R0106-HP MSR Router Series Layer 3 - IP Services Configuration Guide(V7)

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Tunnel establishment phase
A spoke can establish permanent tunnels to any number of hubs. Hubs in an ADVPN domain must
establish permanent tunnels.
Figure 134 Tunnel establishment process
Figure 134 shows the tunnel establishment process:
1. The initiator originates a tunnel establishment request.
{ To establish a hub-spoke tunnel:
The spoke checks whether a tunnel to each hub exists. If not, the spoke sends a tunnel
establishment request to the hub.
{ 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 and then, after receiving the
resolved address, 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.
Route learning and packet forwarding
Static or dynamic routing must be configured for private networks and ADVPN tunnel interfaces to
achieve 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 common private 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 steps to
forward the packet:
1. Finds the private next hop from the routing table.
2. Uses the private next hop to obtain the corresponding public address from the VAM server.
3. 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.