Understanding the Routing Table Entries on R4
* 0.0.0.0/0 (Default Route) is installed twice in the routing table.
* The NextHop values for the default route:
* 10.1.24.1 (GigabitEthernet0/0/1)
* 10.1.34.1 (GigabitEthernet0/0/0)
* Cost: Both routes have a metric (Cost) of 10, meaning they are equal-cost routes.
* Protocol: ISIS-L1 (Intermediate System to Intermediate System - Level 1) confirms these routes are coming from IS-IS routing.
* Flags: D (Dynamic) means these routes were dynamically learned via IS-IS.
Why is Option D Correct?
* Since both routes have the same cost (10), they are considered equal-cost default routes.
* The router will use both routes in a load-sharing fashion.
* The answer is NOT A (Four equal-cost routes) because there are only two default routes, not four.
* The answer is NOT B (One default route) because there are two default routes in the table.
* The answer is NOT C (Two default routes with different costs) because both routes have the same cost (10).
Real-World Application
* Equal-Cost Multi-Path (ECMP): The router can perform load balancing across the two equal-cost paths.
* Resilience & Redundancy: If one link fails, the other can take over without re-calculating the entire routing table.
# Reference: Huawei HCIE-Datacom Study Guide - IS-IS Routing & ECMP Load Balancing