Gre Application Scenarios - HPE FlexNetwork 10500 Series Configuration Manual

As shown in
follows:
1. After receiving an IPv6 packet from the interface connected to IPv6 network 1, Device A
processes the packet as follows:
a. Looks up the routing table to identify the outgoing interface for the IPv6 packet.
b. Submits the IPv6 packet to the outgoing interface—the GRE tunnel interface Tunnel 1.
2. Upon receiving the packet, the tunnel interface encapsulates the packet with GRE and then
with IPv4. In the IPv4 header:
The source address is the tunnel's source address (the IP address of interface

GigabitEthernet 1/0/1 of Device A).
The destination address is the tunnel's destination address (the IP address of interface

GigabitEthernet 1/0/1 of Device B).
3. Device A looks up the routing table according to the destination address in the IPv4 header, and
forwards the IPv4 packet out of the physical interface (GigabitEthernet 1/0/1) of the GRE
tunnel.
4. When the IPv4 arrives at the GRE tunnel destination Device B, Device B checks the destination
address. Because the destination is Device B itself and the protocol number in the IP header is
47 (the protocol number for GRE), Device B submits the packet to GRE for de-encapsulation.
5. GRE first removes the IPv4 header, and then checks the packet sequence number. After GRE
finishes the checking, it removes the GRE header, and submits the payload to the IPv6 protocol
for forwarding.
NOTE:
GRE encapsulation and de-encapsulation can decrease the forwarding efficiency of tunnel-end
devices.

GRE application scenarios

The following shows typical GRE application scenarios:
Connecting networks running different protocols over a single backbone
Figure 102 Network diagram
IPv6 network 1
Device A
IPv4 network 1
As shown in
and IPv4 network 2 are IPv4 networks. Through the GRE tunnel between Device A and Device B,
IPv6 network 1 can communicate with IPv6 network 2 and IPv4 network 1 can communicate with
IPv4 network 2, without affecting each other.
Figure 101, an IPv6 protocol packet traverses an IPv4 network through a GRE tunnel as
Internet
GRE tunnel
Figure 102, IPv6 network 1 and IPv6 network 2 are IPv6 networks, and IPv4 network 1
IPv6 network 2
Device B
IPv4 network 2
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