ipsec: T9254: do not emit ESN transforms in IKE proposals by rockfish-vyos · Pull Request #5429 · vyos/vyos-1x

rockfish-vyos · 2026-08-27T15:38:33Z

Change summary
I have two VyOS routers in an HA pair with the same configuration. One runs 2026.06.20-0050-rolling and the IPsec tunnel to a Cisco FTD comes up fine. The other ran 2026.08.14 and then 2026.08.27, and the tunnel never establishes on either.

strongSwan is the same version on both (6.0.6-1+vyos0). The difference is in the generated swanctl.conf. The newer images add -noesn variants to the proposals line, so four proposals instead of two, and the IKE_SA_INIT grows from 340 to 436 bytes.

ESN is a CHILD_SA transform (RFC 7296, Transform Type 5). It does not belong in an IKE_SA proposal. The FTD drops the packet without answering: no NO_PROPOSAL_CHOSEN, no INVALID_KE_PAYLOAD, nothing. So the tunnel never comes up and there is nothing in the logs to explain it.

The fix adds an esn parameter to get_esp_ike_cipher(), defaulting to True so ESP output does not change, and passes esn=False at the four places that render IKE proposals: peer.j2, profile.j2, remote_access.j2 and l2tp.j2. The five esp_proposals call sites are untouched.

how-to test
On the FTD I captured the outside interface while the affected node tried to connect. Four IKE_SA_INIT packets of 436 bytes arrived and the FTD never replied. A minute later the working node sent a 340-byte one from the same public address and got an answer in 6 ms.

I edited the proposals line in the generated swanctl.conf by hand to remove the -noesn entries and ran swanctl --load-all. The tunnel came up within seconds. Nothing else was changed. That node had not been able to establish it for weeks.

I could not run the smoketests. They need a live VyOS instance and both my routers are on the June build. I updated the proposals assertions in test_vpn_ipsec.py to match the new output but they have not been executed, so they are worth a careful look. The esp_proposals assertions are unchanged.

get_esp_ike_cipher() renders both IKE_SA proposals and CHILD_SA proposals. It unconditionally appended the -esn / -noesn variants, which are only meaningful for ESP: ESN is Transform Type 5 per RFC 7296 section 3.3.2 and is defined for CHILD_SAs only. Emitting ESN in an IKE_SA proposal breaks interoperability with implementations that reject the malformed payload without replying at all. Observed against a Cisco FTD: the IKE_SA_INIT is silently discarded, no NO_PROPOSAL_CHOSEN and no INVALID_KE_PAYLOAD, so the tunnel never comes up and nothing on the initiator side explains it. Add an explicit esn parameter defaulting to True so ESP behaviour is unchanged, and pass esn=False at the four IKE call sites: peer.j2, profile.j2, remote_access.j2 and l2tp.j2. The five esp_proposals call sites keep ESN. ike_group could have served as the discriminator, since IKE call sites do not pass it, but that coupling is incidental: the argument only exists to resolve PFS. Smoke test assertions on the proposals lines are updated accordingly; the esp_proposals assertions are left untouched.

github-actions · 2026-08-27T15:38:47Z

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mergify · 2026-08-27T15:39:16Z

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coderabbitai · 2026-08-27T15:39:26Z

📝 Walkthrough

Summary by CodeRabbit

Bug Fixes
- Corrected IPsec IKE proposal generation to prevent malformed ESN suffixes.
- Improved compatibility with implementations that reject ESN markers in IKE proposals.
- Preserved ESN handling for ESP proposals while standardizing IKE proposal output across supported VPN configurations.

Walkthrough

The IPsec proposal filter now excludes ESN suffixes from IKE proposals. Swanctl templates pass esn=False for IKE connections. Smoke tests update IKE expectations while preserving ESN-specific ESP expectations.

Changes

IKE ESN proposal handling

Layer / File(s)	Summary
Gate ESN suffix generation `python/vyos/template.py`	`get_esp_ike_cipher` accepts `esn=True` and gates `-esn` and `-noesn` suffix generation on that parameter.
Disable ESN in swanctl IKE templates `data/templates/ipsec/swanctl/l2tp.j2`, `data/templates/ipsec/swanctl/peer.j2`, `data/templates/ipsec/swanctl/profile.j2`, `data/templates/ipsec/swanctl/remote_access.j2`	The templates pass `esn=False` when they render IKE proposals.
Update IPsec proposal expectations `smoketest/scripts/cli/test_vpn_ipsec.py`	Smoke tests remove ESN alternatives from IKE proposal expectations and retain ESN differences for ESP proposals.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 17.65% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 2 files. (4 skipped: …	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Title check	✅ Passed	The title clearly and concisely identifies the main change: preventing ESN transforms from being emitted in IKE proposals.
Description check	✅ Passed	The description directly explains the interoperability issue, the esn=False implementation, affected templates, preserved ESP behavior, and test status.

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Explanation

Docstring coverage is 17.65% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 17 functions across 2 files. (4 skipped: 4 unsupported.)

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Inline comments:
In `@smoketest/scripts/cli/test_vpn_ipsec.py`:
- Line 255: Update all single-proposal assertions in the VPN IPsec smoke tests,
including the cases around the referenced proposal expectations, to compare
complete stripped configuration lines or require the expected value together
with the line terminator. Replace shortened assertIn checks that can match
prefixes, while preserving the intended proposal values.

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📒 Files selected for processing (6)

data/templates/ipsec/swanctl/l2tp.j2
data/templates/ipsec/swanctl/peer.j2
data/templates/ipsec/swanctl/profile.j2
data/templates/ipsec/swanctl/remote_access.j2
python/vyos/template.py
smoketest/scripts/cli/test_vpn_ipsec.py

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Prefer storing Jinja2 templates as discrete files in `data/templates/` rather than inline Python strings