HP FlexNetwork MSR2003 Configuration Manual page 350

To establish a hub-hub tunnel:
The hub checks whether a tunnel to each peer hub exists. If not, the hub sends a tunnel
establishment request to the peer hub.
To establish a spoke-spoke tunnel:
In a full-mesh network, when a spoke receives a data packet but finds no tunnel for
forwarding the packet, it sends an address resolution request to the server. After receiving
the resolved address, the spoke sends a tunnel establishment request to the peer spoke.
2. The receiver saves tunnel information in the request and sends a response to the sender.
Figure 145 Tunnel establishment process
Route learning and packet forwarding
ADVPN nodes use the following methods to learn private routes:
•
Static or dynamic routing—It must be configured for private networks and ADVPN tunnel
interfaces to ensure connectivity among private networks. A dynamic routing protocol discovers
neighbors, updates routes, and establishes a routing table over ADVPN tunnels. From the
perspective of private networks, ADVPN tunnels are links that connect different private
networks. The routing protocol exchanges routes between hub and hub, and between hub and
spoke. It does not directly exchange routes between spoke and spoke.
When a spoke receives a packet destined to a remote private network, it performs the following
operations to forward the packet:
a. Locates the private next hop from the routing table.
b. Uses the private next hop to obtain the corresponding public address from the VAM server.
c. Sends the packet to the public address over the ADVPN tunnel.
Full-mesh and hub-spoke structures are determined by routing. If the next hop is a spoke, the
structure is full-mesh. If the next hop is a hub, the structure is hub-spoke.
•
Registration and query from the VAM server—VAM clients register information about the
connected private networks on the VAM server.
When a spoke receives a packet destined to a remote private network, it performs the following
operations to forward the packet:
a. Sends the destination address of the packet to the VAM server.
b. Queries the VAM server for information about the ADVPN node (public and private
addresses of the node) connected to the remote private network.
c. Generates a route to the remote private network through the ADVPN node.
d. Sends the packet to the public address of the ADVPN node over the ADVPN tunnel.
If both methods are used, the spoke sends both the private next hop and the destination address of
the packet to the VAM server. The VAM server preferentially obtains the private network according to
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