The root cause is the incorrect scoping of the static default route on the Active/Active Tier-0 Gateway. The symptom, "Get route shows the default route present only on VLAN 100 interface (fp-eth0), missing on VLAN 101 (fp-eth1)," directly confirms that the route's scope has been limited to the VLAN 100 uplink. In this configuration, the BGP process attempting to establish a session with the peer on the VLAN 101 subnet (192.168.101.1) fails because it cannot find a suitable default route on its associated interface (fp-eth1). This leads to the "No route to peer" error, causing the BGP session to remain in the Idle state, even though basic IP connectivity (ping) is functional.

B. The ability to successfully ping the ToR routers from the Edge nodes confirms that bidirectional routing is working correctly; therefore, the ToRs have the necessary routes back.

C. eBGP multi-hop is used when BGP peers are not in the same subnet (not directly connected). Here, the Tier-0 uplinks are directly connected to the ToR routers.

D. A BGP authentication mismatch would cause the session to fail after the TCP connection is established, typically resulting in BGP notification messages, not a "No route to peer" error.

1. VMware NSX-T Data Center Administration Guide (NSX 3.2, Page 168): In the section "Add a Static Route on a Tier-0 Gateway," the guide describes the "Set Scope" option. It states, "By default, a static route is applied to all the interfaces of the Tier-0 gateway... You can optionally apply the static route to a specific set of interfaces of the Tier-0 gateway." This confirms that the scenario described in option A is a possible configuration that limits a route's availability to specific interfaces.

2. VMware NSX Reference Design Guide (Page 68): In the section "Tier-0 Gateway in Active-Active High Availability Mode," the guide discusses routing considerations. For proper function and high availability, it recommends ECMP across all uplinks. A single static default route scoped to only one uplink violates this principle and leads to asymmetric or failed routing paths, which can impact control plane protocols like BGP that rely on a consistent routing table.

3. VMware NSX-T Data Center Troubleshooting Guide (NSX 3.2, Page 218): The BGP troubleshooting section explains neighbor states. The Idle state is the initial state where BGP refuses incoming connections. The error "No route to peer" indicates the local BGP process performed a route lookup for the peer's IP address and failed to find a valid path in its routing table, preventing it from initiating a TCP connection.