High TCP retransmissions / packet loss Networking Origin: Network OSI layer 4 · Transport Last updated 5 Nov 2026

Networking: netstat -s: segments retransmitted / Wireshark: TCP Retransmission, TCP Dup ACK — packet loss on the path

Packets are being lost, so TCP resends them and throughput collapses.

Exact message you may see segments retransmittedTCP RetransmissionTCP Spurious Retransmissionhigh packet loss retransmits
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Seen on: Linux Networking

Meaning

Rising retransmitted counters or Wireshark's "TCP Retransmission" flags mean loss or heavy congestion. Locate the loss with mtr, check duplex/CRC counters, Wi-Fi quality, overloaded links, bad cables and queue drops on routers.

Common causes

  • Congested or overloaded link
  • Faulty cable, SFP or duplex mismatch
  • Poor Wi-Fi signal or interference
  • Bufferbloat or router queue drops
  • Firewall/IPS dropping packets

⚡ Quick fix

  1. Run mtr -rwzc 100 host to find the lossy hop
  2. Check interface errors and fix cabling/duplex
  3. Reduce load or shape/queue traffic

Detailed fix by platform

Linux

  1. bash
    nstat -az TcpRetransSegs TcpOutSegs
mtr -rwzc 100 example.com

How to diagnose

  1. Loss — At which hop?
  2. Interface errors — Present?
  3. Link — Saturated?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Network. Errors that are often confused with or caused by this one (click to open):

Cannot assign requested address (EADDRNOTAVAIL) — Networking: connect: Cannot assign requested address — ephemeral port range exhausted by TIME_WAIT connections (Networking)Cannot assign request…Connections hang on large transfers (PMTU black hole) — Networking: SSH/HTTPS connects but hangs on large data — path MTU discovery black hole (Networking)Connections hang on l…Duplex mismatch: late collisions / CRC errors — Networking: Duplex mismatch — late collisions, runts and CRC errors on the switch port (Networking)Duplex mismatch: late…Many sockets in CLOSE_WAIT — Networking: Thousands of sockets in CLOSE_WAIT — the application is not closing its side of the connection (Networking)Many sockets in CLOSE…nfs: server not responding, still trying — Networking: kernel: nfs: server nas01 not responding, still trying / nfs: server nas01 OK (Networking)nfs: server not respo…TCP ZeroWindow / TCP Window Full — Networking: Wireshark: TCP ZeroWindow, TCP Window Full — the receiver can't keep up and tells the sender to stop (Networking)TCP ZeroWindow / TCP …times the listen queue of a socket overflowed — Networking: netstat -s: 1523 times the listen queue of a socket overflowed — accept queue full, connections dropped (Networking)times the listen queu…UDP RcvbufErrors / packet receive errors — Networking: netstat -su: packet receive errors, receive buffer errors — UDP datagrams dropped by a full socket buffer (Networking)UDP RcvbufErrors / pa…High TCP …

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