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1.1.3. Endpoint to Security Gateway in Tunnel Mode

1.1.3. Endpoint to Security Gateway in Tunnel Mode​

+-+-+-+-+-+ +-+-+-+-+-+ | | IPsec | | Protected |Protected| tunnel |Tunnel | Subnet |Endpoint |<------------------------>|Endpoint |<--- and/or | | | | Internet +-+-+-+-+-+ +-+-+-+-+-+

       Figure 3:  Endpoint to Security Gateway Tunnel

In this scenario, a protected endpoint (typically a portable roaming computer) connects back to its corporate network through an IPsec- protected tunnel. It might use this tunnel only to access information on the corporate network, or it might tunnel all of its traffic back through the corporate network in order to take advantage of protection provided by a corporate firewall against Internet-based attacks. In either case, the protected endpoint will want an IP address associated with the security gateway so that packets returned to it will go to the security gateway and be tunneled back. This IP address may be static or may be dynamically allocated by the security gateway. In support of the latter case, IKEv2 includes a mechanism (namely, configuration payloads) for the initiator to request an IP address owned by the security gateway for use for the duration of its SA.

In this scenario, packets will use tunnel mode. On each packet from the protected endpoint, the outer IP header will contain the source IP address associated with its current location (i.e., the address that will get traffic routed to the endpoint directly), while the inner IP header will contain the source IP address assigned by the security gateway (i.e., the address that will get traffic routed to the security gateway for forwarding to the endpoint). The outer destination address will always be that of the security gateway, while the inner destination address will be the ultimate destination for the packet.

In this scenario, it is possible that the protected endpoint will be behind a NAT. In that case, the IP address as seen by the security gateway will not be the same as the IP address sent by the protected

Kaufman, et al. Standards Track [Page 8] RFC 5996 IKEv2bis September 2010

endpoint, and packets will have to be UDP encapsulated in order to be routed properly. Interaction with NATs is covered in detail in Section 2.23.

1.1.3. A subnet may make all external accesses through a remote​

security gateway using an IPsec tunnel, where the addresses on the subnet are routed to the security gateway by the rest of the Internet. An example would be someone's home network being virtually on the Internet with static IP addresses even though connectivity is provided by an ISP that assigns a single dynamically assigned IP address to the user's security gateway (where the static IP addresses and an IPsec relay are provided by a third party located elsewhere).

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