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400-101 Product Description:
Exam Number/Code: 400-101 vce
Exam name: CCIE Routing and Switching (v5.0)
n questions with full explanations
Certification: Cisco Certification
Last updated on Global synchronizing
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Q281. DRAG DROP
Drag and drop the OSPFv3 LSA type on the left to the functionality it provides on the right.
Q282. A floating static route appears in the routing table of an interface even when the interface is unusable.
Which action can you take to correct the problem?
A. Remove the permanent option from the static route.
B. Correct the administrative distance.
C. Configure the floating static route to point to another route in the routing table.
D. Correct the DHCP-provided route on the DHCP server.
Q283. In the DiffServ model, which class represents the highest priority with the highest drop probability?
AF43 — Assured forwarding, high drop probability, Class 4 DSCP, and Flash-override precedence.
Table of AF Classes and Drop Priority
Q284. Which three conditions can cause excessive unicast flooding? (Choose three.)
A. Asymmetric routing
B. Repeated TCNs
C. The use of HSRP
D. Frames sent to FFFF.FFFF.FFFF
E. MAC forwarding table overflow
F. The use of Unicast Reverse Path Forwarding
Causes of Flooding
The very cause of flooding is that destination MAC address of the packet is not in the L2 forwarding table of the switch. In this case the packet will be flooded out of all forwarding ports in its VLAN (except the port it was received on). Below case studies display most
common reasons for destination MAC address not being known to the switch.
Cause 1: Asymmetric Routing
Large amounts of flooded traffic might saturate low-bandwidth links causing network performance issues or complete connectivity outage to devices connected across such low-bandwidth links.
Cause 2: Spanning-Tree Protocol Topology Changes
Another common issue caused by flooding is Spanning-Tree Protocol (STP) Topology Change Notification (TCN). TCN is designed to correct forwarding tables after the forwarding topology has changed. This is necessary to avoid a connectivity outage, as after a topology change some destinations previously accessible via particular ports might become accessible via different ports. TCN operates by shortening the forwarding table aging time, such that if the address is not relearned, it will age out and flooding will occur. TCNs are triggered by a port that is transitioning to or from the forwarding state. After the TCN, even if the particular destination MAC address has aged out, flooding should not happen for long in most cases since the address will be relearned. The issue might arise when TCNs are occurring repeatedly with short intervals. The switches will constantly be fast-aging their forwarding tables so flooding will be nearly constant. Normally, a TCN is rare in a well-configured network. When the port on a switch goes up or down, there is eventually a TCN once the STP state of the port is changing to or from forwarding. When the port is flapping, repetitive TCNs and flooding occurs.
Cause 3: Forwarding Table Overflow
Another possible cause of flooding can be overflow of the switch forwarding table. In this case, new addresses cannot be learned and packets destined to such addresses are flooded until some space becomes available in the forwarding table. New addresses will then be learned. This is possible but rare, since most modern switches have large enough forwarding tables to accommodate MAC addresses for most designs. Forwarding table exhaustion can also be caused by an attack on the network where one host starts generating frames each sourced with different MAC address. This will tie up all the forwarding table resources. Once the forwarding tables become saturated, other traffic will be flooded because new learning cannot occur. This kind of attack can be detected by examining the switch forwarding table. Most of the MAC addresses will point to the same port or group of ports. Such attacks can be prevented by limiting the number of MAC addresses learned on untrusted ports by using the port security feature.
Q285. What is a reason to use DHCPv6 on a network that uses SLAAC?
A. To get a record of the IPs that are used by the clients
B. To push DNS and other information to the clients
C. No reason, because there is no need for DHCPv6 when using SLAAC
D. Because DHCPv6 can be used only in stateful mode with SLAAC to record the IPs of the clients
E. Because DHCPv6 can be used only in stateless mode with SLAAC to record the IPs of the clients
F. Because DHCPv6 is required to use first-hop security features on the switches
SLAAC is by far the easiest way to configure IPv6 addresses, simply because you don’t have to configure any IPv6 address. With SLAAC, a host uses the IPv6 Neighbor Discovery Protocol (NDP) to determine its IP address and default routers. Using SLAAC, a host requests and listens for Router Advertisements (RA) messages, and then taking the prefix that is advertised to form a unique address that can be used on the network. For this to work, the prefix that is advertised must advertise a prefix length of 64 bits (i.e., /64). But the most significant of Stateless Address Autoconfiguration (SLAAC) is it provided no mechanism for configuring DNS resolver information.Therefore SLACC can be used along with DHCPv6 (Stateless) to push DNS and other information to the clients.
Q286. Which option is an incorrect design consideration when deploying OSPF areas?
A. area 1 - area 0 - MPLS VPN backbone - area 0 - area 2
B. area 1 - MPLS VPN backbone - area 2
C. area 1 - MPLS VPN backbone - area 1
D. area 2 - area 0 - MPLS VPN backbone - area 1
E. area 0 - area 2 - MPLS VPN superbackbone - area 1
In the case of MPLS-VPN Backbone as The OSPF superbackbone behaves exactly like Area 0 in regular OSPF, so we cannot have two different area 0’s that are not directly connected to each other. When area 0 connects to the superbackbone, it simply becomes an extension of area 0.
Q287. Which two statements about IS-IS are true? (Choose two.)
A. The default hello interval is 10 seconds and the default hold timer is 30 seconds.
B. The hello interval can be changed on a per-interface basis with the command isis hello-multiplier.
C. Both routers need to have the same hello intervals and hold timers in order to form IS-IS neighbors.
D. Both IS-IS routers need to have the same capabilities in the hello packet in order to form neighbors.
To specify the length of time between hello packets that the Cisco IOS software sends, use the isis hello-interval command in interface configuration mode. By default, a value three times the hello interval seconds is advertised as the hold time in the hello packets sent. (Change the multiplier of 3 by specifying the isis hello-multiplier command.) With smaller hello intervals, topological changes are detected faster, but there is more routing traffic. The default is 10 seconds.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/iproute/command/reference/fiprrp_r/1rfisis.ht ml
Q288. DRAG DROP
Drag and drop Layer 2 QoS Commands on the left to the corresponding functions on the right.
Q289. Refer to the exhibit.
Which statement is true?
A. R2 is directly connected to the receiver for this group and is the winner of an assert mechanism.
B. R2 is directly connected to the receiver for this group, and it forwards the traffic onto Ethernet3/0, but it is forwarding duplicate traffic onto Ethernet3/0.
C. R2 has the A flag (Accept flag) set on Ethernet 3/0. This is fine, since the group is in BIDIR-PIM mode.
D. R2 is directly connected to the receiver for this group and is the loser of an assert mechanism.
E. The A flag is set until the SPT threshold is reached for this multicast group.
show ip mroute Field Descriptions
RPF neighbor or RPF nbr
IP address of the upstream router to the source. Tunneling indicates that this router is sending data to the RP encapsulated in register packets. The hexadecimal number in parentheses indicates to which RP it is registering. Each bit indicates a different RP if multiple RPs per group are used. If an asterisk (*) appears after the IP address in this field, the RPF neighbor has been learned through an assert.
Reference: http://www.cisco.com/c/en/us/td/docs/ios/12_2/ipmulti/command/reference/fiprmc_r/1rfmult 3.html
Q290. MPLS LDP IGP synchronization is configured on a link. The OSPF adjacency on that link is UP but MPLS LDP synchronization is not achieved. Which statement about this scenario is true?
A. The router excludes the link from its OSPF LSA type 1.
B. The router flushes its own router LSA.
C. The router advertises the link in its router LSA with max-metric.
D. The router advertises an LSA type 2 for this link, with the metric set to max-metric.
E. The router advertises the link and OSPF adjacency as it would when the synchronization is achieved.
To enable LDP-IGP Synchronization on each interface that belongs to an OSPF or IS-IS process, enter the mpls ldp sync command. If you do not want some of the interfaces to have LDP-IGP Synchronization enabled, issue the no mpls ldp igp sync command on those interfaces. If the LDP peer is reachable, the IGP waits indefinitely (by default) for synchronization to be achieved. To limit the length of time the IGP session must wait, enter the mpls ldp igp sync holddown command. If the LDP peer is not reachable, the IGP establishes the adjacency to enable the LDP session to be established. When an IGP adjacency is established on a link but LDP-IGP Synchronization is not yet achieved or is lost, the IGP advertises the max-metric on that link.