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Allow configuration of TCP keepalive for NIO TCP connections #420
Description
When dnsjava receives a truncated UDP response, it retries the query over TCP using NioTcpClient. That created TCP connection may remain open for reuse, but currently there is no way to configure TCP keepalive. A firewall or other network device may silently drop an idle connection, causing later queries that reuse it to fail.
Enabling SO_KEEPALIVE on NIO TCP connections and allowing callers to configure the keepalive timing and probe count would prevent that. Suggested system property names and defaults:
| Property | Default | Socket option |
|---|---|---|
| dnsjava.tcp.keepalive | true | SO_KEEPALIVE |
| dnsjava.tcp.keepidle | 900 seconds | TCP_KEEPIDLE |
| dnsjava.tcp.keepinterval | 75 seconds | TCP_KEEPINTERVAL |
| dnsjava.tcp.keepcount | 9 probes | TCP_KEEPCOUNT |
Activity
ibauersachs commentedon Oct 20, 2026
Thanks for the suggestion. While these settings might help, they go into territory of RFC7828 and should probably be implemented together. Would you mind contributing this with a PR?