Interface Types

Hello All,

There are two types of interfaces, P2P such as PPP or HDLC, and Multipoint interfaces such as Ethernet, Frame Relay and DMVPN. Am I correct?

On Ethernet-based networks we use ARP for the Layer3-to-Layer2 mapping and thus form the Layer2 frame.

  • What is the equivalent on DMVPN? I know we need to use NHRP for the NBMA-to-Tunnel IPs mapping.
  • Do we also need to form a L2 frame on this type of network?
  • Are these type of options such as Frame-Relay (no longer used) and DMVPN, layer 2 solutions? or Layer 3?

Please explain.


Hello Luis

When speaking about layer 2 technologies, there are indeed two categories of interface types:

  1. Multi-Access - Ethernet is considered multi-access because you can have multiple hosts on a single segment.
  2. Point to point - Serial, HDLC, PPP, and Frame Relay are all considered point to point technologies because they create circuits between two devices.

Frame Relay is a special case, because it can be configured to mimic a multi-access broadcast network to get certain functionalities to work properly, such as dynamic routing protocols. However, because it uses point to point virtual circuits for its functionality, in essence, it is considered a point to point technology.

For clarification, the terms point to point and point to multi-point are used to describe a topology, especially when referring to ways in which Frame Relay can be deployed.

Finally, DMVPN is not considered a P2P or a multi access technology, because it is not an L2 technology, but functions at L3. It is a framework that allows you to create multipoint GRE tunnels. So the term “multipoint” can be used to describe DMVPN only as far as the topology of the GRE tunnels being used to create multiple VPNs between the devices in question.

Note that DMVPN will most often use Ethernet interfaces to terminate the GRE tunnels, so it will simply use the same mechanisms for physical address discovery that Ethernet uses.

All network technologies require some form of frame at L2. You can’t skip a layer of the OSI model as you go along. DMVPN will simply use whatever interface type is used to terminate the GRE tunnels, in most cases this is Ethernet, so an Ethernet frame will be used.

As mentioned before, DMVPN is a Layer 3 technology because it functions with GRE tunnels. Frame relay is a Layer 2 technology.

For more information about DMVPN, take a look at the following lesson as well as the subsequent lessons about DMVPN.

I hope this has been helpful!


1 Like

thanks for the help, good info!