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2021 Mar 400-101 exams

Q11. Refer to the exhibit. 

Which statement about this COS-DSCP mapping is true? 

A. The expedited forwarding DSCP is mapped to COS 3. 

B. COS 16 is mapped to DSCP 2. 

C. The default COS is mapped to DSCP 32. 

D. This mapping is the default COS-DSCP mapping on Cisco switches. 

Answer: A 

Explanation: 

Here we see that COS 3 is mapped to DSCP 46, which is the Expedited forwarding class: The Expedited Forwarding (EF) model is used to provide resources to latency (delay) sensitive real-time, interactive traffic. The EF model uses one marking -- DSCP 46. 


Q12. Which BGP feature prevents a router from installing an iBGP learned route in its routing table until the route is validated within the IGP? 

A. confederation 

B. aggregation 

C. advertise-map 

D. synchronization 

Answer: B 


Q13. Which technology facilitates neighbor IP address resolution in DMVPN? 

A. CEF 

B. mGRE 

C. a dynamic routing protocol 

D. NHRP 

Answer: D 

Explanation: 

NHRP Used with a DMVPN 

NHRP is used to facilitate building a VPN and provides address resolution in DMVPN. In this context, a VPN consists of a virtual Layer 3 network that is built on top of an actual Layer 3 network. The topology you use over the VPN is largely independent of the underlying network, and the protocols you run over it are completely independent of it. The VPN network (DMVPN) is based on GRE IP logical tunnels that can be protected by adding in IPsec to encrypt the GRE IP tunnels. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_4/ip_addr/configuration/guide/hadnhrp.html#w p1057255 


Q14. 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. 


Q15. Which two statements about the default behavior of IS-IS are true? (Choose two.) 

A. The default IS-IS router type is L1/L2. 

B. The default IS-IS metric type is wide. 

C. The default IS-IS interface circuit type is L1/L2. 

D. By default, two IS-IS routers must use the same hello interval and hold timer in order to become neighbors. 

Answer: A,C 


Replace 400-101 torrent:

Q16. Like OSPFv2, OSPFv3 supports virtual links. Which two statements are true about the IPv6 address of a virtual neighbor? (Choose two.) 

A. It is the link-local address, and it is discovered by examining the hello packets received from the virtual neighbor. 

B. It is the link-local address, and it is discovered by examining link LSA received by the virtual neighbor. 

C. It is the global scope address, and it is discovered by examining the router LSAs received by the virtual neighbor. 

D. Only prefixes with the LA-bit not set can be used as a virtual neighbor address. 

E. It is the global scope address, and it is discovered by examining the intra-area-prefix-LSAs received by the virtual neighbor. 

F. Only prefixes with the LA-bit set can be used as a virtual neighbor address. 

Answer: E,F 

Explanation: 

OSPF for IPv6 assumes that each router has been assigned link-local unicast addresses on each of the router's attached physical links. On all OSPF interfaces except virtual links, OSPF packets are sent using the interface's associated link-local unicast address as the source address. A router learns the link-local addresses of all other routers attached to its links and uses these addresses as next-hop information during packet forwarding. On virtual links, a global scope IPv6 address MUST be used as the source address for OSPF protocol packets. The collection of intra-area-prefix-LSAs originated by the virtual neighbor is examined, with the virtual neighbor's IP address being set to the first prefix encountered with the LA-bit set. 

Reference: https://tools.ietf.org/html/rfc5340 


Q17. An NSSA area has two ABRs connected to Area 0. Which statement is true? 

A. Both ABRs translate Type-7 LSAs to Type-5 LSAs. 

B. The ABR with the highest router ID translates Type-7 LSAs to Type-5 LSAs. 

C. Both ABRs forward Type-5 LSAs from the NSSA area to backbone area. 

D. No LSA translation is needed. 

Answer: B 


Q18. Which two statements about OSPF route types are true? (Choose two.) 

A. The cost of an external type 2 route is the sum of the external and internal costs. 

B. The cost of an external type 2 route is the same as the external cost. 

C. Intra-area routes originate outside of their area. 

D. Inter-area routes originate inside their area. 

E. The cost of an external type 1 route is the same as the internal cost. 

F. For routes to the same destination, external type 1 routes are preferred over external type 2 routes. 

Answer: B,F 

Explanation: 

External routes fall under two categories, external type 1 and external type 2. The difference between the two is in the way the cost (metric) of the route is being calculated. The cost of a type 2 route is always the external cost, irrespective of the interior cost to reach that route. A type 1 cost is the addition of the external cost and the internal cost used to reach that route. A type 1 route is always preferred over a type 2 route for the same destination. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/open-shortest-path-first-ospf/7039-1.html 


Q19. Which two statements about packet fragmentation on an IPv6 network are true? (Choose two.) 

A. The fragment header is 64 bits long. 

B. The identification field is 32 bits long. 

C. The fragment header is 32 bits long. 

D. The identification field is 64 bits long. 

E. The MTU must be a minimum of 1280 bytes. 

F. The fragment header is 48 bits long. 

Answer: A,B 

Explanation: 

The fragment header is shown below, being 64 bits total with a 32 bit identification field: 

Reference: http://www.openwall.com/presentations/IPv6/img24.html 


Q20. Which authentication method does OSPFv3 use to secure communication between neighbors? 

A. plaintext 

B. MD5 HMAC 

C. PKI 

D. IPSec 

Answer: D 

Explanation: 

In order to ensure that OSPFv3 packets are not altered and re-sent to the device, causing the device to behave in a way not desired by its system administrators, OSPFv3 packets must be authenticated. OSPFv3 uses the IPsec secure socket API to add authentication to OSPFv3 packets. This API supports IPv6. OSPFv3 requires the use of IPsec to enable authentication. Crypto images are required to use authentication, because only crypto images include the IPsec API needed for use with OSPFv3. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-sy/iro-15-sy-book/ip6-route-ospfv3-auth-ipsec.html