Cloudflare DNS - `nslookup` fails for IPv6 DNS sometimes, but always works for IPv4 DNS

Zero Trust 1.1.1.1
1

I’m on an FTTH connection that has both IPv4 and IPv6 assigned to it. My ISP is Airtel and my closest Cloudflare datacentre is BLR. I realised that querying for DNS records to any of the 3 Cloudflare DNS services over IPv4 works perfectly fine, but it often fails on IPv6. By often, I mean 95% of the time. On the other hand, it works perfectly fine Google DNS be it IPv4 or IPv6.

By IPv4 and IPv6, I mean the IPv4 / IPv6 DNS server I am connecting to. My network is dual-stack itself throughout the test. Here’s some output from my tests:

Google DNS IPv4

user@host:~$ time nslookup cloudflare.com 8.8.8.8
Server:         8.8.8.8
Address:        8.8.8.8#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.113s
user    0m0.004s
sys     0m0.017s
user@host:~$ time nslookup cloudflare.com 8.8.4.4
Server:         8.8.4.4
Address:        8.8.4.4#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.107s
user    0m0.013s
sys     0m0.009s

Cloudflare DNS IPv4

user@host:~$ time nslookup cloudflare.com 1.1.1.1
Server:         1.1.1.1
Address:        1.1.1.1#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.030s
user    0m0.017s
sys     0m0.004s
user@host:~$ time nslookup cloudflare.com 1.0.0.1
Server:         1.0.0.1
Address:        1.0.0.1#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.029s
user    0m0.013s
sys     0m0.008s
user@host:~$ time nslookup cloudflare.com 1.1.1.2
Server:         1.1.1.2
Address:        1.1.1.2#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.032s
user    0m0.017s
sys     0m0.005s
user@host:~$ time nslookup cloudflare.com 1.0.0.2
Server:         1.0.0.2
Address:        1.0.0.2#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.032s
user    0m0.005s
sys     0m0.017s
user@host:~$ time nslookup cloudflare.com 1.1.1.3
Server:         1.1.1.3
Address:        1.1.1.3#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.033s
user    0m0.007s
sys     0m0.014s
user@host:~$ time nslookup cloudflare.com 1.0.0.3
Server:         1.0.0.3
Address:        1.0.0.3#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.034s
user    0m0.010s
sys     0m0.011s

Google DNS IPv6

user@host:~$ time nslookup cloudflare.com 2001:4860:4860::8888
Server:         2001:4860:4860::8888
Address:        2001:4860:4860::8888#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.094s
user    0m0.014s
sys     0m0.007s
user@host:~$ time nslookup cloudflare.com 2001:4860:4860::8844
Server:         2001:4860:4860::8844
Address:        2001:4860:4860::8844#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.102s
user    0m0.000s
sys     0m0.021s

Cloudflare DNS IPv6

user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1111
;; connection timed out; no servers could be reached



real    0m15.018s
user    0m0.009s
sys     0m0.014s
user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1001
;; connection timed out; no servers could be reached



real    0m15.019s
user    0m0.009s
sys     0m0.014s
user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1112
Server:         2606:4700:4700::1112
Address:        2606:4700:4700::1112#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
;; connection timed out; no servers could be reached



real    0m15.032s
user    0m0.010s
sys     0m0.013s
user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1002
Server:         2606:4700:4700::1002
Address:        2606:4700:4700::1002#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.050s
user    0m0.013s
sys     0m0.009s
user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1113
Server:         2606:4700:4700::1113
Address:        2606:4700:4700::1113#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
;; connection timed out; no servers could be reached



real    0m15.037s
user    0m0.017s
sys     0m0.011s
user@host:~$ time nslookup cloudflare.com 2606:4700:4700::1003
;; connection timed out; no servers could be reached



real    0m15.016s
user    0m0.012s
sys     0m0.016s

Google DNS via hostname

user@host:~$ time nslookup cloudflare.com dns.google
Server:         dns.google
Address:        2001:4860:4860::8888#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:85e5
Name:   cloudflare.com
Address: 2606:4700::6810:84e5


real    0m0.094s
user    0m0.018s
sys     0m0.006s

Cloudflare DNS via hostname

user@host:~$ time nslookup cloudflare.com one.one.one.one
Server:         one.one.one.one
Address:        2606:4700:4700::1111#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m1.096s
user    0m0.013s
sys     0m0.013s
user@host:~$ time nslookup cloudflare.com 1dot1dot1dot1.cloudflare-dns.com
Server:         1dot1dot1dot1.cloudflare-dns.com
Address:        2606:4700:4700::1001#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m0.078s
user    0m0.014s
sys     0m0.010s
user@host:~$ time nslookup cloudflare.com security.cloudflare-dns.com
Server:         security.cloudflare-dns.com
Address:        2606:4700:4700::1112#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m1.112s
user    0m0.026s
sys     0m0.000s
user@host:~$ time nslookup cloudflare.com family.cloudflare-dns.com
Server:         family.cloudflare-dns.com
Address:        1.0.0.3#53

Non-authoritative answer:
Name:   cloudflare.com
Address: 104.16.132.229
Name:   cloudflare.com
Address: 104.16.133.229
Name:   cloudflare.com
Address: 2606:4700::6810:84e5
Name:   cloudflare.com
Address: 2606:4700::6810:85e5


real    0m4.072s
user    0m0.022s
sys     0m0.009s

Sometimes it works fine, but 95% of the time I see delays or no response. Sometimes I get partial responses. I’m unable to figure out what exactly is the issue.

2

Duplicate of Cloudlare DNS - `nslookup` fails for IPv6 DNS sometimes, but always works for IPv4 DNS

3

Hi! Could you add a traceroute / mtr to the v6 endpoints that are not working for you? The v4 and v6 should be routed to the same PoP, so I suspect it might be some issue on the path.

4

Sure @mvavrusa! Will add mtr results. Would it be possible for you to combine this thread and Cloudlare DNS - `nslookup` fails for IPv6 DNS sometimes, but always works for IPv4 DNS? Because @milk, @user21517 and I have had some discussions in that thread. Akismet had marked this thread as spam and hid it initially and that’s when I made a new thread.

5

Hey @mvavrusa!

Any updates?

6

I don’t know how to combine a thread, maybe you can close this and continue in the other one?

8

I don’t know how to combine a thread, maybe you can close this and continue in the other one?

Sure @mvavrusa! I don’t have an option to close this thread. But let’s continue on Cloudlare DNS - `nslookup` fails for IPv6 DNS sometimes, but always works for IPv4 DNS.

9

This topic was automatically closed 30 days after the last reply. New replies are no longer allowed.