TWCB Source NAT

Before the TWCB router forwards the HTTP request to the web cache server, it first selects a source NAT address from the IPv4 source NAT pool or IPv6 source NAT address range defined using the source nat pool command. Using this public facing source NAT address assures that the web cache server reverse packet flow will pass through the TWCB router on its way back to the client.

For IPv4, one or more overloaded public facing IP addresses are assigned to a NAT pool, allowing multiple clients to use the same external address, with NAPT assigning an unused port to differentiate between clients. For IPv6 clients, an IPv6 address and prefix length is specified providing a range of external IP addresses.

The IPv6 address definition requires a prefix length of 111 or less in order to account for the checksum-neutral calculation of the IPv6 client address.