28e553bc5f
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Root cause found via pcap analysis: MikroTik with connection-count=N sends UDP from N different source ports (2257, 2258, 2259, ...) all to our single server port 2001. A connect()'d UDP socket only accepts packets from the one connected address, silently dropping ~75% of traffic with conn_count=4. Fix: when tcp_conn_count > 0, leave the UDP socket unconnected and use send_to()/recv_from() instead of send()/recv(). This accepts packets from all MikroTik source ports. This bug also exists in the original C btest-opensource. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
76 lines
2.3 KiB
Bash
Executable File
76 lines
2.3 KiB
Bash
Executable File
#!/usr/bin/env bash
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# Capture btest traffic for debugging multi-connection issues.
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#
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# Usage:
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# # Terminal 1: Start capture
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# sudo ./scripts/debug-capture.sh capture <interface> [mikrotik_ip]
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#
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# # Terminal 2: Run server or client
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# ./target/release/btest -s -a admin -p password -vv
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#
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# # Terminal 1: Stop with Ctrl+C, then analyze
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# ./scripts/debug-capture.sh analyze
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set -euo pipefail
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cd "$(dirname "$0")/.."
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CMD="${1:?Usage: $0 <capture|analyze> [interface] [mikrotik_ip]}"
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PCAP_FILE="dist/btest-debug.pcap"
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mkdir -p dist
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case "$CMD" in
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capture)
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IFACE="${2:?Specify interface (e.g., en0, eth0)}"
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MK_IP="${3:-}"
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FILTER="port 2000 or portrange 2001-2100 or portrange 2257-2356"
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if [[ -n "$MK_IP" ]]; then
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FILTER="host $MK_IP and ($FILTER)"
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fi
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echo "Capturing btest traffic on $IFACE..."
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echo "Filter: $FILTER"
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echo "Output: $PCAP_FILE"
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echo "Press Ctrl+C to stop"
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echo ""
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tcpdump -i "$IFACE" -w "$PCAP_FILE" -s 128 "$FILTER"
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;;
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analyze)
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if [[ ! -f "$PCAP_FILE" ]]; then
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echo "No capture file found at $PCAP_FILE"
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echo "Run: sudo $0 capture <interface> first"
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exit 1
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fi
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echo "=== TCP Control Channel (port 2000) ==="
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echo ""
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echo "--- Connection summary ---"
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tcpdump -r "$PCAP_FILE" -n 'tcp port 2000 and (tcp[tcpflags] & tcp-syn != 0)' 2>/dev/null | head -20
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echo ""
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echo "--- All TCP control data (first 64 bytes of payload) ---"
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tcpdump -r "$PCAP_FILE" -n -X 'tcp port 2000 and tcp[tcpflags] & tcp-push != 0' 2>/dev/null | head -100
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echo ""
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echo "=== UDP Data Ports ==="
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echo ""
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echo "--- UDP port usage ---"
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tcpdump -r "$PCAP_FILE" -n 'udp' 2>/dev/null | awk '{print $3, $5}' | sort | uniq -c | sort -rn | head -20
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echo ""
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echo "--- Timing of first packets per connection ---"
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tcpdump -r "$PCAP_FILE" -n -tt 'tcp port 2000 and (tcp[tcpflags] & tcp-syn != 0)' 2>/dev/null | head -20
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echo ""
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echo "Full capture at: $PCAP_FILE"
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echo "Open in Wireshark: wireshark $PCAP_FILE"
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;;
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*)
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echo "Usage: $0 <capture|analyze> [interface] [mikrotik_ip]"
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exit 1
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;;
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esac
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