Huawei H12-821_V1.0 Practice Test - Questions Answers, Page 4

ACL Matching in Huawei Routers:

Access Control Lists (ACLs) are used to filter packets based on specific criteria, such as source/destination IP, ports, or protocols.

When a packet arrives, the Huawei router processes it against the configured ACL rules to decide whether to permit or deny the packet.

Sequential Matching Order:

By default, Huawei routers match packets against ACL rules sequentially. This means:

The router checks the packet against rules in the order they are listed, starting from the top of the ACL.

The first rule that matches the packet's attributes is applied, and no further rules are checked. This is known as the first-match principle.

If no rules match, the packet is denied by default (implicit deny).

Example of Sequential Matching:

Consider the following ACL rules:

Rule 10: Permit IP 192.168.1.0/24

Rule 20: Deny IP 192.168.1.1

If a packet with source IP 192.168.1.1 arrives:

The router matches it against Rule 10 (Permit 192.168.1.0/24) and allows the packet.

Rule 20 is not evaluated because the first match (Rule 10) already applies.

Alternative Matching Orders:

Some routers or configurations allow batch matching (evaluating all rules) for specific scenarios, but this is not the default behavior in Huawei routers.

Conclusion:

The default ACL matching order on Huawei routers is sequential, and the first matching rule determines the action applied to the packet.

RPC (Root Path Cost) Comparison:

Once the root bridge is selected, the network needs to determine the best path to the root. Each port on a non-root bridge will calculate the Root Path Cost (RPC), which is the cumulative cost of reaching the root bridge from that port. The root port is the one that has the lowest RPC, meaning it provides the best path to the root bridge.

Peer BID Comparison:

If multiple paths have the same Root Path Cost, the next step is to compare the Peer Bridge IDs. The bridge with the lowest Peer BID is chosen as the root port. This ensures a tie-breaking mechanism based on the neighbor's identifier.

Local BID Comparison:

If there is still a tie after comparing the Peer Bridge IDs, the Local Bridge ID is compared. A smaller Local BID indicates a higher priority, and the port with the lower Local BID will be selected as the root port.

Additional Port Roles in MSTP

Master Port: Indicates the port on the shortest path to the root bridge in a region.

Regional Edge Port: Identifies a port at the boundary of the MST region.

Backup and edge ports exist in RSTP and are not newly introduced by MSTP.

HCIP-Datacom-Core Reference

MSTP port roles are elaborated in the MSTP configuration sections.

RST BPDU Handling

On an RSTP network, if a port receives an RST BPDU and determines its own buffered BPDU is superior, it discards the received BPDU without responding. This ensures stability and proper convergence in the network.

HCIP-Datacom-Core Reference

BPDU handling is described in the RSTP operation chapters.

Edge Port Behavior

An edge port transitions directly to the Forwarding state but reverts to participating in RSTP calculations if it receives a valid configuration BPDU. Thus, statement C is false.

HCIP-Datacom-Core Reference

The behavior of edge ports and their transitions are discussed in the RSTP enhancement sections.

Permanent Group Addresses for Routing Protocols

The range 224.0.0.0 to 224.0.0.255 is reserved for local network protocols, including routing protocols. Examples include OSPF (224.0.0.5/6) and RIP (224.0.0.9).

HCIP-Datacom-Core Reference

Reserved multicast address ranges are detailed in the multicast configuration sections.

GMP Snooping Proxy

IGMP snooping proxy allows the switch to substitute for upstream Layer 3 devices and downstream hosts, reducing unnecessary bandwidth consumption by consolidating IGMP messages.

HCIP-Datacom-Core Reference

The IGMP snooping proxy functionality is described in multicast optimization and IGMP configuration chapters

Routing Entries in PIM

(S, G) entries: Represent the shortest path tree (SPT) from a specific source (S) to a specific multicast group (G). These entries are created after data packets are transmitted directly from the source to the receivers.

(S, G) entries are used in both PIM-DM and PIM-SM modes.

PIM-DM and PIM-SM Modes

In PIM-DM, multicast traffic is initially flooded throughout the network and pruned where no receivers exist. (S, G) entries represent source-specific paths created after the flooding stage.

In PIM-SM, multicast traffic initially flows through a shared tree, but (S, G) entries are created when the network switches to the SPT for more efficient forwarding.

HCIP-Datacom-Core Reference

The functionality and application of (S, G) routing entries are detailed in multicast and PIM configuration chapters.

PIM (Protocol Independent Multicast):

PIM is a routing protocol designed for efficient routing of IP multicast traffic. It determines the paths over which multicast packets should be forwarded.

PIM is 'protocol-independent' because it uses the underlying unicast routing table for RPF (Reverse Path Forwarding) checks.

It is responsible for distributing multicast data throughout the network.

IGMP Snooping:

IGMP Snooping operates at Layer 2 and monitors IGMP traffic between hosts and routers.

It prevents multicast flooding by allowing a switch to forward multicast packets only to the ports that have joined specific multicast groups.

This significantly enhances efficiency in Layer 2 networks with multicast traffic.