6.3.d Implement and troubleshoot IPv4 network address translation

6.3.d [ii] NAT ALG

Network Address Translation (NAT) performs translation service on any TCP/ UDP traffic that does not carry source and/ or destination IP addresses in the application data stream (ie: http, TFTP, telnet, NTP, NFS, rlogin, rsh, rcp). Specific protocols that do embed IP address information within the payload require support of an application level gateway (ALG). NAT performs translation service on any TCP/ UDP traffic that does not carry the source and destination IP addresses in the application data stream. These protocols include HTTP, TFTP, telnet, Network Time Protocol (NTP), Network File System (NFS ), remote login (rlogin), remote shell (rsh ) protocol, and remote copy (rcp). Specific protocols that do embed IP the address information within the payload require support of an ALG.

NAT with an ALG will translate packets from applications that do not use H. 323, as long as the applications use port 1720.

http://www.cisco.com/en/US/technologies/tk648/tk361/tk438/technologies_white_paper09186a00801af2b9.html

http://www.cisco.com/en/US/docs/ios-xml/ios/ipaddr_nat/configuration/15-0s/iadnat-applvlgw.html
Adam, Paul (2014-07-12). All-in-One CCIE V5 Written Exam Guide (Kindle Locations 6004-6011).  . Kindle Edition.