setting MTU size or using Path MTU Discovery (PMTUD).
. Use Digital Certificates/Public Key Infrastructure (PKI) for scalable tunnel authentication.
. Configure a routing protocol (for example, EIGRP, BGP or OSPF) with route summarization help alleviate interface congestion issues and to attempt to keep higher priority traffic from being dropped during times of congestion.
Reference: http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/DMVPDG/DMV PN_1.html