source nat pool

Use this command to configure the overloaded IPv4 address or an IPv6 range to which the web cache client will be natted.

Syntax

Parameters

Defaults

None.

Mode

Configuration command, Web-cache Configuration mode

Usage

This command configures the TWCB source NAT pool component of the TWCB source and destination NAT feature. The configuration of TWCB source and destination NAT allows the client, TWCB router, and web cache server to reside anywhere in the network and still provide for the forwarding of an HTTP request from the client to the web cache server. TWCB source and destination NAT also provides for the reverse forwarding from the web cache server to the client, assuring that the packet flow will pass through the TWCB router.

Standard TWCB operation requires that a cache server have a route back to the client through the TWCB router. Client addresses are often unknown to the cache server. The TWCB source and destination NAT feature addresses these two issues. TWCB source NAT, configured using this command, provides a TWCB public facing source address as the TWCB router forwards the packet on to the web cache server, assuring that the web cache server will reverse flow the packet back through the TWCB router. Destination NAT provides a public facing TWCB router web cache address from the perspective of the client and is configured using destination ip.

First configure destination NAT by assigning an access list containing a range of public facing IP addresses the client will use to reach the TWCB router web cache. See destination ip for destination NAT configuration details.

When the HTTP request reaches the TWCB router, TWCB determines the web cache server that will process the request. Before it forwards the packet on to the web cache server, it selects a public facing source address configured using this command. When the web cache server forwards the reverse flow back to the client, it uses this public source NAT address as its destination. When the reverse packet arrives at the TWCB router, it uses the original client request‘s destination IP address as the packet source and forwards the server response to the client.

By default, source natting of a TWCB router web cache address does not occur.

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.

The “no” form of this command removes the specified web cache IPv4 source NAT pool or IPv6 source NAT IP address and prefix length.