Skip to content

docs(networking): document host firewall and node IPv6 behavior #574

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Open
Aleksei Sviridkin (lexfrei) wants to merge 1 commit into
base: main
Choose a base branch
from
Open

docs(networking): document host firewall and node IPv6 behavior #574

Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
13 changes: 13 additions & 0 deletions content/en/docs/next/networking/architecture.md
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -394,6 +394,19 @@ spec:
- cluster
```

### Host Firewall and Node IPv6

Cozystack enables Cilium's host firewall (`hostFirewall.enabled: true`) to enforce the system-port restrictions described above on the nodes themselves. The Cilium IPv6 datapath stays disabled (`ipv6.enabled: false`), since pod networking is provided by Kube-OVN.

In upstream Cilium this combination drops all IPv6 traffic on the node's network devices before any policy evaluation. This breaks IPv6 Neighbor Discovery and, with it, all node-level IPv6 connectivity — for example, BGP unnumbered peering over link-local addresses on L3 fabrics. A `CiliumClusterwideNetworkPolicy` cannot allow this traffic back, because the drop happens before policy enforcement.

The Cilium image shipped with Cozystack carries a BPF patch that passes IPv6 to the kernel stack instead, matching the behavior with the host firewall disabled. The patch is carried until an equivalent fix is available upstream. Practical consequences:

@gemini-code-assist gemini-code-assist Bot Jun 10, 2026

Copy link
Copy Markdown
Contributor

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

medium

Improve the phrasing from 'matching the behavior with the host firewall disabled' to 'matching the behavior when the host firewall is disabled' for better clarity and grammatical correctness.

Suggested change
The Cilium image shipped with Cozystack carries a BPF patch that passes IPv6 to the kernel stack instead, matching the behavior with the host firewall disabled. The patch is carried until an equivalent fix is available upstream. Practical consequences:
The Cilium image shipped with Cozystack carries a BPF patch that passes IPv6 to the kernel stack instead, matching the behavior when the host firewall is disabled. The patch is carried until an equivalent fix is available upstream. Practical consequences:


- Node IPv6 (Neighbor Discovery, BGP over link-local addresses, and any other node-level IPv6 traffic) keeps working with the host firewall enabled.
- Cilium host policies apply to IPv4 only. Node IPv6 is not filtered by Cilium; if nodes exposed over IPv6 need filtering, it must be done by other means.

To opt out of the host firewall entirely, set `cilium.hostFirewall.enabled: false` in the values of the `cozystack.cilium` Package. Note that this also disables all IPv4 host policies, including the system-port restrictions.

## Observability with Hubble

Hubble provides network traffic visibility for the Cilium data plane. It is
Expand Down