cache-max-ttl

[Paul Wouters]

Your suggestion seems to be what I would expect unbound to do.

Paul

Sent from mobile device

> On Dec 1, 2018, at 11:12, Daisuke HIGASHI via Unbound-users <unbound-users at nlnetlabs.nl> wrote:
> 
> Hi,
> 
>   cache-max-ttl option defines upper-bound of RRsets TTL
> but initial TTL value _shown_ by Unbound’s response is original TTL e.g.:
> 
> original TTL: 86400
> cache-max-ttl: 300
> 
>  1. TTL value just after RRsets cached: 86400
>  2. TTL value after 100 seconds: 86300
>  3. TTL value after 299 seconds: 86101
>  4. TTL value after 300 seconds: (expired)
> 
>  This is documented behavior, but problematic if there is caching DNS proxy
> (e.g. home router) between Unbound and client — The DNS proxy will cache
> RRsets with large (86400) TTL and hold them long time regardless of
> cache-max-ttl.
> 
>  I think that Unbound's implementation should be changed so that
> cache-max-ttl defines also upper-bound of initial TTL shown
> by Unbound's response just like:
> 
>  1. TTL value just after RRsets cached: 300
>  2. TTL value after 100 seconds: 200
>  3. TTL value after 299 seconds: 1
>  4. TTL value after 300 seconds: (expired)
> 
> A quick hack patch attached.
> Is it useful? And is it harmless to existing Unbound deployments?
> 
> Regards,
> -- 
> Daisuke HIGASHI
> <min-ttl.patch>