[nsd-users] What is the selection order of forward-first NSs? sequential? random? IPv6 before/after IPv4?

George Thessalonikefs george at nlnetlabs.nl
Wed Jun 9 14:50:13 UTC 2021

Hi pgnet(?),

I think you posted on the wrong mailing list :)
I'll reply here and include unbound-users also.

If you want to reply further please drop nsd-users and let us continue 
the discussion only on the unbound-users mailing list as to not generate 
noise here.

On 07/06/2021 21:31, PGNet Dev via nsd-users wrote:
> On my server, I config
>      cat /etc/resolv.conf
>          nameserver
> , where unbound 1.13.1 listens @
>      server:
>          interface: at 53
> if I set up forward-first in unbound config,
>      forward-zone:
>          name: "."
>              forward-first: yes
>              forward-addr: <server.1.ipv.6>
>              forward-addr: <server.1.ipv.4>
>              ...
>              forward-addr: <server.n.ipv.6>
>              forward-addr: <server.n.ipv.4>
> what's the order policy for those forward-addr's?
> Is the forward-addr used randomly, or sequentially, selected from that 
> list?
Randomly between the fastest servers (in the <400ms band). Unbound will 
keep probing the other servers to keep updated metrics for them in case 
they become fast enough (<400ms). You can read more about it at 

> Is there any unbound preference for IPv4 vs IPv6 forward-addrs?
There are the 'prefer-ip4:' and 'prefer-ip6:' options if you want to do 

> Does the preference respect /etc/gai.conf?

Best regards,
-- George
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