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1. Which of the following description about the content contained in the update message is wrong?

A. Update contains reachable routing information

B. Update contains local autonomous system messages

C. Update contains information about revoking routing prefixes

D. Update includes the path attribute

Explanation: 

A. Correct. BGP update messages include reachable routing information, which informs neighboring routers about the prefixes that are reachable.

B. Incorrect. BGP update messages do not specifically contain local autonomous system messages. They may include information about the AS path, which indicates the autonomous systems the update has traversed, but not messages specific to the local AS.

C. Correct. BGP update messages can also carry withdrawal information, which indicates that certain previously advertised prefixes are no longer reachable.

D. Correct. BGP update messages include path attributes, which are critical for determining the best path to a destination. These attributes include AS path, next-hop, origin, and others.

2. Which of the following statements about stacked MAD detection is incorrect?

A. When stacking systems act as agents for each other for MAD detection, the two stacking systems can use the same Domain ID.

B. MAD detection methods are divided into direct connection detection and proxy detection.

C. MAD proxy detection requires that all stack member proxy devices are connected and the connected links are added to an Eth-Tunk.

D. MAD direct connection detection can pass through the intermediate device and can adopt full-mesh method.

Explanation: 

A. Incorrect. In a stacking scenario, each stacking system should have a unique Domain ID to avoid conflicts and ensure proper identification of each system in the network. If two stacking systems use the same Domain ID, it can lead to issues with MAD detection, causing network instability or even failures.

B. Correct. MAD detection can indeed be classified into two main methods: direct connection detection and proxy detection. Direct connection detection involves direct physical links between devices for MAD purposes, while proxy detection uses intermediary devices or proxies to assist in the MAD process.

C. Correct. In MAD proxy detection, it's essential that all stack member proxy devices are interconnected and that these connections are aggregated into an Eth-Trunk (Ethernet Trunk). This setup ensures redundancy and reliability in MAD detection.

D. Incorrect. MAD direct connection detection typically requires direct physical links between stack members and does not pass through intermediate devices. The full-mesh method involves direct connections between all stack members without intermediary devices to ensure accurate MAD detection.

3. Which of the following descriptions about BGP, OSPF, IS-IS, and RIP is correct?

A. The port number used by the BGP neighbor relationship based on the UDP session is 179

B. RIP runs on the basis of UDP sessions, and the port number used is 520

C. IS-IS runs on the basis of the IP protocol, using the protocol number 89

D. OSPF runs on the basis of the IP protocol and uses the protocol number 88

Explanation: 

A. Incorrect. BGP (Border Gateway Protocol) uses TCP (Transmission Control Protocol), not UDP. The port number for BGP is indeed 179, but it is TCP port 179, not UDP.

B. Correct. RIP (Routing Information Protocol) uses UDP (User Datagram Protocol) and operates on port number 520.

C. Incorrect. IS-IS (Intermediate System to Intermediate System) is a network layer protocol that does not use IP for its operation. Instead, it directly encapsulates its packets within Layer 2 (Data Link Layer) frames and is designed to run over the data link layer, not requiring an IP protocol number.

D. Incorrect. OSPF (Open Shortest Path First) runs over IP, but it uses protocol number 89, not 88.

4. There is an existing switch connected to a designated port through a certain port, but this port does not forward any packets, but can monitor network changes by receiving BPDUs, so which of the following options should the role of this port be?

A. Alternate port

B. Disable port

C. Root port

D. Designate port

Explanation: 

A. An Alternate port is a backup port that provides an alternate path to the root bridge. It listens for BPDUs and does not forward packets unless the active path fails. This matches the description of a port that does not forward packets but can monitor network changes by receiving BPDUs.

B. A Disabled port is one that is administratively shut down or is not participating in the Spanning Tree process. It does not send or receive BPDUs and does not forward packets. This does not match the description given in the question.

C. A Root port is the port on a non-root bridge with the lowest path cost to the root bridge. It forwards packets and actively participates in the Spanning Tree. This does not match the description as the port in question does not forward packets.

D. A Designated port is the one that has the lowest path cost on a given network segment to the root bridge. It forwards packets and participates actively in the Spanning Tree. This also does not match the description as the port in question does not forward packets.

5. Which of the following description of the virtual connection in OSPF is wrong?

A. Virtual connections can be used to solve the problem of logical discontinuity in the backbone area.

B. A virtual connection can be established on any two area border routers, but these two border routers are required

C. The virtual connection does not necessarily belong to the backbone area, and the specific districts and cities it belongs to should be determined according to the actual topology.

D. The virtual connection belongs to area 0

Explanation: 

A. Correct. Virtual links are designed to connect parts of the OSPF backbone (Area 0) that are not physically contiguous, ensuring continuity in the backbone.

B. Correct. While virtual links are indeed established between two Area Border Routers (ABRs), these ABRs must share a common non-backbone area. So, it's not just "any two" ABRs; they must have a shared area other than Area 0 to establish the virtual link.

C. Incorrect. Virtual links always belong to the backbone area (Area 0). They are used specifically to ensure the logical continuity of Area 0.

D. Correct. Virtual links are part of Area 0 and are used to maintain its logical structure even if the physical connectivity of the backbone is interrupted.

6. Regarding the basic concept of link aggregation, which of the following description is wrong?

A. Link aggregation is a method of bundling a group of physical interfaces together as a logical interface to increase bandwidth and reliability.

B. Link aggregation follows the IEE802.3ad protocol.

C. The logical link formed by bundling several physical links together is called a link aggregation group (LAG or Trunk)

D. Link aggregation only exists on active interfaces

Explanation: 

A. Correct. Link aggregation combines multiple physical network links into a single logical link, which can enhance both bandwidth and redundancy.

B. Correct. The IEEE 802.3ad standard defines link aggregation, which is now a part of the IEEE 802.1AX standard.

C. Correct. The term "Link Aggregation Group" (LAG) or "Trunk" is commonly used to refer to the logical link created by bundling multiple physical links together.

D. Incorrect. Link aggregation can include both active and standby (passive) interfaces. The purpose of having standby interfaces is to provide failover capabilities, enhancing the reliability and redundancy of the network. Not all interfaces in a link aggregation group need to be actively transmitting data at all times.

7. Which of the following descriptions of the BFD session establishment method is incorrect?

A. Static configuration of a BFD session refers to manually configuring BFD session parameters through the command line, including local identifiers, remote identifiers, etc.

B. The system distinguishes between static BFD sessions and dynamic BFD sessions by configuring local and remote identifiers.

C. When dynamically establishing a BFD session, the system will dynamically allocate a local identifier.

D. When detecting a network that uses static routing to achieve Layer 3 interoperability, BFD sessions can only be established dynamically.

Explanation: 

A. Correct. In a static configuration, the parameters such as local and remote identifiers are manually set via the command line interface (CLI).

B. Incorrect. The distinction between static and dynamic BFD sessions is not solely based on the configuration of local and remote identifiers. Static BFD sessions are manually configured, including identifiers, whereas dynamic BFD sessions involve automatic negotiation and assignment of these parameters by the system.

C. Correct. In dynamic BFD session establishment, the system automatically allocates a local identifier without manual configuration.

D. Incorrect. BFD sessions can be established both statically and dynamically in networks using static routing. Static routing does not limit BFD session establishment to dynamic methods only; static BFD sessions can also be configured manually.

8. Which of the following OSPF packets carries master-slave relationship information?

A. DD

B. LS Request

C. Hello

D. LS Update

Explanation: 

A. DD (Database Description) Packet - Correct Answer

Purpose: Used during the initial exchange of link-state information between routers.

Master-Slave Relationship: The DD packet carries master-slave relationship information. When two OSPF routers first start exchanging databases, they establish a master-slave relationship to ensure orderly exchange. One router becomes the master and the other the slave. This relationship is used to manage the exchange of Database Description packets.

B. LS Request (Link State Request) Packet

Purpose: Used by OSPF routers to request more recent or missing pieces of the link-state database from a neighbor.

Master-Slave Relationship: The LS Request packet does not carry master-slave relationship information. It is used to request specific link-state advertisements (LSAs) from another router to complete or update the local link-state database.

C. Hello Packet

Purpose: Used to establish and maintain neighbor relationships. Hello packets are sent periodically between OSPF routers to discover and maintain neighbor relationships.

Master-Slave Relationship: The Hello packet does not carry master-slave relationship information. It mainly contains information about the sending router and its OSPF parameters, such as the router ID, area ID, and Hello/dead intervals.

D. LS Update (Link State Update) Packet

Purpose: Used to distribute the LSAs to OSPF routers. LS Update packets contain a list of LSAs that are used to update the link-state database of OSPF routers.

Master-Slave Relationship: The LS Update packet does not carry master-slave relationship information. It is used to propagate LSAs to other OSPF routers.

9. Which of the following descriptions about ABR in OSPF is wrong?

A. The ABR converts Type 1 and Type 2 LSAs in the connected non-backbone area into Type 3 LSAs and advertises them to the backbone area

B. ABR cannot generate Type 4 and Type 5 LSAs

C. There are multiple LSDBs on the ABR, and the ABR maintains an LSDBD for each area.

D. ABR converts Type 1, Type 2 LSA and Type 3 LSA in the backbone area into Type 3 LSA and publishes them to the connected non-backbone area

Explanation: 

A. Correct. This statement accurately describes the function of an ABR in OSPF. The ABR summarizes and converts Type 1 (Router LSAs) and Type 2 (Network LSAs) from non-backbone areas into Type 3 LSAs (Summary LSAs) and advertises them into the backbone area (Area 0).

B. Incorrect. This statement is false. An ABR can generate Type 4 LSAs (ASBR Summary LSAs) when an Autonomous System Boundary Router (ASBR) exists in one of the non-backbone areas. Type 4 LSAs are used to inform other areas about the presence of the ASBR. Additionally, ABRs can also propagate Type 5 LSAs (AS External LSAs) originated by ASBRs into other areas.

C. Correct. This statement is true. An ABR maintains separate Link State Databases (LSDBs) for each OSPF area it is connected to, as it needs to keep track of different topologies and link-state information for each area.

D. Incorrect. This statement is false. An ABR does not convert Type 1 and Type 2 LSAs from the backbone area into Type 3 LSAs for non-backbone areas. Instead, it only summarizes and converts Type 1 and Type 2 LSAs from non-backbone areas into Type 3 LSAs for the backbone area. The ABR can, however, redistribute Type 3 LSAs (Summary LSAs) from the backbone area into non-backbone areas if necessary.

10. When routers running the OSPF protocol exchange DD messages, which of the following parameters will be used to elect the master-slave relationship?

A. IP address of the interface

B. DR priority of the interface

C. Area ID

D. Router ID

Answer: D

Explanation: 

In OSPF (Open Shortest Path First) protocol, when routers exchange Database Description (DD) messages during the process of establishing neighbor relationships, the master-slave relationship is determined by the Router ID. Therefore, the correct answer is: D. Router ID

The Router ID is a unique identifier assigned to each router in the OSPF domain. It is typically the highest IP address of any of the router's loopback interfaces, or it can be manually configured. During the OSPF neighbor adjacency process, routers exchange DD packets to synchronize their link-state databases. Within these DD packets, there's a field that includes the Router ID.

When routers exchange DD packets, they compare their own Router ID with that of the neighbor's. The router with the higher Router ID becomes the master, while the one with the lower Router ID becomes the slave. This master-slave relationship determines which router will dictate the pace and sequence of the database exchange process.