H12-821_V1.0 Practice Questions

The LS age field in OSPF LSAs (Link State Advertisements) is measured in seconds and increments over time in the Link State Database (LSDB). If the LS age reaches the LSRefreshTime (30 minutes), the router that originated the LSA must regenerate it to keep the LSA valid in the network. Options C and B are incorrect since LS age does not decrease, and only the originator regenerates LSAs ​.

Explanation of VLAN Pool Assignment Algorithms:

In WLANs,VLAN poolshelp reduce broadcast domains and improve network performance by distributing users across multiple VLANs. Two algorithms are used for VLAN assignment:

Even Assignment Algorithm:

The number of users in each VLAN is even.

This algorithm assigns users evenly across VLANs, ensuring a balanced distribution of users in each VLAN.

When STAs go offline and online again, their VLANs and IP addresses may easily change.

Since the assignment is based on maintaining even distribution, a device (STA) may not be assigned the same VLAN when it reconnects, leading to potential IP address changes.

Hash Assignment Algorithm:

The number of users in each VLAN is uneven.

The hash algorithm assigns users to VLANs based on a hash value (e.g., derived from the MAC address). This may result in an uneven distribution of users across VLANs.

VLANs and IP addresses remain unchanged for STAs that go offline and online again.

The hash algorithm ensures that a device reconnects to the same VLAN, preserving its IP address.

A screenshot of a computer Description automatically generated

In PIM-DM (Protocol Independent Multicast - Dense Mode), the SPT (Shortest Path Tree) establishment process involves flooding to propagate multicast traffic across the network, prune messages to stop sending multicast traffic to unwanted interfaces, and graft messages to re-establishforwarding when needed. State-refresh is not directly involved in SPT establishment but helps maintain the prune state ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. What is the BFD Echo Function?

BFD (Bidirectional Forwarding Detection) is used to detect link failures.

TheEcho functionis an optional feature that tests link connectivity by looping back packets sent from the local device through the forwarding path.

2. Analysis of Each Statement:

Option A: If URPF is enabled on the peer end, BFD packets may be incorrectly discarded on the peer end.

Correct.

URPF (Unicast Reverse Path Forwarding) checks whether the source IP address of an incoming packet is reachable via the interface it was received on. Since the Echo function uses loopback packets, this can conflict with URPF, causing the packets to be dropped.

Option B: In the BFD Echo function, the device uses the IP address of the outbound interface as the source IP address by default.

Correct.

By default, the outbound interface's IP address is used as the source address for BFD Echo packets.

Option C: The BFD Echo function applies only to single-hop BFD sessions.

Incorrect.

The BFD Echo function can be used for both single-hop and multi-hop BFD sessions.

Option D: When configuring a BFD session supporting the BFD Echo function, you need to configure both the local and remote discriminators.

Incorrect.

The BFD Echo function is locally configured and does not require setting remote discriminators. The function operates independently of the remote device's configuration.

3. Summary:

The correct statements areAand

B.