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2021 Mar 400-101 test engine
Q411. DRAG DROP
Drag and drop the Cisco IOX XE subpackage on the left to the function it performs on the right.
Answer:
Q412. Which two services are used to transport Layer 2 frames across a packet-switched network? (Choose two.)
A. Frame Relay
B. ATM
C. AToM
D. L2TPv3
Answer: C,D
Explanation:
Both AToM and L2TPv3 have the common objective of transmitting packet switched traffic of L2 frames (Frame Relay, ATM, and Ethernet) across a packet-switched network.
Reference: Layer 2 VPN Architectures - Google Books Result Wei Luo, Carlos Pignataro, Anthony Chan
https://books.google.com/books?isbn=0132796864
Q413. Refer to the exhibit.
If a Layer 3 switch running OSPF in a VRF-lite configuration reports this error, which action can you take to correct the problem?
A. Set mls cef maximum-routes in the global configuration.
B. Add the vrf-lite capability to the OSPF configuration.
C. Upgrade the Layer 3 switch to a model that can support more routes.
D. Configure the control plane with a larger memory allocation to support the Cisco Express Forwarding Information Base.
Answer: A
Q414. Which two statements are true about OTV? (Choose two.)
A. It relies on flooding to propagate MAC address reachability information.
B. It uses a full mesh of point-to-multipoint tunnels to prevent head-end replication of multicast traffic.
C. It can work over any transport that can forward IP packets.
D. It supports automatic detection of multihoming.
Answer: C,D
Explanation:
The overlay nature of OTV allows it to work over any transport as long as this transport can forward IP packets. Any optimizations performed for IP in the transport will benefit the OTV encapsulated traffic. As part of the OTV control protocol, automatic detection of multihoming is included. This feature enables the multihoming of sites without requiring additional configuration or protocols
Reference: http://www.cisco.com/c/en/us/products/collateral/switches/nexus-7000-series-switches/white_paper_c11-574984.html
Q415. Which component of the BGP ORF can you use to permit and deny routing updates?
A. match
B. action
C. AFI
D. SAFI
E. ORF type
Answer: A
Regenerate 400-101 test preparation:
Q416. 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
Q417. What is a reason for 6PE to use two MPLS labels in the data plane instead of one?
A. 6PE allows penultimate hop popping and has a requirement that all P routers do not have to be IPv6 aware.
B. 6PE does not allow penultimate hop popping.
C. It allows MPLS traffic engineering to work in a 6PE network.
D. It allows 6PE to work in an MPLS network where 6VPE is also deployed.
Answer: A
Explanation:
Q. Why does 6PE use two MPLS labels in the data plane?
A. 6PE uses two labels:
. The top label is the transport label, which is assigned hop-by-hop by the Label Distribution Protocol (LDP) or by MPLS traffic engineering (TE).
. The bottom label is the label assigned by the Border Gateway Protocol (BGP) and advertised by the internal BGP (iBGP) between the Provider Edge (PE) routers.
When the 6PE was released, a main requirement was that none of the MPLS core routers (the P routers) had to be IPv6-aware. That requirement drove the need for two labels in the data plane. There are two reasons why the 6PE needs both labels.
PHP Functionality
If only the transport label were used, and if penultimate hop popping (PHP) were used, the penultimate hop router (the P router) would need to understand IPv6.
With PHP, this penultimate hop router would need to remove the MPLS label and forward the packet as an IPv6 packet. This P router would need to know that the packet is IPv6 because the P router would need to use the correct Layer 2 encapsulation type for IPv6. (The encapsulation type is different for IPv6 and IPv4; for example, for Ethernet, the encapsulation type is 0x86DD for IPv6, while it is 0x0800 for IPv4.) If the penultimate hop router is not IPv6-capable, it would likely put the Layer 2 encapsulation type for IPv4 for the IPv6 packet. The egress PE router would then believe that the packet was IPv4. There is time-to-live (TTL) processing in both the IPv4 and IPv6 headers. In IPv6, the field is called Hop Limit. The IPv4 and IPv6 fields are at different locations in the headers. Also, the Header Checksum in the IPv4 header would also need to be changed; there is no Header Checksum field in IPv6. If the penultimate hop router is not IPv6-capable, it would cause the IPv6 packet to be malformed since the router expects to find the TTL field and Header Checksum field in the header. Because of these differences, the penultimate hop router would need to know it is an IPv6 packet. How would this router know that the packet is an IPv6 packet, since it did not assign a label to the IPv6 Forwarding Equivalence Class (FEC), and there is no encapsulation field in the MPLS header? It could scan for the first nibble after the label stack and determine that the packet is IPv6 if the value is 6. However, that implies that the penultimate hop router needs to be IPv6-capable. This scenario could work if the explicit null label is used (hence no PHP). However, the decision was to require PHP.
Load Balancing
Typical load balancing on a P router follows this process. The P router goes to the end of the label stack and determines if it is an IPv4 packet by looking at the first nibble after the label stack.
. If the nibble has a value of 4, the MPLS payload is an IPv4 packet, and the P router load balances by hashing the source and destination IPv4 addresses.
. If the P router is IPv6-capable and the value of the nibble is 6, the P router load balances by hashing the source and destination IPv6 addresses.
. If the P router is not IPv6-capable and the value of the nibble is not 4 (it could be 6 if the packet is an IPv6 packet), the P router determines it is not an IPv4 packet and makes the load balancing decision based on the bottom label. In the 6PE scenario, imagine there are two egress PE routers advertising one IPv6 prefix in BGP towards the ingress PE router. This IPv6 prefix would be advertised with two different labels in BGP. Hence, in the data plane, the bottom label would be either of the two labels. This would allow a P router to load balance on the bottom label on a per-flow basis. If 6PE used only the transport label to transport the 6PE packets through the MPLS core, the P routers would not be able to load balance these packets on a per-flow basis unless the P routers were IPv6-capable. If the P routers were IPv6-capable, they could use the source and destination IPv6 addresses in order to make a load balancing decision.
Reference: http://www.cisco.com/c/en/us/support/docs/multiprotocol-label-switching-mpls/mpls/116061-qa-6pe-00.html
Q418. DRAG DROP
Drag and drop the BGP attribute on the left to the correct category on the right.
Answer:
Q419. Which three protocols can use enhanced object tracking? (Choose three.)
A. HSRP
B. Proxy-ARP
C. VRRP
D. GLBP
E. NTP
F. DHCP
Answer: A,C,D
Explanation:
The Enhanced Object Tracking feature separates the tracking mechanism from HSRP and creates a separate standalone tracking process that can be used by other processes and HSRP. This feature allows tracking of other objects in addition to the interface line-protocol state. A client process such as HSRP, Virtual Router Redundancy Protocol (VRRP), or Gateway Load Balancing Protocol (GLBP), can register its interest in tracking objects and then be notified when the tracked object changes state.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/ipapp/configuration/15-mt/iap-15-mt-book/iap-eot.html
Q420. Which circumstance can cause packet loss due to a microburst?
A. slow convergence
B. a blocked spanning-tree port
C. process switching
D. insufficient buffers
Answer: D
Explanation:
Micro-bursting is a phenomenon where rapid bursts of data packets are sent in quick succession, leading to periods of full line-rate transmission that can overflow packet buffers of the network stack, both in network endpoints and routers and switches inside the network.
Symptoms of micro bursts will manifest in the form of ignores and/ or overruns (also shown as accumulated in “input error” counter within show interface output). This is indicative of receive ring and corresponding packet buffer being overwhelmed due to data bursts coming in over extremely short period of time (microseconds).
Reference: http://ccieordie.com/?tag=micro-burst