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2021 Apr 400-101 exam question
Q221. Refer to the exhibit.
How can Router X in AS70000 peer with Router Y in AS65000, in case Router Y supports only 2-byte ASNs?
A. Router X should be configured with a remove-private-as command, because this will establish the peering session with a random private 2-byte ASN.
B. It is not possible. Router Y must be upgraded to an image that supports 4-byte ASN.
C. Router Y should be configured with a 4-byte AS using the local-as command.
D. Router X should be configured with a 2-byte AS using the local-as command.
Answer: D
Explanation:
Since router Y does not support 4-byte ASN,s it will not understand any AS numbers larger than 65535, so router X should use the local-as command on the peering statement to router Y to so that it sends in a 2-byte ASN to router Y.
Q222. 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
Q223. Which two statements about the BGP community attribute are true? (Choose two.)
A. Routers send the community attribute to all BGP neighbors automatically.
B. A router can change a received community attribute before advertising it to peers.
C. It is a well-known, discretionary BGP attribute.
D. It is an optional transitive BGP attribute.
E. A prefix can support only one community attribute.
Answer: B,D
Explanation:
A community is a group of prefixes that share some common property and can be configured with the BGP community attribute. The BGP Community attribute is an optional transitive attribute of variable length. The attribute consists of a set of four octet values that specify a community. The community attribute values are encoded with an Autonomous System (AS) number in the first two octets, with the remaining two octets defined by the AS. A prefix can have more than one community attribute. A BGP speaker that sees multiple community attributes in a prefix can act based on one, some or all the attributes. A router has the option to add or modify a community attribute before the router passes the attribute on to other peers.
Reference:
http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/28784-bgp-community.html
Q224. Which three types of traffic are protected when you implement IPsec within an IPv6-in-IPv4 tunnel? (Choose three.)
A. IPv6 link-local traffic
B. IPv6 multicast traffic
C. IPv6 unicast traffic
D. IPv4 tunnel control traffic
E. IPv4 broadcast traffic
F. IPv6 broadcast traffic
Answer: A,B,C
Q225. DRAG DROP
Drag and drop the argument of the mls ip cef load-sharing command on the left to the function it performs on the right.
Answer:
Abreast of the times 400-101 actual test:
Q226. Refer to the exhibit.
Router A and router B are physically connected over an Ethernet interface, and IS-IS is configured as shown. Which option explains why the IS-IS neighborship is not getting formed between router A and router B?
A. same area ID
B. same N selector
C. same domain ID
D. same system ID
Answer: D
Explanation:
With IS-IS, the LSP identifier is derived from the system ID (along with the pseudonode ID and LSP number). Each IS is usually configured with one NET and in one area; each system ID within an area must be unique. The big difference between NSAP style addressing and IP style addressing is that, in general, there will be a single NSAP address for the entire router, whereas with IP there will be one IP address per interface. All ISs and ESs in a routing domain must have system IDs of the same length. All routers in an area must have the same area address. All Level 2 routers must have a unique system ID domain-wide, and all Level 1 routers must have a unique system ID area-wide.
Reference: http://www.cisco.com/en/US/products/ps6599/products_white_paper09186a00800a3e6f.sh tml
Q227. Which TCP feature allows a client to request a specific packet that was lost?
A. flow control
B. sliding window
C. fast recovery
D. selective acknowledgment
Answer: D
Explanation:
. TCP Selective Acknowledgment
The TCP Selective Acknowledgment feature improves performance if multiple packets are lost from one TCP window of data. Prior to this feature, because of limited information available from cumulative acknowledgments, a TCP sender could learn about only one lost packet per-round-trip time. An aggressive sender could choose to resend packets early, but such re-sent segments might have already been successfully received. The TCP selective acknowledgment mechanism helps improve performance. The receiving TCP host returns selective acknowledgment packets to the sender, informing the sender of data that has been received. In other words, the receiver can acknowledge packets received out of order. The sender can then resend only missing data segments (instead of everything since the first missing packet). Prior to selective acknowledgment, if TCP lost packets 4 and 7 out of an 8-packet window, TCP would receive acknowledgment of only packets 1, 2, and 3. Packets 4 through 8 would need to be re-sent. With selective acknowledgment, TCP receives acknowledgment of packets 1, 2, 3, 5, 6, and 8. Only packets 4 and 7 must be re-sent. TCP selective acknowledgment is used only when multiple packets are dropped within one TCP window. There is no performance impact when the feature is enabled but not used. Use the ip tcp selective-ack command in global configuration mode to enable TCP selective acknowledgment.
Refer to RFC 2021 for more details about TCP selective acknowledgment.
Q228. Now that we’ve generated the key, our next step would be to configure our vty lines for SSH access and specify which database we are going to use to provide authentication to the device. The local database on the router will do just fine for this example.
LabRouter(config)#line vty 0 4
LabRouter(config-line)#login local
LabRouter(config-line)#transport input ssh
5. You will need to create an account on the local router’s database to be used for authenticating to the device. This can be accomplished with these commands. LabRouter(config)#username XXXX privilege 15 secret XXXX
Reference: http://blog.pluralsight.com/configure-secure-shell-ssh-on-cisco-router
Q229. Refer to the exhibit.
Which statement about the device routing table is true?
A. Only networks 10.10.10.0/24 and smaller from host 192.168.168.1 are in the routing table.
B. Only networks 10.10.10.0/24 and larger from host 192.168.168.1 are in the routing table.
C. Only network 10.10.10.0/24 from host 192.168.168.1 is in the routing table.
D. Networks 10.10.10.0/24 and smaller from any host are in the routing table.
Answer: A
Explanation:
When you add the keywords “GE” and “LE” to the prefix-list, the “len” value changes its meaning. When using GE and LE, the len value specifies how many bits of the prefix you are checking, starting with the most significant bit. ip prefix-list LIST permit 1.2.3.0/24 le 32
This means: Check the first 24 bits of the prefix 1.2.3.0 The subnet mask must be less than or equal to 32
Reference: http://blog.ine.com/2007/12/26/how-do-prefix-lists-work/
Q230. Which trunking configuration between two Cisco switches can cause a security risk?
A. configuring different native VLANs on the switches
B. configuring different trunk modes on the switches
C. configuring mismatched VLANs on the trunk
D. disabling DTP on the trunk ports
E. configuring incorrect channel-groups on the switches
Answer: A