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2017 Mar 400-101 question

Q491. Refer to the exhibit. 

This is the configuration of the ASBR of area 110.Which option explains why the remote ABR should not translate the type 7 LSA for the prefix 192.168.0.0/16 into a type 5 LSA? 

A. The remote ABR translates all type 7 LSA into type 5 LSA, regardless of any option configured in the ASBR. 

B. The ASBR sets the forwarding address to 0.0.0.0 which instructs the ABR not to translate the LSA into a type 5 LSA. 

C. The ASBR originates a type 7 LSA with age equal to MAXAGE 3600. 

D. The ABR clears the P bit in the header of the type 7 LSA for 192.168.0.0/16. 

Answer:

Explanation: 

When external routing information is imported into an NSSA, LSA Type 7 is generated by the ASBR and it is flooded within that area only. To further distribute the external information, type 7 LSA is translated into type 5 LSA at the NSSA border. The P-bit in LSA Type 7 field indicates whether the type 7 LSA should be translated. This P-bit is automatically set by the NSSA ABR (also the Forwarding Address (FA) is copied from Type 7 LSA). The P-bit is not set only when the NSSA ASBR and NSSA ABR are the same router for the area. If bit P = 0, then the NSSA ABR must not translate this LSA into Type 5. 

The nssa-only keyword instructs the device to instigate Type-7 LSA with cleared P-bit, thereby, preventing LSA translation to Type 5 on NSSA ABR device. 

Note. If a router is attached to another AS and is also an NSSA ABR, it may originate a both a type-5 and a type-7 LSA for the same network. The type-5 LSA will be flooded to the backbone and the type-7 will be flooded into the NSSA. If this is the case, the P-bit must be reset (P=0) in the type-7 LSA so the type-7 LSA isn’t again translated into a type-5 LSA by another NSSA ABR. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/iproute_ospf/configuration/15-e/iro-15-e-book/iro-ospfv3-nssa-cfg.html 


Q492. Refer to the exhibit. 

How many EIGRP routes will appear in the routing table of R2? 

A. 0 

B. 1 

C. 2 

D. 3 

Answer:

Explanation: 

EIGRPv6 on R2 was shut down so there is no EIGRP routes on the routing table of R2. If we turn on EIGRPv6 on R2 (with “no shutdown” command) then we would see the prefix of the loopback interface of R1 in the routing table of R2. 

Note. EIGRPv6 requires the “ipv6 unicast-routing” global command to be turned on first or it will not work. 


Q493. Which two options are advantages of NetFlow version 9 over NetFlow version 5? (Choose two.) 

A. NetFlow version 9 adds support for IPv6 headers. 

B. NetFlow version 9 adds support for MPLS labels. 

C. NetFlow version 9 adds support for the Type of Service field. 

D. NetFlow version 9 adds support for ICMP types and codes. 

Answer: A,B 

Explanation: 

NetFlow version 9 includes support for all of these fields that version 5 supports and can optionally include additional information such as Multiprotocol Label Switching (MPLS) labels and IPv6 addresses and ports. 


Q494. What is the cause of ignores and overruns on an interface, when the overall traffic rate of the interface is low? 

A. a hardware failure of the interface 

B. a software bug 

C. a bad cable 

D. microbursts of traffic 

Answer:

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). You will never see a sustained data traffic within show interface’s “input rate” counter as they are averaging bits per second (bps) over 5 minutes by default (way too long to account for microbursts). You can understand microbursts from a scenario where a 3-lane highway merging into a single lane at rush hour – the capacity burst cannot exceed the total available bandwidth (i.e. single lane), but it can saturate it for a period of time. 

Reference: http://ccieordie.com/?tag=micro-burst 


Rebirth 400-101 free draindumps:

Q495. What is the purpose of Route Target Constraint? 

A. to avoid using route reflectors in MPLS VPN networks 

B. to avoid using multiple route distinguishers per VPN in MPLS VPN networks 

C. to be able to implement VPLS with BGP signaling 

D. to avoid sending unnecessary BGP VPNv4 or VPNv6 updates to the PE router 

E. to avoid BGP having to perform route refreshes 

Answer:

Explanation: 

Some service providers have a very large number of routing updates being sent from RRs to PEs, using considerable resources. A PE does not need routing updates for VRFs that are not on the PE; therefore, the PE determines that many routing updates it receives are “unwanted.” The PE can filter out the unwanted updates using Route Target Constraint. 

Reference: http://www.cisco.com/c/en/us/td/docs/ios/ios_xe/iproute_bgp/configuration/guide/2_xe/irg_x e_book/irg_rt_filter_xe.html. 


Q496. What are the three variants of NTPv4? (Choose three.) 

A. client/server 

B. broadcast 

C. symmetric 

D. multicast 

E. asymmetric 

F. unicast 

Answer: A,B,C 


Q497. Refer to the exhibit. 

If a console port is configured as shown, which response is displayed when you connect to the console port? 

A. a blinking cursor 

B. the message "Authorized users only" 

C. the username prompt 

D. three username name prompts followed by a timeout message 

E. the message "Connection refused" 

Answer:


Q498. Which two mechanisms can be used to eliminate Cisco Express Forwarding polarization? (Choose two.) 

A. alternating cost links 

B. the unique-ID/universal-ID algorithm 

C. Cisco Express Forwarding antipolarization 

D. different hashing inputs at each layer of the network 

Answer: B,D 

Explanation: 

This document describes how Cisco Express Forwarding (CEF) polarization can cause suboptimal use of redundant paths to a destination network. CEF polarization is the effect when a hash algorithm chooses a particular path and the redundant paths remain completely unused. 

How to Avoid CEF Polarization 

. Alternate between default (SIP and DIP) and full (SIP + DIP + Layer4 ports) hashing inputs configuration at each layer of the network. 

. Alternate between an even and odd number of ECMP links at each layer of the network.The CEF load-balancing does not depend on how the protocol routes are inserted in the routing table. Therefore, the OSPF routes exhibit the same behavior as EIGRP. In a hierarchical network where there are several routers that perform load-sharing in a row, they all use same algorithm to load-share. 

The hash algorithm load-balances this way by default: 

1: 1 

2: 7-8 

3: 1-1-1 

4: 1-1-1-2 

5: 1-1-1-1-1 

6: 1-2-2-2-2-2 

7: 1-1-1-1-1-1-1 

8: 1-1-1-2-2-2-2-2 

The number before the colon represents the number of equal-cost paths. The number after the colon represents the proportion of traffic which is forwarded per path. 

This means that: 

For two equal cost paths, load-sharing is 46.666%-53.333%, not 50%-50%. 

For three equal cost paths, load-sharing is 33.33%-33.33%-33.33% (as expected). 

For four equal cost paths, load-sharing is 20%-20%-20%-40% and not 25%-25%-25%-25%. 

This illustrates that, when there is even number of ECMP links, the traffic is not load-balanced. 

.Cisco IOS introduced a concept called unique-ID/universal-ID which helps avoid CEF polarization. This algorithm, called the universal algorithm (the default in current Cisco IOS versions), adds a 32-bit router-specific value to the hash function (called the universal ID - this is a randomly generated value at the time of the switch boot up that can can be manually controlled). This seeds the hash function on each router with a unique ID, which ensures that the same source/destination pair hash into a different value on different routers along the path. This process provides a better network-wide load-sharing and circumvents the polarization issue. This unique -ID concept does not work for an even number of equal-cost paths due to a hardware limitation, but it works perfectly for an odd number of equal-cost paths. In order to overcome this problem, Cisco IOS adds one link to the hardware adjacency table when there is an even number of equal-cost paths in order to make the system believe that there is an odd number of equal-cost links. 

Reference: http://www.cisco.com/c/en/us/support/docs/ip/express-forwarding-cef/116376-technote-cef-00.html 


Q499. 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:

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.