H12-821_V1.0 Practice Questions

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 ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding the IGMP Group Entry:

The IGMP group entry contains key information about multicast groups on the interface:

Group Address (225.1.1.2): The multicast group address that the user has joined.

Last Reporter (10.1.6.10): The IP address of the last host that sent an IGMP Report message for this group.

Uptime: The duration since the group was first reported.

Expires: The remaining time before the group entry ages out if no further reports are received.

2. Analysis of Each Statement:

Option A: This entry can be used to construct the corresponding (S, G) entry.

Incorrect.

This is a group entry for IGMP, which contains information about the group (G) but does not include a specific source (S). (S, G) entries are created in PIM (Protocol Independent Multicast), not IGMP.

Option B: This entry is created when the device receives an IGMP Join message from a user.

Correct.

IGMP Join messages are used by hosts to signal their intent to join a multicast group. When such a message is received, the group entry is created.

Option C: Expires indicates the aging time of the IGMP group.

Correct.

The " Expires " field shows the remaining time before the group entry ages out if no further IGMP reports are received.

Option D: 225.1.1.2 is the address of the group that the user joins.

Correct.

The " Group Address " field explicitly states that 225.1.1.2 is the multicast group that the user has joined.

3. Summary:

Correct Options: B, C, D

Comprehensive and Detailed Step-by-Step Explanation:

1. Understanding the Prefix List Configuration:

The command ip ip-prefix test index 10 permit 10.0.0.0 8 less-equal 32 defines the following:

The prefix base is 10.0.0.0 with a mask length of 8 bits.

The less-equal 32 condition allows routes with mask lengths ranging from 8 to 32 bits to match.

2. Analysis of Each Route:

Option A: 10.1.1.1/32

Correct .

The prefix 10.1.1.1/32 falls within the 10.0.0.0/8 network range and has a mask length of 32 bits, which satisfies the less-equal 32 condition.

Option B: 10.1.1.0/6

Incorrect .

The prefix 10.1.1.0/6 has a mask length of 6 bits, which is shorter than the base prefix length of 8. It does not satisfy the condition.

Option C: 10.1.1.0/24

Correct .

The prefix 10.1.1.0/24 falls within the 10.0.0.0/8 network range and has a mask length of 24 bits, which satisfies the less-equal 32 condition.

Option D: 10.0.0.0/16

Correct .

The prefix 10.0.0.0/16 falls within the 10.0.0.0/8 network range and has a mask length of 16 bits, which satisfies the less-equal 32 condition.

3. Summary:

The prefixes that match the configuration are 10.1.1.1/32, 10.1.1.0/24, and 10.0.0.0/16.

Comprehensive and Detailed In-Depth Explanation:

AS_Path is a well-known mandatory attribute (not discretionary).

AS_Path characteristics :

A.  

TRUE → When advertising to IBGP peers, AS_Path remains unchanged to prevent routing loops.

B.  

TRUE → BGP uses AS_Path to detect loops (if a router sees its own AS in the path, it rejects the route).

C.  

FALSE → AS_Path is well-known mandatory, not discretionary .

D.  

TRUE → BGP ignores AS_Confed_Sequence and AS_Confed_Set when calculating the AS_Path length.

???? Reference: Huawei HCIA-Datacom Study Guide, BGP Path Attributes and Loop Prevention.

Comprehensive and Detailed In-Depth Explanation:

In IS-IS , routes are distributed differently based on router levels :

Level-1 (L1) routers → Maintain specific routes only within their own area .

Level-2 (L2) routers → Maintain specific routes for the entire network (inter-area routing).

Level-1-2 (L1/L2) routers → Store both L1 and L2 routes and act as area border routers .

In the diagram, R2 and R3 are L1/L2 routers , meaning they store specific routes for both their area and other areas .

R1 is only an L1 router , meaning it only has intra-area routes , and R7 is an L2-only router , meaning it does not store all specific routes.

Therefore, R2 and R3 have specific routes for the entire network.

???? Reference: Huawei HCIA-Datacom Study Guide, IS-IS Routing Levels and Route Distribution.