UDP RcvbufErrors / packet receive errors Networking Origin: Network OSI layer 4 · Transport Last updated 5 Nov 2026

Networking: netstat -su: packet receive errors, receive buffer errors — UDP datagrams dropped by a full socket buffer

UDP packets arrive faster than the application reads them, so the kernel throws the extras away.

Exact message you may see packet receive errors UDPreceive buffer errorsUDP packets dropped RcvbufErrorsUdp: InErrors
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Seen on: Linux Networking

Meaning

UDP has no flow control: when the socket buffer is full, RcvbufErrors rises and data is lost (logs, metrics, VoIP, DNS, syslog). Read faster or in more threads, increase net.core.rmem_max and the socket's SO_RCVBUF, and reduce the sender's rate.

Common causes

  • Receiver slower than the sender
  • Small rmem_default/rmem_max
  • Burst traffic (syslog, StatsD, video)
  • Single-threaded reader
  • CPU starvation

⚡ Quick fix

  1. Check counters: nstat -az UdpRcvbufErrors
  2. Raise net.core.rmem_max and set SO_RCVBUF
  3. Add reader threads or slow the sender

Detailed fix by platform

Linux

  1. bash
    nstat -az UdpInErrors UdpRcvbufErrors
sudo sysctl -w net.core.rmem_max=26214400 net.core.rmem_default=26214400

How to diagnose

  1. RcvbufErrors — Rising?
  2. Buffer — Large enough?
  3. Reader — Fast enough?

🔧 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):

arp -a shows (incomplete) — Networking: `arp -n` shows (incomplete) / Destination Host Unreachable — no ARP reply from the next hop (Networking)arp -a shows (incompl…Cannot assign requested address (EADDRNOTAVAIL) — Networking: connect: Cannot assign requested address — ephemeral port range exhausted by TIME_WAIT connections (Networking)Cannot assign request…High TCP retransmissions / packet loss — Networking: netstat -s: segments retransmitted / Wireshark: TCP Retransmission, TCP Dup ACK — packet loss on the path (Networking)High TCP retransmissi…ICMP Destination unreachable (Port unreachable) — Networking: ICMP Destination unreachable (Port unreachable) — UDP packet sent to a port where nothing is listening (Networking)ICMP Destination unre…Port forwarding not working (CGNAT / double NAT) — Networking: Port forwarding configured but the port stays closed — carrier-grade NAT (CGNAT) or double NAT (Networking)Port forwarding not w…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 …WireGuard: Handshake did not complete after 5 seconds — Networking: Handshake for peer did not complete after 5 seconds, retrying (try 2) — WireGuard tunnel never establishes (Networking)WireGuard: Handshake …UDP Rcvbu…

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