The Cisco BGP router must be configured to enable the Generalized TTL Security Mechanism (GTSM).
Overview
| Finding ID | Version | Rule ID | IA Controls | Severity |
| V-216999 | CISC-RT-000470 | SV-216999r855842_rule | CCI-002385 | low |
| Description | ||||
| As described in RFC 3682, 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 IOS XE Router RTR Security Technical Implementation Guide | 2025-05-16 | |||
Details
Check Text (C-216999r855842_chk)
Review the BGP configuration to verify that TTL security has been configured for each external neighbor as shown in the example below:
router bgp xx
no synchronization
bgp log-neighbor-changes
neighbor x.1.1.9 remote-as yy
neighbor x.1.1.9 password xxxxxxxx
neighbor x.1.1.9 ttl-security hops 1
neighbor x.2.1.7 remote-as zz
neighbor x.2.1.7 password xxxxxxxx
neighbor x.2.1.7 ttl-security hops 1
If the router is not configured to use GTSM for all Exterior Border Gateway Protocol peering sessions, this is a finding.
Fix Text (F-18227r288160_fix)
Configure TTL security on all external BGP neighbors as shown in the example below:
R1(config)#router bgp xx
R1(config-router)#neighbor x.1.1.9 ttl-security hops 1
R1(config-router)#neighbor x.2.1.7 ttl-security hops 1