[ale] weirdness with slow ssh connections (IPv6 related?)

[Steven A. DuChene]

I am working on a project with 50 - 70 servers in the AT&T data center
on University. They have either RHEL5U3 or CentOS5U3 on the systems.
I have DNS configured with the normal bind 9 packages that come with
CentOS5U3. My problem is when using ssh to get between the systems
if i use the short name for a system it takes a long time to get to
a shell prompt on the remote system. If I use the fully qualified
domain name or the IP address of I use a "-4" with the short name
I get to a shell prompt immediately. So to illustrate:

root at adm #  ssh new75

takes a LONG time to get shell prompt.

Any of the following get me a shell prompt almost immediately:

root at adm #  ssh -4 new75

root at adm #  ssh new75.wholedomain.here

root at adm #  ssh 10.4.5.6   (IP address of new75 system)

Since the "-4" option seems to have a positive effect I have gone
to each system and made sure the IPv6 kernel modules are not loaded
and the network file in /etc/sysconfig/ has the following line in
it:

NETWORKING_IPV6=no

but that made little or no difference to the problem. The lines
I added to the /etc/modprobe.conf file look like this:

alias net-pf-10 off
alias ipv6 off

I believe it some strange interaction problem between IPv6 and DNS
but I do not have a clear plan on what to try next.

Any suggestions?
--
Steven DuChene