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Winsock name resolution APIs use separate cache entries for AF_UNSPEC and AF_INET/AF_INET6 queries

Article ID: 2299432 - View products that this article applies to.

SYMPTOMS

After an application calls getaddrinfo with AF_UNSPEC on hints, if you call getaddrinfo again with AF_INET/AF_INET6, the function doesn't use the DNS cache and sends a DNS query to the wire. DnsQuery with option DNS_QUERY_NO_WIRE_QUERY may fail with DNS_ERROR_RECORD_DOES_NOT_EXIST even after an application calls getaddrinfo.

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CAUSE

When IE or an application calls getaddrinfo with AF_UNSPEC on a machine which has IPv4 and Ipv6 addresses, it results in dual address query from winsock to dns. Dns caches these dual address queries into a bucket with a specific private flag so that it can only be retrieved through application calling that flag (only winsock APIs calling getaddrinfo but not through DnsQuery publicly documented flags).

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RESOLUTION

Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section of this article.

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MORE INFORMATION

Below are two common scenarios for this issue.

Scenario A:

1 Start Network monitor and monitor DNS traffic.

2 Call getaddrinfo for a name using AF_UNSPEC flags on hints (A pointer to an addrinfo structure)
for the addrinfo Structure, please refer to MSDN document:
http://msdn.microsoft.com/en-us/library/ms737530(v=VS.85).aspx

(http://msdn.microsoft.com/en-us/library/ms737530(v=VS.85).aspx)

3 Call getaddrinfo for the same name using AF_INET.

4 Call getaddrinfo for the same name using AF_UNSPEC.

Expected result:

Only the second step should send a query to the wire.

Actual result:

Steps 3 and 4 also send a query to the wire and not use cache.

Scenario B:

1 Call getaddrinfo for a name using AF_UNSPEC on hints.

2 Call DnsQuery with option DNS_QUERY_NO_WIRE_QUERY
(Windows 2000 Server and Windows 2000 Professional: use DNS_QUERY_CACHE_ONLY flag instead.)

Expected result:

DsnQuery can get the record from DNS cache.

Actual result:

DnsQuery fails with DNS_ERROR_RECORD_DOES_NOT_EXIST.

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Note This is a "FAST PUBLISH" article created directly from within the Microsoft support organization. The information contained herein is provided as-is in response to emerging issues. As a result of the speed in making it available, the materials may include typographical errors and may be revised at any time without notice. See Terms of Use

(http://go.microsoft.com/fwlink/?LinkId=151500)

for other considerations.

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