I happened to notice that I cannot query or ping m.root-servers.net's IPv4 address from my home Comcast connection (SF Bay Area). IPv6 works. All of the other root servers are reachable via both IPv4 and IPv6.

Just me or all Comcast users?

Obviously, nothing critical. My DNS servers will work just fine with one root unavailable on one protocol. But curious what's broken. Been this way for at least a couple of weeks.

Compare IPv4 and IPv6 traceroutes,

Mac-Air:~ fred$ traceroute -I m.root-servers.net

traceroute to m.root-servers.net (202.12.27.33), 64 hops max, 72 byte packets

 1  moat (192.168.64.90)  3.004 ms  1.409 ms  1.155 ms

 2  10.60.234.131 (10.60.234.131)  14.354 ms  17.153 ms  14.451 ms

 3  po-313-1222-rur202.pleasanton.ca.sfba.comcast.net (96.110.179.157)  14.296 ms  11.150 ms  11.279 ms

 4  po-200-xar02.pleasanton.ca.sfba.comcast.net (68.85.155.117)  11.752 ms  10.195 ms  11.783 ms

 5  be-248-rar01.pleasanton.ca.sfba.comcast.net (96.108.99.129)  14.261 ms  11.228 ms  13.187 ms

 6  be-398-ar01.hayward.ca.sfba.comcast.net (162.151.87.225)  13.577 ms  13.552 ms  13.725 ms

 7  * * *

 8  * * *

 9  * * *

10  * * *

11  * * *

12  *^C

Mac-Air:~ fred$ traceroute6 -I m.root-servers.net

traceroute6 to m.root-servers.net (2001:dc3::35) from 2601:644:8f01:3b0:c842:51d6:e589:5203, 64 hops max, 16 byte packets

 1  2601:644:8f01:3b0:4262:31ff:fe01:b8  1.753 ms  1.765 ms  1.343 ms

 2  2001:558:101e:54::2  14.526 ms  26.113 ms  32.365 ms

 3  po-313-1221-rur201.pleasanton.ca.sfba.comcast.net  28.170 ms  14.109 ms  11.374 ms

 4  po-200-xar01.pleasanton.ca.sfba.comcast.net  11.746 ms  20.031 ms  42.526 ms

 5  * * *

 6  * * *

 7  * * *

 8  lo-0-v6.ear2.sanjose1.level3.net  15.106 ms  14.454 ms  13.240 ms

 9  pt.telekomu.edge1.losangeles9.level3.net  15.921 ms  17.188 ms  16.294 ms

10  m.root-servers.net  17.032 ms  15.169 ms  14.892 ms