In an HPE Aruba Networking AOS-8 architecture with a Mobility Master (MM), Mobility Controllers (MCs), and campus APs (CAPs), the WLAN is configured to use Tunnel forwarding mode and WPA3-Enterprise security. In Tunnel mode, all user traffic from the APs is encapsulated in a GRE tunnel and sent to the MC, which then forwards the traffic to the appropriate VLAN. The WLAN is assigned to VLAN 301, and the core routing switches act as the default router for wireless user traffic.

Tunnel Forwarding Mode: In this mode, the AP does not directly place user traffic onto the wired network. Instead, the AP tunnels all user traffic to the MC over a GRE tunnel. The MC then decapsulates the traffic and places it onto the wired network in the specified VLAN (VLAN 301 in this case). This means the VLAN tagging for user traffic occurs at the MC, not at the AP.

VLAN 301 Assignment: Since the WLAN is assigned to VLAN 301, the MC will tag user traffic with VLAN 301 when forwarding it to the wired network. The core routing switches, acting as the default router, need to receive this traffic on VLAN 301 to route it appropriately.

Therefore, VLAN 301 needs to be carried on the links between the MC ports and the core routing switches, as this is where the MC forwards the user traffic after decapsulating it from the GRE tunnel.

Option A, "Only links on the path between APs and the core routing switches," is incorrect because, in Tunnel mode, the APs do not directly forward user traffic to the wired network. The traffic is tunneled to the MC, so the links between the APs and the core switches do not need to carry VLAN 301 for user traffic (though they may carry other VLANs for AP management).

Option B, "Only links on the path between APs and the MC," is incorrect for the same reason. The GRE tunnel between the AP and MC carries encapsulated user traffic, and VLAN 301 tagging occurs at the MC, not on the AP-to-MC link.

Option C, "All links in the campus LAN to ensure seamless roaming," is incorrect because VLAN 301 only needs to be present where the MC forwards user traffic to the wired network (i.e., between the MC and the core switches). Extending VLAN 301 to all links is unnecessary and could introduce security or scalability issues.

Option D, "Only links between MC ports and the core routing switches," is correct because the MC places user traffic onto VLAN 301 and forwards it to the core switches, which act as the default router.

The HPE Aruba Networking AOS-8 8.11 User Guide states:

"In Tunnel forwarding mode, the AP encapsulates all user traffic in a GRE tunnel and sends it to the Mobility Controller (MC). The MC decapsulates the traffic and forwards it to the wired network on the VLAN assigned to the WLAN. For example, if the WLAN is assigned to VLAN 301, the MC tags the user traffic with VLAN 301 and sends it out of its wired interface to the upstream switch. Therefore, the VLAN must be configured on the links between the MC and the upstream switch or router that acts as the default gateway for the VLAN." (Page 275, Tunnel Forwarding Mode Section)

Additionally, the HPE Aruba Networking Wireless LAN Design Guide notes:

"When using Tunnel mode, the VLAN assigned to the WLAN must be carried on the wired links between the Mobility Controller and the default router for the VLAN. The links between the APs and the MC do not need to carry the user VLAN, as all traffic is tunneled to the MC, which handles VLAN tagging." (Page 52, VLAN Configuration Section)