🐛After fallback to http2 cloudflared never attempts quic again #1534
Description
Describe the bug
- Our networking was down for a bit
- An instance of cloudflared started, and was unable to connect to quic (as networking was down)
- cloudflared started trying http2 instead (which failed, as we only allow cloudflared to talk quic in our firewall)
- Networking came up
- QUIC was never tried again; and hence cloudflared sat there retrying http2 forever.
To Reproduce
Steps to reproduce the behavior:
- See above: Make quic and http2 fail (e.g. by turning off network; or blocking at firewall)
- Wait 5 minutes for log message "Switching to fallback protocol http2"
- Allow/unblock just quic (not http2)
- Observe that quic is never attempted again without a restart
Expected behavior
Keep attempting quic forever
Environment and versions
- OS: Linux
- Architecture: x86_64
- Version: 2025.9.0
Logs and errors
2025-09-23T19:49:03Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.227
2025-09-23T19:49:03Z INF Retrying connection in up to 2s connIndex=0 event=0 ip=198.41.192.227
2025-09-23T19:49:03Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.192.47
2025-09-23T19:49:13Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.47
2025-09-23T19:49:13Z INF Retrying connection in up to 4s connIndex=0 event=0 ip=198.41.192.47
2025-09-23T19:49:14Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:24Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:24Z INF Retrying connection in up to 8s connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:28Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:49:38Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:49:38Z INF Retrying connection in up to 16s connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:49:39Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:49Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:49Z INF Retrying connection in up to 32s connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:49:54Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:50:04Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:50:04Z INF Retrying connection in up to 1m4s connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:50:05Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.192.37
2025-09-23T19:50:15Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.37
2025-09-23T19:50:15Z INF Retrying connection in up to 1m4s connIndex=0 event=0 ip=198.41.192.37
2025-09-23T19:50:41Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.200.233
2025-09-23T19:50:51Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.200.233
2025-09-23T19:50:51Z INF Retrying connection in up to 1m4s connIndex=0 event=0 ip=198.41.200.233
2025-09-23T19:51:07Z INF Tunnel connection curve preferences: [X25519MLKEM768 CurveP256] connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:51:17Z ERR Failed to dial a quic connection error="failed to dial to edge with quic: timeout: handshake did not complete in time" connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:51:17Z INF Retrying connection in up to 1m4s connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:51:31Z INF Switching to fallback protocol http2 connIndex=0 event=0 ip=198.41.192.107
2025-09-23T19:51:46Z ERR Unable to establish connection with Cloudflare edge error="DialContext error: dial tcp 198.41.200.43:7844: i/o timeout" connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:51:46Z ERR Serve tunnel error error="DialContext error: dial tcp 198.41.200.43:7844: i/o timeout" connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:51:46Z INF Retrying connection in up to 1s connIndex=0 event=0 ip=198.41.200.43
2025-09-23T19:52:02Z ERR Unable to establish connection with Cloudflare edge error="DialContext error: dial tcp 198.41.200.63:7844: i/o timeout" connIndex=0 event=0 ip=198.41.200.63
2025-09-23T19:52:02Z ERR Serve tunnel error error="DialContext error: dial tcp 198.41.200.63:7844: i/o timeout" connIndex=0 event=0 ip=198.41.200.63
2025-09-23T19:52:02Z INF Retrying connection in up to 4s connIndex=0 event=0 ip=198.41.200.63