Ubuntu
eglibc package

  1. Bug #417757
  2. Comment #146

Comment 146 for bug 417757

Revision history for this message
Per Heldal (heldal) wrote : Re: [karmic regression] all network apps / browsers suffer from multi-second delays by default due to IPv6 DNS lookups

Slight update to #142.

I may have gotten protocol orders wrong in my analysis, or the dns-lookup-mechanism has been altered in the last libc update. The net result however, is still that every attempt by an application to connect to a v4-only host is preceded by a dns-request that result in a lost nxdomain response. Example: capturing DNS packets while connecting to a webserver with no v6-support reveal the following order of DNS queries and responses:

1. The client searches for an AAAA record. The DNS-server returns SOA with noerror.

2. The client tries the local variant of the AAAA record. The DNS-server returns NXDOMAIN which is lost in the faulty DNS-forwarder.

3. After timeout (20sec) the client goes looking for an A-record and succeeds.

Wouldn't it be preferable to prioritise differently? The client could send concurrent requests for A and AAAA, and drop the attempt on the local variant of AAAA when it gets one or more valid a-records.