I'm getting similar results on residential Comcast up here in Michigan, US (Comcast's Heartland region).  Checking from a Google Cloud vm in Iowa, US, I was able to reach m.root-servers.net via both v4 and v6, but it looks like it's routing to the Sao Paulo cluster in both cases (looking at https://m.root-servers.org/, I would have assumed it would have routed to SF's cluster)

test-instance-3:~$ ping m.root-servers.net
PING m.root-servers.net(M.ROOT-SERVERS.NET (2001:dc3::35)) 56 data bytes
64 bytes from M.ROOT-SERVERS.NET (2001:dc3::35): icmp_seq=1 ttl=63 time=141 ms
64 bytes from M.ROOT-SERVERS.NET (2001:dc3::35): icmp_seq=2 ttl=63 time=141 ms
64 bytes from M.ROOT-SERVERS.NET (2001:dc3::35): icmp_seq=3 ttl=63 time=141 ms
^C
--- m.root-servers.net ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2002ms
rtt min/avg/max/mdev = 140.752/140.903/141.091/0.140 ms

test-instance-3:~$ dig +short m.root-servers.net
202.12.27.33

test-instance-3:~$ ping 202.12.27.33
PING 202.12.27.33 (202.12.27.33) 56(84) bytes of data.
64 bytes from 202.12.27.33: icmp_seq=1 ttl=254 time=143 ms
64 bytes from 202.12.27.33: icmp_seq=2 ttl=254 time=140 ms
64 bytes from 202.12.27.33: icmp_seq=3 ttl=254 time=141 ms
^C
--- 202.12.27.33 ping statistics ---
3 packets transmitted, 3 received, 0% packet loss, time 2003ms
rtt min/avg/max/mdev = 140.387/141.368/143.146/1.259 ms

test-instance-3:~$ traceroute -I m.root-servers.net
traceroute to m.root-servers.net (202.12.27.33), 64 hops max
  1   *  *  *
  2   142.251.64.24  140.646ms  140.640ms  140.749ms
  3   187.16.215.148  140.371ms  140.292ms  140.314ms
  4   202.12.27.33  139.841ms  140.324ms  139.980ms

 test-instance-3:~$ dig -x 187.16.215.148
...
148.215.16.187.in-addr.arpa. 6423 IN    PTR     as7500.saopaulo.sp.ix.br.
...  

test-instance-3:~$ traceroute6 m.root-servers.net
traceroute to m.root-servers.net (2001:dc3::35) from 2600:1900:4000:d977:0:1::, 30 hops max, 24 byte packets
 1  * * *
 2  2001:4860:0:1::7cd8 (2001:4860:0:1::7cd8)  140.1891 ms  140.0114 ms  140.0064 ms
 3  as7500.saopaulo.sp.ix.br (2001:12f8::215:148)  140.7670 ms  140.7445 ms  140.7408 ms
 4  M.ROOT-SERVERS.NET (2001:dc3::35)  140.5523 ms  140.4191 ms  140.4163 ms

On Sun, Aug 25, 2024 at 8:18 PM Crist Clark <cjc+nanog@pumpky.net> wrote:
Debated whether to bring this up on the OARC DNS Ops list or NANOG. Seem more of a network-y thing.

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