RFC 3022, "Traditional IP Network Address Translator (Traditional NAT)"
RFC 3027, "Protocol Complications with the IP Network Address Translator"
RFC 3235, "Network Address Translator (NAT)-Friendly Application Design Guidelines"
RFC 2663, "IP Network Address Translator (NAT) Terminology and Considerations"
RFC 2694, "DNS Extensions to Network Address Translators (DNS_ALG)"
RFC 2709, "Security Model with Tunnel-Mode IPSec for NAT Domains"
RFC 2391, "Load Sharing Using IP Network Address Translation (LSNAT)"
RFC 2993, "Architectural Implications of NAT"
RFC 3519, "Mobile IP Traversal of Network Address Translation (NAT) Devices"
RFC 3715, "IPSec-Network Address Translation (NAT) Compatibility Requirements"
RFC 3489, "STUN?Simple Traversal of User Datagram Protocol (UDP) Through Network Address Translators (NATs)"
The pf FAQ, ftp://ftp.openbsd.org/pub/OpenBSD/doc/pf-faq.txt
The ipfilter HOWTO, http://www.obfuscation.org/ipf/ipf-howto.html
The pf website, http://www.benzedrine.cx/pf.html
The ipfilter website, http://coombs.anu.edu.au/~avalon/ip-filter.html
The Linux netfilter website, http://www.netfilter.org/
IETF draft-ietf-ipsec-nat-t-ike-08.txt, "Negotiation of NAT-Traversal in the IKE," http://www.ietf.org/internet-drafts/draft-ietf-ipsec-nat-t-ike-08.txt
Cisco.com NAT introduction, http://www.cisco.com/en/US/tech/tk648/tk361/technologies_white_paper09186a0080091cb9.shtml