Comprehensive and Detailed In-Depth Explanation:
* A NET (Network Entity Title) consists of three parts:
* Area Address # Identifies the IS-IS area.
* System ID # Uniquely identifies the router.
* SEL (NSEL - N-selector) # Always 0 in IS-IS.
* The Area Address part contains:
* AFI (Authority and Format Identifier) # Identifies the address type.
* IDI (Initial Domain Identifier) # Identifies the routing domain.
* System ID is NOT part of the Area Address, so the correct answers are B (AFI) and C (IDI).
# Reference: Huawei HCIA-Datacom Study Guide, IS-IS Addressing and NET Structure.

Comprehensive and Detailed in-depth Step-by-Step Explanation:
In an Intermediate System to Intermediate System (IS-IS) network, aDesignated Intermediate System (DIS)is elected on broadcast networks to perform the following functions:
Represent the broadcast network as a pseudonode.
Generate and update the Link State Protocol Data Units (LSPs) for the pseudonode.
The DIS is elected based on theDIS priorityvalue, which is configured on IS-IS interfaces. If two routers have the same priority, the router with the higher MAC address becomes the DIS.
Thedefault DIS priorityfor IS-IS interfaces is64, which can be modified depending on the network requirements.
Option A (200):Incorrect. This is not the default value.
Option B (64):Correct. This is the default DIS priority value.
Option C (1):Incorrect. This is not the default value.
Option D (100):Incorrect. This is not the default value.
References:
Huawei HCIA-Datacom Study Guide, Chapter on "IS-IS Basics".
RFC 1195 - Use of OSI IS-IS for Routing in TCP/IP and Dual Environments.

High-availability Stateful Backup (HSB) ensures synchronization between active and standby devices. If the HSB channel fails to establish, the following causes are possible:
* TCP channel not established: The HSB channel relies on a TCP connection. If the TCP session cannot be established, the backup process cannot start.
* Mismatched retransmission settings: If the retransmission count and interval for HSB service packets are inconsistent between the two devices, the synchronization process fails.
* Incorrect source and destination configurations: If the source IP address and port number on one device do not match the destination IP address and port number on the other, the channel cannot be established.
Option C is incorrect because the priority of the two ACs affects active/standby roles but does not directly impact HSB channel establishment .

Explanation:
Network Types and Corresponding Link Layer Protocols
* Broadcast: Ethernet
* Point-to-Point (P2P): PPP, HDLC
* Point-to-Multipoint (P2MP): PPP
* Non-Broadcast Multi-Access (NBMA): Frame Relay
OSPF Network Types:OSPF classifies networks based on link layer protocols into the following types:
* Broadcast: This type assumes that all routers on the network can communicate directly with one another using multicast or broadcast frames. Ethernet networks are typical examples.
* Point-to-Point (P2P): This type is used for links that connect two routers directly. Common protocols include PPP (Point-to-Point Protocol) and HDLC.
* Point-to-Multipoint (P2MP): This type simulates multiple point-to-point connections over a single physical network, often used in WAN scenarios where PPP is employed.
* Non-Broadcast Multi-Access (NBMA): These networks connect multiple devices but lack native broadcast capability, such as Frame Relay.

Explanation:
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