glibc

Nathan (ncm) might be thinking of the caching that transpires if you start the nscd
(nameservice 
caching daemon).  It's commonly used on systems with heavyweight lookup regimes (NIS, NIS+, 
LDAP) to prevent system performance from bogging down excessively, by locally caching lookup
of  
hosts, users, groups, services, RPC ports, netgroups, etc. but has the drawback that it
ignores TTL 
values on host lookups.  (That's a sufficient reason to disable host caching in /etc/nscd.conf
.)

The BIND8-derived stub resolver in glibc isn't a huge security risk on most systems despite
its 
haplessly failing to randomise UDP source ports, because the result doesn't get cached.
(Thus, 
sending it poisoned data in an ADDITIONAL SECTION portion of a recursive DNS response doesn't 
do the attacker much good, because the poison gets metaphorically flushed immediately.)  
However, such a system with nscd caching hostnames would have a problem.  (So, Don't Do That, 
Then.)

Rick Moen
rick@linuxmafia.com