H3C Technologies H3C S12500 Series Switches - Manual (Page 189)

176
431B
Constructing VPN
Figure 76 Network diagram
As shown in
815H
Figure 76 , Site 1 and Site 2 both belong to VPN 1 and are located in different cities. Using
a GRE tunnel can connect the two VPN sites across the WAN.
318B
Protocols and standards
• RFC 1701, Generic Routing Encapsulation (GRE)
• RFC 1702, Generic Routing Encapsulation over IPv4 networks
• RFC 2784, Generic Routing Encapsulation (GRE)
160B
Configuring a GRE over IPv4 tunnel
Follow these guidelines when you configure a GRE over IPv4 tunnel:
• You must configure the tunnel source address and destination address at both ends of a tunnel, and
the tunnel source or destination address at one end must be the tunnel destination or source address
at the other end.
• Local tunnel interfaces using the same encapsulation protocol must not have the same tunnel source
and destination addresses.
• You can enable or disable the checksum function at both ends of a tunnel.
{
If checksum is enabled at the local end but not at the remote end, the local end calculates the
checksum of a packet to be sent but does not check the checksum of a received packet.
{
If checksum is enabled at the remote end but not at the local end, the local end checks the
checksum of a received packet but does not calculate the checksum of a packet to be sent.
• You can use the following methods to configure a route to a destination over the GRE tunnel:
{
Configure a static route, using the destination address of the original packet as the destination
address of the route and the address of the peer tunnel interface as the next hop.
{
Enable a dynamic routing protocol on both the tunnel interface and the interface connecting
the private network, so the dynamic routing protocol can establish a routing entry with the
tunnel interface as the outgoing interface.
• The IP address of the tunnel interface and the tunnel destination address configured on the tunnel
interface must be in different subnets.