If you're using LDAP with those options in /etc/conf.d/slapd
OPTS="-h 'ldap://127.0.0.1 ldaps://foo.bar.tld:23523'"
a missconfigured /etc/resolv.conf could be fatal. Your slapd would not run and die with
slapd[12876]: daemon: getaddrinfo() failed: Temporary failure in name resolution
A possible solution is to resolve your hostname yourself. Just put a $IP $HOSTNAME of yourself in the /etc/hosts. That should be very safe.
Another point is that if your name resolution is broken ssh will have got problems with local users if it cannot reach the ldap daemon because it is down.
Connection closed by remote host
This only happens if you send a public key to authorize yourself. To fix this issue try to don't send any public key
ssh foo.bar.tld -l localuser -o PubkeyAuthentication=no
Thanks to KillerFox for reproducing these things.