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- CCNP Switching 642-813
26.
ISL is being configured on a Company switch. Which of the following choices are true regarding
the ISL protocol? (Select two)
- A.It can be used between Cisco and non-Cisco switch devices
- B.It calculates a new CRC field on top of the existing CRC field.
- C.It adds 4 bytes of protocol-specific information to the original Ethernet frame.
- D.It adds 30 bytes of protocol-specific information to the original Ethernet frame.
- Answer & Explanation
- Report
Answer : [B, D]
Explanation :
Explanation :
| ISL adds a total of 30bytes to the Ethernet frame. A 26 byte header (10bytes identifies the VLAN ID) and a 4 byte trailer (containing a separate CRC). |
27.
You are the network administrator tasked with designing a switching solution for the Company
network. Which of the following statements describing trunk links are INCORRECT? (Select all
that apply)
- A.The trunk link belongs to a specific VLAN.
- B.Multiple trunk links are used to connect multiple end user devices
- C.A trunk link only supports native VLAN.
- D.Trunk links use 802.10 to identify a VLAN.
- E.The native VLAN of the trunk link is the VLAN that the trunk uses for untagged packets.
- Answer & Explanation
- Report
Answer : [A, B, C, D]
Explanation :
Explanation :
| A trunk is a point-to-point link that transmits and receives traffic between switches or between switches and routers. Trunks carry the traffic of multiple VLANs and can extend VLANs across an entire network. 100BaseT and Gigabit Ethernet trunks use Cisco ISL (the default protocol) or industry-standard IEEE 802.1Q to carry traffic for multiple VLANs over a single link. Frames received from users in the administratively-defined VLANs are identified or tagged for transmission to other devices. Based on rules you define, a unique identifier (the tag) is inserted in each frame header before it is forwarded. The tag is examined and understood by each device before any broadcasts or transmission to other switches, routers, or end stations. When the frame reaches the last switch or router, the tag is removed before the frame is transmitted to the target end station. |
28.
Switch R1 has been configured with the root guard feature. What statement is true if the spanning
tree enhancement Root Guard is enabled?
- A.If BPDUs are not received on a non-designated port, the port is moved into the STP loopinconsistent blocked state
- B.IF BPDUs are received on a PortFast enabled port, the port is disabled.
- C.If superior BPDUs are received on a designated port, the interface is placed into the rootinconsistent blocked state.
- D.If inferior BPDUs are received on a root port, all blocked ports become alternate paths to the root bride.
- Answer & Explanation
- Report
Answer : [C]
Explanation :
Explanation :
| Root guard is configured on a per-port basis, and does not allow the port to become a STP root port. This means that the port is always STP-designated. If there is a better BPDU received on this port, root guard will put the port into root-inconsistent STP state, rather than taking the BPDU into account and electing a new STP root. Root guard needs to be enabled on all ports where the root bridge should not appear. In a way one can configure a perimeter around part of network where STP root is allowed to be located. |
29.
On switch R1 you issue the "udld enable" global command. What does this command accomplish?
- A.Enables all fiber-optic LAN ports for Unidirectional LINK Detection (UDLD)
- B.Enables all copper media LAN ports Unidirectional Link Detection (UDLD)
- C.Overrides the default UDLS setting for all ports
- D.Globally enables all ports on the device for Unidirectional Link Detection (UDLS)
- E.None of the other alternatives apply
- Answer & Explanation
- Report
Answer : [A]
Explanation :
Explanation :
|
Enabling UDLD Globally
Beginning in privileged EXEC mode, follow these steps to enable UDLD globally on all fiber-optic
interfaces on the switch: To disable UDLD globally on fiber-optic interfaces, use the no udld enable global configuration command. |
30.
The Company network utilizes the Multiple-instance Spanning Tree protocol in its switched LAN.
Which three statements about the MST protocol (IEEE 802.1S) are true? (Select three)
- A.To verify the MST configuration, the show pending command can be used in MST configuration mode.
- B.When RSTP and MSTP are configured; UplinkFast and BackboneFast must also be enabled.
- C.All switches in the same MST region must have the same VLAN-to-instance mapping, but different configuration revision numbers.
- D.All switches in an MST region, except distribution layer switches, should have their priority lowered from the default value 32768.
- E.An MST region is a group of MST switches that appear as a single virtual bridge to adjacent CST and MST regions.
- F.Enabling MST with the "spanning-tree modemst" global configuration command also enables RSTP.
- Answer & Explanation
- Report
Answer : [A, E, F]
Explanation :
Explanation :
|
MST is built on the concept of mapping one or more VLANs to a single STP instance. Multiple
instances of STP can be used (hence the name MST), with each instance supporting a different
group of VLANs. Each could be tuned to result in a different topology, so that Instance 1 would forward on the left uplink, while Instance 2 would forward on the right uplink. Therefore, VLAN A would be mapped to Instance 1 ,and VLAN B to Instance 2. To implement MST in a network, you need to determine the following: The number of STP instances needed to support the desired topologies. Whether to map a set of VLANs to each instance. |
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