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2021 Dec 400-101 ccie written passing score:
Q101. In the DiffServ model, which class represents the lowest priority with the lowest drop probability?
A. AF11
B. AF13
C. AF41
D. AF43
Answer: A
Explanation:
Assured Forwarding (AF) Behavior Group
Class 1
Class 2
Class 3
Class 4
Low Drop
AF11 (DSCP 10)
AF21 (DSCP 18)
AF31 (DSCP 26)
AF41 (DSCP 34)
Med Drop
AF12 (DSCP 12)
AF22 (DSCP 20)
AF32 (DSCP 28)
AF42 (DSCP 36)
High Drop
AF13 (DSCP 14)
AF23 (DSCP 22)
AF33 (DSCP 30)
AF43 (DSCP 38)
Reference: http://en.wikipedia.org/wiki/Differentiated_services
Q102. Which two options are contained in the MSG part of a syslog message? (Choose two.)
A. TAG field
B. CONTENT field
C. three-digit priority value
D. IP address of the sending device
E. TLS port number
Answer: A,B
Q103. Which three modes are valid for forming an EtherChannel between the ports of two switches? (Choose three.)
A. Active/active
B. Active/passive
C. Passive/passive
D. Auto/auto
E. Auto/desirable
F. Desirable/on
Answer: A,B,E
Explanation:
To configure an EtherChannel using LACP negotiation, each side must be set to either active or passive; only interfaces configured in active mode will attempt to negotiate an EtherChannel. Passive interfaces merely respond to LACP requests. PAgP behaves the same, but its two modes are refered to as desirable and auto.
Reference: http://packetlife.net/blog/2010/jan/18/etherchannel-considerations/
Q104. Refer to the exhibit.
Which option is the result of this configuration?
A. Devices in OSPF area 15 can reach the summary route 192.168.0.0/16 and its more specific subnets.
B. Devices in OSPF area 15 can reach only the more specific routes of 192.168.0.0/16.
C. Devices in OSPF area 0 can reach the summary route 192.168.0.0/16 and its more specific subnets.
D. Devices in OSPF area 0 can reach only the summary route of 192.168.0.0/16.
Answer: A
Explanation:
. area range
To consolidate and summarize routes at an area boundary, use the area range command in router configuration mode. To disable this function, use theno form of this command. Area area-id range ip-address mask [advertise | not-advertise] [cost cost] no area area-id range ip-address mask [advertise | not-advertise] [cost cost]
. Syntax Description
area-id
Identifier of the area about which routes are to be summarized. It can be specified as either a decimal value or as an IP address.
ip-address
IP address.
mask
IP address mask.
advertise
(Optional) Sets the address range status to advertise and generates a Type 3 summary link-state advertisement (LSA).
not-advertise
(Optional) Sets the address range status to DoNotAdvertise. The Type 3 summary LSA is suppressed, and the component networks remain hidden from other networks.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfospf. html
Q105. Which option describes how a router responds if LSA throttling is configured and it receives the identical LSA before the interval is set?
A. The LSA is added to the OSPF database and a notification is sent to the sending router to slow down its LSA packet updates.
B. The LSA is added to the OSPF database.
C. The LSA is ignored.
D. The LSA is ignored and a notification is sent to the sending router to slow down its LSA packet updates.
Answer: C
Explanation:
How OSPF LSA Throttling Works
The timers throttle lsa all command controls the generation (sending) of LSAs. The first LSA is always generated immediately upon an OSPF topology change, and the next LSA generated is controlled by the minimum start interval. The subsequent LSAs generated for the same LSA are rate-limited until the maximum interval is reached. The "same LSA" is defined as an LSA instance that contains the same LSA ID number, LSA type, and advertising router ID.
The timers LSA arrival command controls the minimum interval for accepting the same LSA. If an instance of the same LSA arrives sooner than the interval that is set, the LSA is dropped. It is recommended that the arrival interval be less than or equal to the hold-time interval of the timers throttle lsa all command.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_0s/feature/guide/fsolsath.html
Leading 400-101 ccie routing and switching pdf:
Q106. Which mechanism can be used on Layer 2 switches so that only multicast packets with downstream receivers are sent on the multicast router-connected ports?
A. IGMP snooping
B. Router Guard
C. PIM snooping
D. multicast filtering
Answer: C
Explanation:
Ideally, the Layer 2 device should forward the multicast transmission only out ports to which receivers are connected and also out any ports that are connected to downstream multicast routers. This configuration requires a Layer 2 device to be able to determine the ports on which multicast routers and receivers for each separate (S,G) or (*,G) multicast group are located. To facilitate intelligent forwarding of multicast traffic on the LAN, Cisco Catalyst switches support two mechanisms:
. IGMP snooping — The switch listens in or "snoops" IGMP communications between receivers and multicast routers. This snooping enables the switch to determine which ports are connected to receivers for each multicast group and which ports are connected to multicast routers.
. Cisco Group Management Protocol (CGMP) — The switch communicates with multicasts routers, with multicast routers relaying group membership information to switches.
Reference: https://www.informit.com/library/content.aspx?b=CCNP_Studies_Switching&seqNum=59
Q107. Which two statements about the command distance bgp 90 60 120 are true? (Choose two.)
A. Implementing the command is a Cisco best practice.
B. The external distance it sets is preferred over the internal distance.
C. The internal distance it sets is preferred over the external distance.
D. The local distance it sets may conflict with the EIGRP administrative distance.
E. The internal distance it sets may conflict with the EIGRP administrative distance.
F. The local distance it sets may conflict with the RIP administrative distance.
Answer: C,F
Explanation:
To allow the use of external, internal, and local administrative distances that could be a better route than other external, internal, or local routes to a node, use the distance bgp command in address family or router configuration mode. To return to the default values, use the no form of this command. distance bgp external-distance internal-distance local-distance no distance bgp
. Syntax Description
external-distance
Administrative distance for BGP external routes. External routes are routes for which the best path is learned from a neighbor external to the autonomous system. Accept table values are from 1 to 255. The default is 20. Routes with a distance of 255 are not installed in the routing table.
internal-distance
Administrative distance for BGP internal routes. Internal routes are those routes that are learned from another BGP entity within the same autonomous system. Accept table values are from 1 to 255. The default is 200. Routes with a distance of 255 are not installed in the routing table.
local-distance
Administrative distance for BGP local routes. Local routes are those networks listed with a network router configuration command, often as back doors, for that router or for networks that are being redistributed from another process. Accept table values are from 1 to 255. The default is 200. Routes with a distance of 255 are not installed in the routing table.
Defaults
external-distance: 20
internal-distance: 200
local-distance: 200
In this case, the internal distance is 60 and the external is 90, and the local distance is 120 (same as RIP).
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfbgp1. html#wp1113874
Q108. Refer to the exhibit.
Which configuration must you apply to router R2 to enable BFD?
A)
B)
C)
D)
A. Exhibit A
B. Exhibit B
C. Exhibit C
D. Exhibit D
Answer: A
Q109. Which three fields are part of a TCN BPDU? (Choose three.)
A. protocol ID
B. version
C. type
D. max-age
E. flags
F. message age
Answer: A,B,C
Q110. Which two statements about proxy ARP are true? (Choose two.)
A. It is supported on networks without ARP.
B. It allows machines to spoof packets.
C. It must be used on a network with the host on a different subnet.
D. It requires larger ARP tables.
E. It reduces the amount of ARP traffic.
Answer: B,D
Explanation:
Disadvantages of Proxy ARP
Hosts have no idea of the physical details of their network and assume it to be a flat network in which they can reach any destination simply by sending an ARP request. But using ARP for everything has disadvantages. These are some of the disadvantages:
It increases the amount of ARP traffic on your segment.
Hosts need larger ARP tables in order to handle IP-to-MAC address mappings.
Security can be undermined. A machine can claim to be another in order to intercept packets, an act called "spoofing."
It does not work for networks that do not use ARP for address resolution.
It does not generalize to all network topologies. For example, more than one router that connects two physical networks.
Reference: http://www.cisco.com/c/en/us/support/docs/ip/dynamic-address-allocation-resolution/13718-5.html