The scenario involves designing a VMware Cloud Foundation (VCF) stretched cluster with L2 non-uniform connectivity, leveraging NSX (a core component of VCF) for networking. The customer’s past incident, where an attacker injected false routes into their dynamic global routing table, indicates a security vulnerability in the routing protocol. The Tier-0 gateway in NSX handles external connectivity and routing, typically using dynamic routing protocols like BGP (Border Gateway Protocol) or OSPF (Open Shortest Path First) to exchange routes with external routers. The design decision must prevent unauthorized route injection, ensuring the integrity of the routing table.

Context Analysis:

Stretched Cluster with L2 Non-Uniform Connectivity:In VCF 5.2, a stretched cluster spans multiple availability zones (AZs) with L2 connectivity for workload VMs, but the Tier-0 gateway uplinks may use L3 routing to external networks. “Non-uniform” suggests varying latency or bandwidth between sites, but this does not directly impact the routing security concern.

False Routes Injection:This implies the attacker exploited a lack of authentication or filtering in the routing protocol, allowing unauthorized route advertisements to be accepted into the Tier-0 gateway’s routing table.

Tier-0 Gateway:In NSX, the Tier-0 gateway is the edge component that peers with external routers (e.g., top-of-rack switches or upstream routers) and supports dynamic routing protocols like BGP and OSPF.

Routing Security in NSX:

NSX Tier-0 gateways commonly use BGP for external connectivity due to its scalability and flexibility in multi-site deployments like stretched clusters. OSPF is also supported but is less common for external peering in VCF designs.

Route injection attacks occur when an unauthorized device advertises routes without validation, often due to missing authentication mechanisms.

Option Analysis:

A. OSPF MD5 authentication:OSPF supports MD5 authentication to secure routing updates between neighbors. Each OSPF message is hashed with a shared secret key, ensuring only trusted peers can exchange routes. This would prevent false route injection if OSPF were the protocol in use. However, in VCF stretched cluster designs, BGP is the default and recommended protocol for Tier-0 gateway uplinks to external networks, as per the VMware Cloud Foundation Design Guide. OSPF is typically used for internal NSX routing (e.g., between Tier-0 and Tier-1 gateways) rather than external peering. Without evidence that OSPF is used here, and given BGP’s prevalence in such scenarios, this option is less applicable.

B. Gateway Firewall with ECMP:The Gateway Firewall on the Tier-0 gateway filters traffic, not routes. Equal-Cost Multi-Path (ECMP) enhances bandwidth by load-balancing across multiple uplinks but does not inherently secure the routing table. While a firewall could block traffic from malicious sources, it cannot prevent the Tier-0 gateway from accepting false route advertisements in the control plane (routing protocol). Route injection occurs at the routing protocol level, not the data plane, so this option does not address theroot issue. The NSX Administration Guide confirms that firewall rules apply to packet forwarding, not route validation, making this incorrect.

C. Implicit deny for any traffic:An implicit deny rule in the Gateway Firewall blocks all traffic not explicitly allowed, enhancing security for data plane traffic. However, this does not protect the control plane—specifically, the dynamic routing protocol—from accepting false routes. Route injection happens before traffic filtering, as the routing table determines where packets are sent. The VMware Cloud Foundation 5.2 documentation emphasizes that routing security requires protocol-specific measures, not just firewall rules. This option fails to prevent the described attack and is incorrect.

D. BGP peer password:BGP supports authentication via a peer password (MD5-based in NSX), where each BGP session between the Tier-0 gateway and its external peers (e.g., physical routers) uses a shared secret. This ensures that only authenticated peers can advertise routes, preventing unauthorized devices from injecting false routes into the dynamic routing table. In VCF 5.2 stretched cluster deployments, BGP is the standard protocol for Tier-0 uplinks, as it supports multi-site connectivity and ECMP for redundancy. The NSX-T Data Center Design Guide and VCF documentation recommend BGP authentication to secure routing in such environments, directly addressing the customer’s past incident. This is the most relevant and effective design decision.

Conclusion:The architect should chooseBGP peer password (D)as the design decision for the Tier-0 gateway. This secures the BGP routing protocol—widely used in VCF stretched clusters—against false route injection by requiring authentication, aligning with the scenario’s security requirements and NSX best practices.

References:

VMware Cloud Foundation 5.2 Design Guide (Section: NSX Design for Stretched Clusters)

VMware NSX-T Data Center 3.2 Administration Guide (Section: Tier-0 Gateway Routing)

VMware Cloud Foundation 5.2 Planning and Preparation Workbook (Section: Networking Security)

VMware Validated Design for Stretched Clusters (Section: Routing Security)