# Cis GCP Cos 3.2.9

> Ensure IPv6 router advertisements are not accepted

- Skill: `cyberstrikeus/cis-gcp-cos-3-2-9` (Agent Skill)
- Install (CLI): `npx skillmds@latest add cyberstrikeus/cis-gcp-cos-3-2-9`
- Raw SKILL.md: https://api.skillmd.com/api/skills/cyberstrikeus/cis-gcp-cos-3-2-9/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: DevOps & Infra
- Author: cyberstrikeus (https://skillmd.com/u/cyberstrikeus)
- Updated: 2026-09-17
- Page: https://skillmd.com/skills/cyberstrikeus/cis-gcp-cos-3-2-9

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# 3.2.9 Ensure IPv6 router advertisements are not accepted (Automated)

## Description

This setting disables the system's ability to accept IPv6 router advertisements.

## Rationale

It is recommended that systems do not accept router advertisements as they could be tricked into routing traffic to compromised machines. Setting hard routes within the system (usually a single default route to a trusted router) protects the system from bad routes.

## Audit Procedure

Run the following commands and verify output matches:

```bash
# sysctl net.ipv6.conf.all.accept_ra
net.ipv6.conf.all.accept_ra = 0
# sysctl net.ipv6.conf.default.accept_ra
net.ipv6.conf.default.accept_ra = 0
```

## Expected Result

Both sysctl commands should return a value of `0`, confirming that IPv6 router advertisements are not accepted.

## Remediation

Run the following commands to set the active kernel parameters:

```bash
# sysctl -w net.ipv6.conf.all.accept_ra=0
# sysctl -w net.ipv6.conf.default.accept_ra=0
# sysctl -w net.ipv6.route.flush=1
```

`/etc` is stateless on Container-Optimized OS. Therefore, `/etc` cannot be used to make these changes persistent across reboots. The steps mentioned above needs to be performed after every boot.

## CIS Controls

| Controls Version | Control                                                                                                                                                                                                                         | IG 1 | IG 2 | IG 3 |
| ---------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | ---- | ---- | ---- |
| v8               | **12.2 Establish and Maintain a Secure Network Architecture** - Establish and maintain a secure network architecture. A secure network architecture must address segmentation, least privilege, and availability, at a minimum. |      | X    | X    |

## Profile

- Level 2 - Server