READ Free Dumps For Cisco- 400-101
| Question ID 18521 | Refer to the exhibit.
Which statement about the debug behavior of the device is true?
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| Option A | The device debugs all IP events for 172.16.129.4.
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| Option B | The device sends all debugging information for 172.16.129.4.
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| Option C | The device sends only NTP debugging information to 172.16.129.4.
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| Option D | The device sends debugging information every five seconds.
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| Correct Answer | A |
Explanation Explanation: This is an example of a conditional debug, where there is a single condition specified of IP address 172.16.129.4. So, all IP events for that address will be output in the debug.
| Question ID 18522 | Which three conditions can cause excessive unicast flooding? (Choose three.)
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| Option A | Asymmetric routing
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| Option B | Repeated TCNs
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| Option C | The use of HSRP
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| Option D | Frames sent to FFFF.FFFF.FFFF
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| Option E | MAC forwarding table overflow
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| Option F | The use of Unicast Reverse Path Forwarding
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| Correct Answer | A,B,E |
Explanation Explanation: 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.