​​Comcast recently lit up IPv6 native dual stack in the Boston area.

The http://test-ipv6.com/ web site complains about DNS problems unless dnssec is disabled; if it is, I get various timeouts.

Test with IPv4 DNS record 
ok (4.196s)
Test with IPv6 DNS record 
ok (0.115s) using ipv6
Test with Dual Stack DNS record 
timeout (11.882s)
Test for Dual Stack DNS and large packet 
timeout (11.817s)
Test IPv4 without DNS 
ok (0.214s) using ipv4
Test IPv6 without DNS 
ok (0.204s) using ipv6
Test IPv6 large packet 
ok (0.120s) using ipv6
Test if your ISP's DNS server uses IPv6  
slow (8.752s)
Find IPv4 Service Provider 
timeout (11.968s)
Find IPv6 Service Provider 
ok (0.126s) using ipv6 ASN 7922
Test for buggy DNS 
undefined (5.003s)

DNS server addresses look reasonable for Comcast.
DNS 1: 75.75.75.75
DNS 2: 75.75.76.76
DNS 1: 2001:558:feed::1
DNS 2: 2001:558:feed::2

Today, the problem seems consistent with turning dnssec on and off on the router.  If enabled, I have problems; if disabled, I get a clean bill of health out of test-ipv6.com.
                                             - Jim