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aa4bb512ea
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Document UDP conntrack ACK loss case study and fix
Created comprehensive troubleshooting guide documenting the multi-layer
debugging of Twilio calls dying at exactly 64 seconds.
### Root Cause:
UDP conntrack timeout (30s) < SIP Timer H (32s) = ACK dropped at kernel
Timeline:
- t+30s: conntrack expires UDP NAT mapping
- t+32s: Asterisk final 200 OK retransmit → Twilio ACK
- Kernel drops ACK (no conntrack entry)
- t+64s: Timer H fires → call dies (2× Timer H = 64s)
### The Fix (applied by flextel agent on docker-2):
```bash
sudo sysctl -w net.netfilter.nf_conntrack_udp_timeout=120
echo "net.netfilter.nf_conntrack_udp_timeout = 120" | \
sudo tee /etc/sysctl.d/99-sip-conntrack.conf
```
120s timeout provides 88s headroom beyond Timer H (32s).
### Documentation Added:
- docs/troubleshooting/udp-conntrack-ack-loss.md - Full case study with:
- Investigation timeline (3 layers: SIP timers, sip-guardian, conntrack)
- Timing conflict tables showing conntrack vs SIP protocol interaction
- Packet capture evidence
- Architectural improvements (ACK fast-path)
- Lessons learned from cross-layer debugging
- README.md - Added troubleshooting entry with quick-fix and case study link
### Agent Thread:
- 008-flextel-applied-conntrack-fix-noting-it-didnt-land-from-your-side.md
Notes that the sysctl fix was applied by flextel agent after diagnosis.
Confirms timing analysis was the smoking gun.
### Defense in Depth:
1. Kernel: conntrack timeout increased (production fix)
2. Userspace: ACK fast-path in sip-guardian (architectural fix)
Both layers now protect against this failure mode.
Credit: Multi-agent debugging via agent-thread protocol. flextel agent
applied the production fix and confirmed the diagnosis.
See: docs/agent-threads/ack-loss-from-twilio-trunk/
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2026-06-22 10:04:49 -06:00 |
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