Friday, March 27, 2009

DNSSEC vs Firewall

A very common cause for DNSSEC validation failure under BIND 9 is firewall issues. Specifically, a firewall that blocks fragments. To work around this, limiting the packet size one is willing to accept so to avoid fragmentation is a good, but temporary, solution.
options {
  edns-udp-size 1460;
This has the side-effect of causing TCP retries on large packets, which are often the DNSKEY responses. However, it also causes DNSSEC to work, so overall it's a good thing.

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