[SGVLUG] using SSH from a non-confirmable client -- how?

[Jeff Carlson]

Emerson, Tom wrote:
> Nov  2 15:16:08 osnut sshd[25833]: reverse mapping checking
> getaddrinfo for h-64-236-243-16.twi.com failed - POSSIBLE BREAKIN
> ATTEMPT!

It's not your gateway, it's your DNS server.  Your A record doesn't 
match your PTR.  Here:

$ host 64.236.243.16
16.243.236.64.in-addr.arpa domain name pointer h-64-236-243-16.twi.com.
$ host h-64-236-243-16.twi.com
Host h-64-236-243-16.twi.com not found: 3(NXDOMAIN)

Your sshd at home is configured to require these two to match.  I will 
bet there is an A record in your company's DNS that does match your IP, 
but obviously, your PTR is this generic h-#-#-#-# thing.  Your sshd is 
configured to look up the IP, then look up the name that previous lookup 
returned.  This can also be done in tcp_wrappers using the PARANOID 
setting.  Check /etc/hosts.allow and /etc/hosts.deny.  If there is such 
a PARANOID setting, just insert this into hosts.allow ahead of the 
PARANOID line:

sshd: 64.236.243.16

Otherwise check the sshd_config(5) man page and look for paranoid DNS 
operation.

You might be able to cheat by putting an entry in /etc/hosts.  That can 
usually bypass DNS if the subsystem is actually doing a gethostby* 
syscall.  I'm not sure if sshd uses that libc method or specifically 
relies on DNS.