NAT and age

Hi,

I'd like to understand how aging of NAT entries work. I'm currently
struggling with my NAT table filling up and never expiring any entries.

I'm using only two rules:
map en0 10.10.0.0/16 -> a.b.c.d/32 age 2
rdr en0 a.b.c.d port 80 -> 10.10.20.4 port 80

One machine on the private net does *a lot* of DNS queries and fills up
the NAT table pretty quickly with entries like:
MAP 10.10.10.3 51019 <- -> a.b.c.d 51019 [e.f.g.h 53]

No entry ever expires as I can tell from an 'ipnat -s' thus when 30000
lines have been added, no new connections will be handled. Neither by
the MAP nor by the RDR statement. I have to manually flush the table
('ipnet -F') first to make things work again.

I'm using a build of IPFilter v4.1.13, compiled with default options,
running on AIX 5.3TL05.

Any ideas welcome.

Thanks,
Christian