Web OS 10.0 Application GuideChapter 7: Filtering n 191212777-A, February 2002Network Address TranslationNetwork Address Translation (NAT) is an Internet standard that enables an Alteon Web switchto use one set of IP addresses for internal traffic and a second set of addresses for external traf-fic. Alteon Web switches use filters to implement NAT.NAT serves two main purposes: Provides a type of firewall by hiding internal IP addresses and increases network security. Enables a company to use more internal IP addresses. Since they’re used internally only,there’s no possibility of conflict with public IP addresses used by other companies andorganizations.In the following NAT examples, a company has configured its internal network with private IPaddresses. A private network is one that is isolated from the global Internet and is, therefore,free from the usual restrictions requiring the use of registered, globally unique IP addresses.With NAT, private networks are not required to remain isolated. NAT capabilities within theswitch allow internal, private network IP addresses to be translated to valid, publicly adver-tised IP addresses and back again. NAT can be configured in one of the following two ways: Static NAT provides a method for direct mapping of one predefined IP address (such as apublicly available IP address) to another (such as a private IP address) Dynamic NAT provides a method for mapping multiple IP addresses (such as a group ofinternal clients) to a single IP address (to conserve publicly advertised IP addresses)Alteon Web switches use filters to implement NAT.Static NATThe static NAT (non-proxy) example requires two filters: one for the external client-sideswitch port, and one for the internal, server-side switch port. The client-side filter translatesincoming requests for the publicly advertised server IP address to the server’s internal privatenetwork address. The filter for the server-side switch port reverses the process, translating theserver’s private address information to a valid public address.
