Squid configuration directive dns_v4_fallback

Available in: 3.1  

History:

Changes in 3.1 dns_v4_fallback

New option to prevent Squid from always looking up IPv4 regardless of whether IPv6 addresses are found. Squid will follow a policy of prefering IPv6 links, keeping the IPv4 only as a safety net behind IPv6. 

        Standard practice with DNS is to lookup either A or AAAA records
        and use the results if it succeeds. Only looking up the other if
        the first attempt fails or otherwise produces no results.

        That policy however will cause Squid to produce error pages for some
        servers that advertise AAAA but are unreachable over IPv6.

        If this is ON  Squid will always lookup both AAAA and A, using both.
        If this is OFF Squid will lookup AAAA and only try A if none found.

        WARNING: There are some possibly unwanted side-effects with this on:
                *) Doubles the load placed by Squid on the DNS network.
                *) May negatively impact connection delay times.

Configuration Details:

Option Name:dns_v4_fallback
Replaces:
Requires:--enable-internal-dns
Default Value:dns_v4_fallback on
Suggested Config: 


	Standard practice with DNS is to lookup either A or AAAA records
	and use the results if it succeeds. Only looking up the other if
	the first attempt fails or otherwise produces no results.

	That policy however will cause squid to produce error pages for some
	servers that advertise AAAA but are unreachable over IPv6.

	If this is ON  squid will always lookup both AAAA and A, using both.
	If this is OFF squid will lookup AAAA and only try A if none found.

	WARNING: There are some possibly unwanted side-effects with this on:
		*) Doubles the load placed by squid on the DNS network.
		*) May negatively impact connection delay times.
 

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