Cisco ACI must be configured to enable the Generalized TTL Security Mechanism (GTSM) for BGP sessions.
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-272094 | CACI-RT-000034 | SV-272094r1114284_rule | Low |
| Description |
| GTSM is designed to protect a router's IP-based control plane from denial-of-service (DoS) attacks. Many attacks focused on CPU load and line-card overload can be prevented by implementing GTSM on all Exterior Border Gateway Protocol speaking routers. GTSM is based on the fact that the vast majority of control plane peering is established between adjacent routers, that is, the Exterior Border Gateway Protocol peers are either between connecting interfaces or between loopback interfaces. Since TTL spoofing is considered nearly impossible, a mechanism based on an expected TTL value provides a simple and reasonably robust defense from infrastructure attacks based on forged control plane traffic. |
| STIG | Date |
| Cisco ACI Router Security Technical Implementation Guide | 2025-06-18 |
Details
| Check Text (C-76144r1063677_chk) |
| Review the BGP configuration to verify that TTL security has been configured for each external neighbor as shown in the example below: policy BGP_Peer_Profile no neighbor 10.1.1.1 ebgp-multihop neighbor 10.1.1.1 ttl-security If the Cisco ACI is not configured to use GTSM for all Exterior BGP peering sessions, this is a finding. |
| Fix Text (F-76051r1114283_fix) |
| Configure TTL security on all external BGP neighbors as shown in the example below: 1. Access the BGP Peer Connectivity Profile. policy BGP_Peer_Profile 2. Disable Multihop for external neighbor. no neighbor 10.1.1.1 ebgp-multihop 3. Enable TTL security on the neighbor. neighbor 10.1.1.1 ttl-security |