[PR #5987] [client] Fix mgmt cache bypass overlay #27251

New Issue

saavagebueno · 2026-08-05T07:08:26-04:00

saavagebueno commented

2026-08-05 07:08:26 -04:00

Original Pull Request: https://github.com/netbirdio/netbird/pull/5987

State: closed
Merged: No

Describe your changes

Exit-Node Peer Routing Issue and Fix

Problem

When an exit-node peer installs a 0.0.0.0/0 default route on wt0 before its WireGuard peer entry is active, any socket dialing an off-link address via that route returns kernel ENOKEY.

This deadlocks a specific path: when a remote peer is homed on a different relay instance than the local daemon, the daemon must dial a foreign relay FQDN (e.g. streamline-de-fra1-0.relay.netbird.io). That FQDN is not in the mgmt cache, so it falls through to the normal upstream handler — which takes the overlay-routed dial and fails. No DNS → no relay → no peer handshake → no DNS.

Deterministic, but only triggers when the relay load-balancer puts peers on different instances. Caused the intermittent exit-node e2e failures on rocky9 / debian-12.

Fix

mgmt.Resolver bypass mechanism: mgmt.Resolver gets a dedicated *net.Resolver whose Dial uses nbnet.NewDialer(). On Linux the socket gets SO_MARK=ControlPlaneMark, on darwin IP_BOUND_IF, on Windows IP_UNICAST_IF — the same bypass mechanism gRPC/STUN/TURN/relay-websocket already use. Policy routes keep it on the underlay interface.
Original nameservers: Dialer targets the original pre-NetBird system nameservers, captured from the registerFallback flow. No hardcoded fallback IPs; if the host had no original resolver, the bypass resolver stays nil and the stale-while-revalidate cache serves.
Pool-root domains: Pool-root domains (ServerDomains.Relay[], e.g. relay.netbird.io) are registered through a thin subdomainMatchHandler wrapper, so instance subdomains (streamline-*.relay.netbird.io) route to the mgmt cache.
Cache miss resolution: On cache miss under a pool root, ServeDNS resolves on demand via the bypass resolver, caches the result, and returns it.
OS DNS manager integration: Pool-roots are also pushed into extraDomains so applyHostConfig advertises them as match domains to systemd-resolved / NetworkManager / scutil. Without this, those OS DNS managers would answer the query from the host's global upstream, skipping the handler chain entirely — which is exactly what happened on ubuntu-20.04.

Issue ticket number and link

Stack

Checklist

Is it a bug fix
Is a typo/documentation fix
Is a feature enhancement
It is a refactor
Created tests that fail without the change (if possible)

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Documentation

Select exactly one:

I added/updated documentation for this change
Documentation is not needed for this change (explain why)

Docs PR URL (required if "docs added" is checked)

Paste the PR link from https://github.com/netbirdio/docs here:

https://github.com/netbirdio/docs/pull/__

Summary by CodeRabbit

New Features
- On-demand resolution for instance subdomains under relay domains with deduplicated lookups and cached A/AAAA answers for faster responses.
- Configurable bypass resolver to route DNS queries directly to specified upstream nameservers with robust dialing and failover behavior.
Bug Fixes
- Improved handling and tracking of relay “pool-root” domains during config updates to avoid stale registrations.
- More reliable nameserver fallback, tracking, and failover when upstreams change or are absent.

**Original Pull Request:** https://github.com/netbirdio/netbird/pull/5987 **State:** closed **Merged:** No --- ## Describe your changes # Exit-Node Peer Routing Issue and Fix ## Problem When an exit-node peer installs a 0.0.0.0/0 default route on wt0 before its WireGuard peer entry is active, any socket dialing an off-link address via that route returns kernel ENOKEY. This deadlocks a specific path: when a remote peer is homed on a different relay instance than the local daemon, the daemon must dial a foreign relay FQDN (e.g. streamline-de-fra1-0.relay.netbird.io). That FQDN is not in the mgmt cache, so it falls through to the normal upstream handler — which takes the overlay-routed dial and fails. No DNS → no relay → no peer handshake → no DNS. Deterministic, but only triggers when the relay load-balancer puts peers on different instances. Caused the intermittent exit-node e2e failures on rocky9 / debian-12. ## Fix - **mgmt.Resolver bypass mechanism**: mgmt.Resolver gets a dedicated *net.Resolver whose Dial uses nbnet.NewDialer(). On Linux the socket gets SO_MARK=ControlPlaneMark, on darwin IP_BOUND_IF, on Windows IP_UNICAST_IF — the same bypass mechanism gRPC/STUN/TURN/relay-websocket already use. Policy routes keep it on the underlay interface. - **Original nameservers**: Dialer targets the original pre-NetBird system nameservers, captured from the registerFallback flow. No hardcoded fallback IPs; if the host had no original resolver, the bypass resolver stays nil and the stale-while-revalidate cache serves. - **Pool-root domains**: Pool-root domains (ServerDomains.Relay[], e.g. relay.netbird.io) are registered through a thin subdomainMatchHandler wrapper, so instance subdomains (streamline-*.relay.netbird.io) route to the mgmt cache. - **Cache miss resolution**: On cache miss under a pool root, ServeDNS resolves on demand via the bypass resolver, caches the result, and returns it. - **OS DNS manager integration**: Pool-roots are also pushed into extraDomains so applyHostConfig advertises them as match domains to systemd-resolved / NetworkManager / scutil. Without this, those OS DNS managers would answer the query from the host's global upstream, skipping the handler chain entirely — which is exactly what happened on ubuntu-20.04. ## Issue ticket number and link ## Stack  ### Checklist - [x] Is it a bug fix - [ ] Is a typo/documentation fix - [ ] Is a feature enhancement - [ ] It is a refactor - [ ] Created tests that fail without the change (if possible) > By submitting this pull request, you confirm that you have read and agree to the terms of the [Contributor License Agreement](https://github.com/netbirdio/netbird/blob/main/CONTRIBUTOR_LICENSE_AGREEMENT.md). ## Documentation Select exactly one: - [ ] I added/updated documentation for this change - [x] Documentation is **not needed** for this change (explain why) ### Docs PR URL (required if "docs added" is checked) Paste the PR link from https://github.com/netbirdio/docs here: https://github.com/netbirdio/docs/pull/__  ## Summary by CodeRabbit * **New Features** * On-demand resolution for instance subdomains under relay domains with deduplicated lookups and cached A/AAAA answers for faster responses. * Configurable bypass resolver to route DNS queries directly to specified upstream nameservers with robust dialing and failover behavior. * **Bug Fixes** * Improved handling and tracking of relay “pool-root” domains during config updates to avoid stale registrations. * More reliable nameserver fallback, tracking, and failover when upstreams change or are absent.

saavagebueno added the pull-request label 2026-08-05 07:08:26 -04:00

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Reference: DYNR/netbird#27251