# IP fragment reassembly timeout: packet dropped (fragmentation timeout exceeded)

- **ID:** `networking/ip-fragment-timeout-reassembly-failed`
- **Domain:** networking
- **Category:** network_error
- **Error Code:** `ETIMEDOUT`
- **Verification:** ai_generated
- **Fix Rate:** 75%

## Root Cause

A fragmented IP packet was not fully reassembled within the system's timeout (typically 30-60 seconds), causing all received fragments to be discarded, often due to high packet loss or mismatched PMTU.

## Version Compatibility

| Version | Status | Introduced | Deprecated |
|---------|--------|------------|------------|
| Linux kernel 5.15 | active | — | — |
| Linux kernel 6.1 | active | — | — |
| FreeBSD 13.2 | active | — | — |

## Workarounds

1. **Reduce the MTU on the interface to avoid fragmentation entirely: `ip link set dev eth0 mtu 1400`** (85% success)
   ```
   Reduce the MTU on the interface to avoid fragmentation entirely: `ip link set dev eth0 mtu 1400`
   ```
2. **Enable PMTU discovery and set the DF (Don't Fragment) flag on UDP sockets: `sysctl -w net.ipv4.ip_no_pmtu_disc=0` and ensure firewalls do not block ICMP 'Fragmentation Needed' messages.** (80% success)
   ```
   Enable PMTU discovery and set the DF (Don't Fragment) flag on UDP sockets: `sysctl -w net.ipv4.ip_no_pmtu_disc=0` and ensure firewalls do not block ICMP 'Fragmentation Needed' messages.
   ```
3. **Increase the reassembly queue size to handle bursts: `sysctl -w net.ipv4.ipfrag_max_dist=64` and `sysctl -w net.ipv4.ipfrag_high_thresh=8388608`** (70% success)
   ```
   Increase the reassembly queue size to handle bursts: `sysctl -w net.ipv4.ipfrag_max_dist=64` and `sysctl -w net.ipv4.ipfrag_high_thresh=8388608`
   ```

## Dead Ends

- **** — This only delays the inevitable; if the underlying packet loss is not fixed, fragments will still be dropped after the longer timeout, and it may cause memory exhaustion from pending fragments. (60% fail)
- **** — This breaks legitimate fragmented traffic like large UDP datagrams or certain VPN protocols, leading to connectivity loss for those applications. (80% fail)
- **** — Rebooting resets state temporarily but does not address the root cause of packet loss (e.g., a faulty link or MTU mismatch), so the error returns quickly. (90% fail)