# [OmniOS-discuss] OpenSSH and reverse DNS

Lauri Tirkkonen lotheac at iki.fi
Tue Nov 29 11:30:17 UTC 2016

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    On Tue, Nov 29 2016 10:47:10 +0100, Olaf Marzocchi wrote:
    > Dear all,
    > Since I upgraded to OpenSSH I have the following problem with DNS:
    > reverse mapping checking getaddrinfo for hostxxx.retail.telecomitalia.it [_ip_] failed - POSSIBLE BREAK-IN ATTEMPT!
    > The remote SSH server has always been OenSSH, the issue appeared when the client (OmniOS) got updated.

    Strange - why would the server suddenly start caring about DNS checks if
    the client was updated?

    > I have no access to the DNS records. I already have a dynamic DNS configured, but the reverse one is out of my reach.
    >
    > I found online possible solutions and I described the issue also here without success: http://superuser.com/questions/1149850/how-to-disable-the-message-reverse-mapping-checking-getaddrinfo-for-xxx-failed
    >
    > "UseDNS no" helped me to be able at least to connect, but still I cannot disable the warning. Since I launch daily rsync backups via cron, I get emails every morning without any real security issue (in my case).

    "UseDNS no" sshd option should indeed resolve this -- my reading of
    both the manual and code is that it prevents sshd from resolving client
    addresses. If you have console access to the server try 'sshd -T | grep
    usedns' to see if it actually is using the correct configuration file.

    I guess that the sshd you're using could also be doing something weird,
    but in stock 7.3p1 remote_hostname is only called from
    auth_get_canonical_hostname, which always seems to get options.use_dns
    from the caller.

    --
    Lauri Tirkkonen | lotheac @ IRCnet

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