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-216991	CISC-RT-000470	SV-216991r856208_rule		Low

Description
As described in RFC 3682, GTSM is designed to protect a router's IP-based control plane from 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.

Description

As described in RFC 3682, GTSM is designed to protect a router's IP-based control plane from 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 Router RTR Security Technical Implementation Guide	2023-02-17

Details

Check Text ( C-18221r287301_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.

Check Text ( C-18221r287301_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-18219r287302_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