Dynamic Multipoint VPN (CCIE Notes)

Disclaimer: These are my rough cut notes for CCIE Security studies! Not a detailed explanation of DMVPN.

Three components that make up DMVPN:

1. Mulitpoint GRE (mGRE)

  • Tunnel interface having multiple tunnel destinations unlike a point-to-point GRE tunnel that has a single tunnel destination.

2. Next-Hop Resolution Protocol (NHRP)

  • Each router in an NHRP topology acts as either a NHC or a NHS.
  • mGRE uses NHRP for mapping logical/tunnel IP address to physical/real IP addresses.
  • NHC registers its physical-to-tunnel mapped IP address to the NHS and the NHS acts as a database agent which stores all registered mappings and replying to NHC queries.
  • If a NHS does not have a requested entry in its database, it can forward packet to another NHS to see if it has the requested association.

3. Cisco Express Forwarding (CEF)

  • Cisco Express Forwarding (CEF) is a packet-switching technique which provides the ability to switch packets through a device in a very quick efficient way while also keeping the load on the router’s processor low.
  • CEF is made up of two different main components: the Forwarding Information Base (FIB) and the CEF Adjacency Table.

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