Can't ping the plusnet DNS server

[#1]

Found this rather surprising fact when testing my broadband responses this morning:

Pinging 212.159.6.9 with 32 bytes of data:
Request timed out.
Request timed out.
Request timed out.
Request timed out.

Ping statistics for 212.159.6.9:
    Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),

It's the same for 212.159.6.10.

Is this normal? I'm sure I've successfully pinged the DNS server before. Web pages are redirecting, albeit quite slowly sometimes so I presume the DNS server is up.

Grateful for any explanation.

[#2 · Accepted solution]

The DNS servers have been changed recently. As part of the reconfiguration, they no longer respond to pings.

[#3]

@simonc2 I could be  wrong, but I don't think the  DNS servers respond to ping, by default.

[#4]

Thanks, that explains it.