Which of the following answer choices are correct characteri

正确答案：ACF
A,C,F 解析：Explanation:
The main function of a router is to connect different, separated networks together. In doing so, switching packets from one network to another is a primary function, along with providing for communication between networks. As an additional feature, routers are capable of providing filtering on a network address and application port level, so choice C is also correct.

Incorrect Answers:
B. Routers can indeed be used to segment a network separate a collision domain, since routers do not forward LAN broadcasts and multicasts to other interfaces. However, routers alone can not prevent all collisions from occurring on any given LAN segment.

D. Routers actually segment LANs into smaller broadcast domains.

E. Routers do not forward broadcast and multicast traffic out the additional interfaces by default. Unless bridging or IP helpers are configured on the router, LAN broadcasts are blocked at the router level.

参考答案:C

正确答案：BCE
B,C,E 解析：Explanation:
The application layer is the highest OSI layer, and protocols at this layer are end-user oriented. HTTPS so people can get information on the internet, SMTP so people can manage networks, and TFTP so people can download files.

Incorrect Answers:
A, D, F. ARP, CDP, ICMP are protocols that equipment like routers and switches use to communicate with themselves, and belong to lower levels on the model.

参考答案：A, C, D

参考答案：B, C

正确答案：BD
B,D 解析：Explanation:
Trunks are used to carry traffic belonging to multiple VLANs between devices over the same link. A device can determine which VLAN the traffic belongs to by its VLAN identifier. The VLAN identifier is a tag that is encapsulated with the data. ISL and 802.1q are two types of encapsulations used to carry data from multiple VLANs over trunk links.

ISL is a Cisco proprietary protocol for interconnecting multiple switches and maintaining VLAN information as traffic goes between switches. ISL provides VLAN trunking capabilities while maintaining full wire speed performance on Ethernet links in full-duplex or half-duplex mode. ISL operates in a point-to-point environment and will support up to 1000 VLANs.

In ISL, the original frame. is encapsulated and an additional header is added before the frame. is carried over a trunk link. At the receiving end, the header is removed and the frame. is forwarded to the assigned VLAN. .ISL uses Per VLAN Spanning Tree (PVST) which runs one instance of Spanning Tree Protocol (STP) per VLAN.

PVST allows for optimal root switch placement for each VLAN and supports load balancing of VLANs over multiple trunk links. 802.1Q is the IEEE standard for tagging frames on a trunk and supports up to 4096 VLANs. In 802.1Q, the trunking device inserts a four-byte tag into the original frame. and re-computes the Frame. Check Sequence (FCS) before sending the frame. over the trunk link. At the receiving end, the tag is removed and the frame. is forwarded to the assigned VLAN. 802.1Q does not tag frames on the native VLAN.

It tags all other frames transmitted and received on the trunk. While configuring a 802.1 trunk, you must make sure that the same native VLAN is configured on both sides of the trunk. IEEE 802.1Q defines a single instance of spanning tree running on the native VLAN for all the VLANs in the network which is called Mono Spanning Tree (MST). This lacks the flexibility and load balancing capability of PVST available with ISL. However, PVST+ offers the capability to retain multiple Spanning Tree topologies with 802.1Q trunking.

正确答案：CE
C,E 解析：Explanation:
The bridges elect a root bridge based on the bridge IDs in the BPDUs. The root bridge is the bridge with the lowest numeric value for the bridge ID. Because the two part bridge ID starts with the priority value, essentially the bridge with the lowest priority becomes the root.

For instance, if one bridge has priority 100, and another bridge has priority 200, the bridge with priority 100 wins, regardless of what MAC address was used to create the bridge ID or each bridge/switch.

正确答案：BD
B,D 解析：Explanation:
ISL and 802.1Q are the two trunking encapsulations that can be configured on a Cisco switch. ISL is Cisco proprietary and 802.1Q is the IEEE standard method.

Incorrect Answers:
A. VTP is the VLAN Trunking Protocol, which is used to carry VLAN information across the trunks. The question is asking for the encapsulation options for the trunk, which will be used by VTP.

C. LLC is the Logical Link Control, which is a sub-layer of the data link layer.

E. CDP is the Cisco Discovery Protocol, which is used by Cisco devices to discover information on neighboring Cisco devices.

F. PAP is the Password Authentication Protocol, which is used as an authentication mechanism on PPP links.

参考答案：D