[Info-vax] Telnet problems

[jbriggs444]

On Feb 17, 1:03 am, glen herrmannsfeldt <g... at ugcs.caltech.edu> wrote:
> tothestarsby2100 <tomarsin2... at comcast.net> wrote:
>
> (snip)
>
> > Problem is when ever I try to telnet it takes 1 minute and 5 seconds
> > (yes I timed it) before I get a username
> > prompt. This is the only system that I'm  having problems with
>
> The traditional reason for this is that there is no reverse
> lookup (PTR entry) for your address in the DNS.
>
> The server tries to look up your address, to find your hostname
> (such as for the log), and waits for the DNS reply.  When the DNS
> times out, then it does something else (like put in the IP address),
> and that is your delay.

Note that this syndrome is not caused by having no reverse dns
entry.  It is caused by having no working reverse DNS resolution
path to the zone containing the entry.

If, for instance, you have reverse DNS PTR records configured for
for 192.168.0.1 but not for 192.168.0.2, you should be able to telnet
in from either IP address with no delay.  That is because the DNS
resolution process will either succeed quickly or fail (usually with
an NXDOMAIN status) quickly.

It is the middle case that causes problems -- a DNS lookup that
does not succeed quickly and does not fail quickly but just sits
there instead.

A quick test would be to try the lookup yourself.  Ideally the test
should be run prior to using telnet.  Otherwise DNS caching could
taint the results.  [Caching is unlikely to be an issue with a
timed-out lookup, but it's better to eliminate the possibility;
there can be more than one flavor of cache involved]

$ nslookup 1.2.3.4   ! Use the real client IP here