A reset (RST) means someone actively tore the connection down: the peer app, a middlebox, or the OS (port closed / queue full). The context around the reset names the culprit.
App-level: process OOM-killed mid-request (check dmesg), request-size limit (nginx 413 sends RST when http2 with some configs), or the upstream actively refusing the payload.
LBs reset connections past idle timeouts mid-stream; corporate firewalls RST on policy (SNI filtering, content type). Resets identical across many clients = middlebox.
netstat -s | grep -i reset / listen queue overflow counters; on the server, net.core.somaxconn and backlog sizing matter under bursts.
curl -v --max-time 10 https://host/path 2>&1 | tail -15 # where exactly the reset lands (connect vs mid-body)sudo journalctl --since '-5 min' | grep -iE 'oom|kill|reset|segfault' ; sudo dmesg -T | tail -10sudo tcpdump -i any -nn 'host <peer> and port 443' -c 50 # RST from the peer = peer-side cause; RST from a middlebox hops = policy/firewall# app crash: fix the app/OOM ; nginx limit: client_max_body_size ; LB idle: raise timeout or add keepalives ; overflow: raise somaxconn/backlogResets at a consistent point in the stream (same byte count) mean a size/policy limit; random-point resets mean crashes or timeouts. tcpdump showing the RST coming from an IP that's neither endpoint = firewall/LB in the path — that changes everything about your debug.
Refused = RST immediately on the initial SYN (nothing listening). Reset mid-connection = established TCP torn down by a peer or middlebox. 'Refused' is a startup problem; 'reset' is a lifetime problem.
No — most resets are ordinary: app close without graceful shutdown, idle reaping, or crash. Reserve suspicion for resets that correlate with specific hosts, payload types, or SNI — those point at filtering.
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