Huawei H12-821_V1.0 Exam With Confidence Using Practice Dumps

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​​.

Comprehensive and Detailed in-depth Step-by-Step Explanation:In IS-IS, the interface cost is a metric used to determine the best path to a destination. Lower-cost paths are preferred over higher-cost paths. By default, IS-IS interface costs can range from 1 to 63.

Default Cost Range:

IS-IS allows the configuration of interface costs within the range of 1–63 by default. This range is sufficient for most networks.

Maximum Configurable Cost:

The maximum value that can be configured by default is 63. If there is a requirement for a higher cost range, the metric-style can be changed to wide, which allows the cost range to extend beyond 63.

Option A (67): Incorrect. 67 is not the maximum default value.

Option B (63): Correct. This is the maximum default cost value.

Option C (64): Incorrect. This is beyond the default range.

Option D (68): Incorrect. This is beyond the default range.

References:

Huawei HCIA-Datacom Study Guide, Chapter on "IS-IS Cost and Route Selection".

RFC 5308 – Routing IPv6 with IS-IS.

After Layer 3 roaming, the STA’s traffic is forwarded from the Foreign AP (FAP) to the Foreign AC (FAC), and then to the Home AC (HAC) before reaching the upper-layer network. This ensures that the STA remains on the same subnet without breaking existing sessions ​.