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NHC—NHRP client, a spoke device in the mGRE network. Typically, it is the gateway of a
branch network. An NHC does not forward data received from other mGRE nodes.
mGRE obtains dynamic public addresses of NHCs through their private addresses to establish
mGRE tunnels and forward packets. The public address is the IP address of the interface connected
to the Internet. The private address is the IP address of the mGRE tunnel interface.
An NHC registers its public and private addresses with the NHS and it registers its public address
whenever the public address changes. An NHC obtains the current public address of a peer NHC
from the NHS through NHRP, so the two NHCs can establish an mGRE tunnel over the Internet.
mGRE operation procedure
The mGRE operation includes the following phases:
Registration.
Tunnel establishment.
Route learning and packet forwarding.
Registration
As shown in Figure 1, the registration process is as follows:
1. The NHC sends a registration request to the NHS.
2. After the NHS receives the request, it performs the NHRP packet authentication key and GRE
key matching. If both keys are matched, registration succeeds. The NHS sends a registration
success message to the NHC.
Figure 1 Registration process
Tunnel establishment
mGRE networks support the following types of networking:
Full-mesh network—NHCs can establish tunnels between each other for direct
communication. The NHS acts as the routing information exchange center.
NHC NHS
1) Registration request
2) Registration acknowledgment
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