How come a misconfigured /etc/resolv.conf affects su or ssh?

Question

I have a Rhel 5 VM normally connected to an ldap service and today I discovered that ssh and su were broken. The shell would simply hang while trying either of these commands. I was only able to login as root via console.

ssh was interrupted after the password was accepted (could be seen from /var/log/secure), more specifically at this stage:

debug1: Next authentication method: password
xxxxxxx@xxxxxx's password:
debug2: we sent a password packet, wait for reply
debug1: Authentication succeeded (password).
debug1: channel 0: new [client-session]
debug2: channel 0: send open
debug1: Entering interactive session.

Switching to any local user via su was also impossible although /var/log/secure begged to differ.

As far as ssh is concerned, UseDNS option (/etc/ssh/sshd_config) was commented so I think it's value was 'no'.

And multiple commands (ps, id, su, httpd ..) were generating this error either in /var/log/secure or /var/log/messages

nss_ldap: failed to bind to LDAP server ldap://ldap-bla.bla.bla:###: Can't contact LDAP server 

After sometime I realized that /etc/resolv.conf was misconfigured. I fixed it and the problem solved.

However, I'd appreciate it greatly if somebody could guide me to the understanding of this issue. I can partly see that being unable to reach the ldap server may have affected everything involving remote connections or users but I'd like to know exactly why su to a local user would also be impossible. And how it could've been solved without fixing the ldap. Would removing ldap from nsswitch.conf help?

It was like this:

[root@xxxxxx ~]# grep -i ldap /etc/nsswitch.conf 
passwd:     files sss ldap
shadow:     files sss ldap
group:      files sss ldap
netgroup:   files sss ldap
automount:  files sss ldap
sudoers:  files ldap

Thanks in advance to anybody who'd have the time to reply.