How to disable DNS lookups?

Roland C. Dowdeswell Roland.Dowdeswell at twosigma.com
Wed Jul 26 04:05:21 CEST 2017


On Tue, Jul 25, 2017 at 11:20:57PM +0200, u-hd-phes at aetey.se wrote:
>

> Given that SRV records as a matter of fact are defined via A[AAA] records,
> (and given that A lookups historically _are_ interposed by /etc/hosts)
> what says that /etc/hosts are to be ignored if an A lookup happens as
> a consequence of an SRV one?

Actually, I do not think that A lookups historically are interposed by
/etc/hosts.

I think that it is more accurate to say that historically there have been
functions called gethostbyname(3) and getaddrinfo(3) which mediated by
the definitions in /etc/nsswitch.conf choose whether to do files, DNS,
LDAP, YP, etc.  In all of the implementations that I've seen, once you
call into one of those modules, it will either return an entire answer
back up or fail which allows the NSS framework to pass control to the
next module.  In some cases, mostly with YP there are ways to mix the
modules a bit but those are mostly used for the passwd and group maps
rather than the host map.

-- 
    Roland C. Dowdeswell


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