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2021 Apr 400-101 free exam questions
Q421. Which three features are common to OSPF and IS-IS? (Choose three.)
A. They both maintain a link-state database from which a Dijkstra-based SPF algorithm computes a shortest path tree.
B. They both use DR and BDR in the broadcast network.
C. They both use hello packets to form and maintain adjacencies.
D. They both use NSSA and stub type areas to scale the network design.
E. They both have areas to form a two-level hierarchical topology.
Answer: A,C,E
Q422. Which TCP mechanism prevents the sender from sending data too quickly for the receiver to process?
A. Congestion control
B. Error detection
C. Selective acknowledgement
D. Flow control
Answer: D
Explanation:
In data communications, flow control is the process of managing the rate of data transmission between two nodes to prevent a fast sender from overwhelming a slow receiver. It provides a mechanism for the receiver to control the transmission speed, so that the receiving node is not overwhelmed with data from transmitting node.
Reference: http://en.wikipedia.org/wiki/Flow_control_(data)
Q423. Which option is the default maximum age of the MAC address table?
A. 300 seconds
B. 500 seconds
C. 1200 seconds
D. 3600 seconds
Answer: A
Explanation:
To configure the maximum aging time for entries in the Layer 2 table, use the mac-address-table aging-time command in global configuration mode.
Syntax Description
seconds
MAC address table entry maximum age. Valid values are 0, and from 5 to 1000000 seconds. Aging time is counted from the last time that the switch detected the MAC address. The default value is 300 seconds.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/lanswitch/command/reference/lsw_book/lsw_m1. html
Q424. Which two values comprise the VPN ID for an MPLS VPN? (Choose two.)
A. an OUI
B. a VPN index
C. a route distinguisher
D. a 16-bit AS number
E. a 32-bit IP address
Answer: A,B
Explanation:
Each MPLS VPN ID defined by RFC 2685 consists of the following elements:
. An Organizational Unique Identifier (OUI), a three-octet hex number: The IEEE Registration Authority assigns OUIs to any company that manufactures
components under the ISO/IEC 8802 standard. The OUI is used to generate universal LAN MAC addresses and protocol identifiers for use in local and metropolitan area network applications. For example, an OUI for Cisco Systems is 00-03-6B (hex).
. A Virtual Private Network (VPN) index: a four-octet hex number, which identifies the VPN within the company.
Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/mp_l3_vpns/configuration/15-mt/mp-l3-vpns-15-mt-book/mp-assgn-id-vpn.html
Q425. On which three options can Cisco PfR base its traffic routing? (Choose three.)
A. Time of day
B. An access list with permit or deny statements
C. Load-balancing requirements
D. Network performance
E. User-defined link capacity thresholds
F. Router IOS version
Answer: C,D,E
Explanation:
Key Advantages of using PfR for Load balancing:
. Utilization based load-balancing: PfR takes real-time link utilization into account when load balancing the links. This will ensure that a link will not go beyond a certain percentage of its maximum capacity (75% by default).
. Application Performance based Load Balancing: PfR does not randomly forward traffic through one link or another. It takes application performance requirements into consideration and then forwards the traffic through a link which meets the performance policy requirements. PfR also load balances the link at the same time.
. Bi-directional Solution: PfR is a bi-directional load balancing solution which influences outbound as well as in-bound traffic.
. Consolidated Centralized View: PfR offers consolidated and centralized view of the state of all external links in the network. At any given time, the network administrator can see the current link utilization (in kbps and percentage of its capacity), maximum link threshold, and the policies applied to the links in the network.
Reference: http://docwiki.cisco.com/wiki/PfR:Solutions:InternetOutboundLoadBalancing
Renewal 400-101 answers:
Q426. Refer to the exhibit.
If you change the Spanning Tree Protocol from pvst to rapid-pvst, what is the effect on the interface Fa0/1 port state?
A. It transitions to the listening state, and then the forwarding state.
B. It transitions to the learning state and then the forwarding state.
C. It transitions to the blocking state, then the learning state, and then the forwarding state.
D. It transitions to the blocking state and then the forwarding state.
Answer: C
Explanation:
First, the port will transition to the blocking state, immediately upon the change, then it will transition to the new RSTP states of learning and forwarding.
Port States
There are only three port states left in RSTP that correspond to the three possible operational states. The 802.1D disabled, blocking, and listening states are merged into a unique 802.1w discarding state.
STP (802.1D) Port State
RSTP (802.1w) Port State
Is Port Included in Active Topology?
Is Port Learning MAC Addresses?
Disabled
Discarding
No
No
Blocking
Discarding
No
No
Listening
Discarding
Yes
No
Learning
Learning
Yes
Yes
Forwarding
Forwarding
Yes
Yes
Q427. Refer to the exhibit.
Which statement is true?
A. IS-IS has been enabled on R4 for IPv6, single-topology.
B. IS-IS has been enabled on R4 for IPv6, multitopology.
C. IS-IS has been enabled on R4 for IPv6, single-topology and multitopology.
D. R4 advertises IPv6 prefixes, but it does not forward IPv6 traffic, because the protocol has not been enabled under router IS-IS.
Answer: A
Explanation:
When working with IPv6 prefixes in IS-IS, you can configure IS-IS to be in a single topology for both IPv4 and IPv6 or to run different topologies for IPv4 and IPv6. By default, IS-IS works in single-topology mode when activating IPv4 and IPv6. This means that the IS-IS topology will be built based on IS Reachability TLVs. When the base topology is built, then IPv4 prefixes (IP Reachability TLV) and IPv6 prefixes (IPv6 Reachability TLV) are added to each node as leaves, without checking if there is IPv6 connectivity between nodes.
Reference: https://blog.initialdraft.com/archives/3381/
Q428. Which statement about the feasibility condition in EIGRP is true?
A. The prefix is reachable via an EIGRP peer that is in the routing domain of the router.
B. The EIGRP peer that advertises the prefix to the router has multiple paths to the destination.
C. The EIGRP peer that advertises the prefix to the router is closer to the destination than the router.
D. The EIGRP peer that advertises the prefix cannot be used as a next hop to reach the destination.
Answer: C
Explanation:
The advertised metric from an EIGRP neighbor (peer) to the local router is called Advertised Distance (or reported distance) while the metric from the local router to that network is called Feasible Distance. For example, R1 advertises network 10.10.10.0/24 with a metric of 20 to R2. For R2, this is the advertised distance. R2 calculates the feasible distance by adding the metric from the advertised router (R1) to itself. So in this case the feasible distance to network 10.10.10.0/24 is 20 + 50 = 70.
Before a router can be considered a feasible successor, it must pass the feasibility condition rule. In short, the feasibility condition says that if we learn about a prefix from a neighbor, the advertised distance from that neighbor to the destination must be lower than our feasible distance to that same destination. Therefore we see the Advertised Distance always smaller than the Feasible Distance to satisfy the feasibility condition.
Q429. Which two message types allow PIM snooping to forward multicast traffic? (Choose two.)
A. hello messages
B. leave messages
C. membership query messages
D. bidirectional PIM DF election messages
Answer: A,D
Q430. Which option describes what the default RT filter indicates when you implement the BGP RT constrained route distribution feature?
A. A peer receives only a default route for each VRF.
B. A peer receives all routes, regardless of the RT value.
C. A peer receives routes only for RTs that are used on that router.
D. A peer receives no routes, regardless of the RT value.
Answer: B