Refer to the exhibit. This customer uses Gigabit Ethernet on all router interfaces and gets point- to-point Layer 2 VPN connections from their telco provider. This network runs IS-IS with default…

Manually adjusting interface metrics would technically achieve path preference, but it requires per-interface manual configuration rather than using bandwidth-aware automatic calculation that correctly reflects circuit speed across all interfaces.

Matching the interface bandwidth to actual circuit speed updates the bandwidth descriptor on the interface, but IS-IS does not automatically derive its routing metric from the interface bandwidth value without also configuring bandwidth-based metric calculation via the reference bandwidth.

IS-IS with default parameters assigns a fixed metric of 10 to every interface regardless of actual bandwidth, so high-speed Gigabit links and lower-speed Layer 2 VPN circuits appear equally preferred. Adjusting the reference bandwidth parameter enables IS-IS to automatically compute interface metrics inversely proportional to link speed, resulting in lower metrics on true Gigabit interfaces and higher metrics on slower VPN circuits, steering router A traffic onto the high-speed path toward router H.

Adjusting delay parameters affects metrics in protocols like EIGRP that incorporate delay into a composite metric; IS-IS does not use delay as an input to its metric calculation and changing delay values has no effect on IS-IS path selection.