Carrier Scenario

Site-to-Site VPN

IPsec provides security protection for any IP-based communications. It is applicable to both the traditional fixed network and the mobile network such as Long Term Evolution (LTE). Regardless of the fixed network or mobile network, most IPsec applications in the carrier scenario are site-to-site VPN and GRE over IPsec.

The site-to-site VPN, also known as a gateway-to-gateway VPN, ensures security of IP traffic between two gateways. Figure 1 shows the typical networking.

Figure 1 Networking of the site-to-site VPN

The site-to-site VPN can be flexibly deployed. When a NAT device exists between two IPsec gateways, the IPsec NAT traversal is supported.

GRE over IPsec

IPsec cannot encapsulate multicast, broadcast, or non-IP packets. Therefore, when transmitting the preceding packets over the IPsec VPN, IPsec encapsulates the packets as IP packets using GRE and then encapsulates the packets as IPsec packets, as shown in Figure 2.

Figure 2 GRE over IPsec networking

Various applications are based on GRE over IPsec, for example, Border Gateway Protocol (BGP), Label Distribution Protocol (LDP), Open Shortest Path First (OSPF), Intermediate System to Intermediate System (IS-IS), and IPv6. Based on the same principle, these applications encapsulate packets as IP packets using GRE and then transmit the packets over IPsec tunnels, as shown in Figure 3, Figure 4, and Figure 5.

Figure 3 Networking of EBGP over GRE over IPsec

Figure 4 Networking of OSPF over GRE over IPsec, IS-IS over GRE over IPsec, LDP over GRE over IPsec, and IBGP over GRE over IPsec

Figure 5 Networking of IPv6 over GRE over IPsec