Huawei Updated H12-821_V1.0 Exam Questions and Answers by mimi

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Explanation of Root Port Election in STP:

In a Spanning Tree Protocol (STP) network, theRoot Portis selected on each switch (except the Root Bridge). The Root Port is the port with thelowest path costto the Root Bridge. If there is a tie in path cost, the following criteria are used in sequence to break the tie:

Steps for Root Port Election in Sequence:

RPC Comparison (Root Path Cost):

The port with thelowest Root Path Costis preferred.

Root Path Cost is the cumulative cost of the path to the Root Bridge.

Peer BID (Bridge ID) Comparison:

If the Root Path Costs are equal, theBridge IDof the connected switch (peer) is compared.

The port connecting to the switch with thelower Bridge IDis preferred.

Peer PID (Port ID) Comparison:

If the Bridge IDs are equal, thePort IDof the peer's sending port is compared.

The port connecting to thelower Port IDis preferred.

Local PID (Port ID) Comparison:

If all else is equal, theLocal Port IDof the switch is used.

The port with thelower Local Port IDis selected.

Root protection ensures that a designated port does not become a root port by discarding superior BPDUs. However, if superior BPDUs are no longer received, the port can return to its original forwarding state, meaning its role can change. This makes option B incorrect, while the other options correctly describe RSTP behavior ​.

Comprehensive and Detailed Step-by-Step Explanation:

1. Single-Hop BFD Session:

A single-hop BFD session is used to detect link failures between directly connected devices.

It is bound to thelocal IP addressand thepeer IP address, and the session relies on these parameters to establish connectivity.

2. Why Modifications Require Deletion:

BFD sessions are tightly bound to their configuration parameters (e.g., local and peer IP addresses).

Modifying these parameters is not supported for an existing session. Instead, you must delete the session and recreate it with the updated parameters.

3. Why the Statement is TRUE:

The statement correctly describes the behavior of BFD sessions, where modifying an existing session is not possible without deleting it first.

1 → A Startup message with a priority of 255 is received.

2 → A Startup message with a priority less than 255 is received.

3 → A Shutdown message is received.

4 → The Master_Down timer expires, an Advertisement packet with the priority of 0 is received, or a packet with a priority lower than the local priority is received.

5 → A packet with a priority higher than the local priority is received.

6 → A Shutdown message is received.

????Reference:Huawei HCIA-Datacom Study Guide, VRRP Status Transitions.