I am posting this example of the IPv6 vs IPv4 reliability on my Comcast connection as a comment because the official review update will not allow imbedded code (which is needed to illustrate my point).
Shown below is a prime example of the problem. This is of course, not Comcast's fault; it is just an indication of the current state of IPv6 implementation on the Internet (and it does not just occur with Yahoo!):
C:\>ping l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [2001:4998:f00d:1fc::c:1103]
from 2601:5:c80:a1:e291:f5ff:fe95:beac with 32 bytes of data:
Reply from 2001:4998:f00d:1fc::c:1103: time=24ms
Reply from 2001:4998:f00d:1fc::c:1103: time=23ms
Reply from 2001:4998:f00d:1fc::c:1103: time=40ms
Reply from 2001:4998:f00d:1fc::c:1103: time=24ms
Ping statistics for 2001:4998:f00d:1fc::c:1103:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 23ms, Maximum = 40ms, Average = 27ms
C:\>ping l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [2001:4998:f00b:1fb::c:1101]
from 2601:5:c80:a1:e291:f5ff:fe95:beac with 32 bytes of data:
Reply from 2001:4998:f00b:1fb::c:1101: time=49ms
Reply from 2001:4998:f00b:1fb::c:1101: time=46ms
Reply from 2001:4998:f00b:1fb::c:1101: time=44ms
Reply from 2001:4998:f00b:1fb::c:1101: time=50ms
Ping statistics for 2001:4998:f00b:1fb::c:1101:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 44ms, Maximum = 50ms, Average = 47ms
C:\>ping l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [2001:4998:f00b:1fb::c:1103]
from 2601:5:c80:a1:e291:f5ff:fe95:beac with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.
Ping statistics for 2001:4998:f00b:1fb::c:1103:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
An attempt to access
http://my.yahoo.com during the above time frame (with native IPv6 active) results in an extremely long delay (like several minutes) in loading the Yahoo! start page, or a browser timeout. And once again I will reiterate that this symptom also happens on sites other than Yahoo!.
Shown below are repeated successfull IPv4 pings to the same host name:
C:\>ping -4 l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [206.190.56.191] with 32 bytes of data:
Reply from 206.190.56.191: bytes=32 time=34ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Ping statistics for 206.190.56.191:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 33ms, Maximum = 34ms, Average = 33ms
C:\>ping -4 l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [206.190.56.191] with 32 bytes of data:
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Ping statistics for 206.190.56.191:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 32ms, Maximum = 33ms, Average = 32ms
C:\>ping -4 l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [206.190.56.191] with 32 bytes of data:
Reply from 206.190.56.191: bytes=32 time=31ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Ping statistics for 206.190.56.191:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 31ms, Maximum = 32ms, Average = 31ms
C:\>ping -4 l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [206.190.56.191] with 32 bytes of data:
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=35ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Ping statistics for 206.190.56.191:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 33ms, Maximum = 35ms, Average = 33ms
C:\>ping -4 l.yimg.com
Pinging ds-fo-anyycs-l.ay1.b.yahoodns.net [206.190.56.191] with 32 bytes of data:
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Reply from 206.190.56.191: bytes=32 time=33ms TTL=54
Reply from 206.190.56.191: bytes=32 time=32ms TTL=54
Ping statistics for 206.190.56.191:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 32ms, Maximum = 33ms, Average = 32ms
