MPLS – AToM (Any Transport of MPLS) and EoM (Ethernet over MPLS) overview, very high level review of technology, some configuration examples as well!


So this is getting pretty out of bounds of what I know / have worked with at all, however I  wanted to make a quick note on these technologies so I have reference to them, those two being AToM (Anything over MPLS) and EoM (Ethernet over MPLS).

From my understanding AToM is for more dated Layer 2 technologies like Frame-Relay or ATM (Serial Connections) to an MPLS Provider Edge, whereas EoM is still Layer 2 but Ethernet to the Provider Edge, meaning of course the MPLS Provider Edge is the Transport for this Layer 2 traffic over a Layer 3 (technically) Label Switched Network.

Unlike L2TP these are both MPLS Based Layer 2 Transport technologies, these are both considered “Point to Point” Protocols, and are essentially like plugging into a Provider “Cloud” as though it were a giant switch / Ethernet segment.

Given my new understanding of EoM, I will lab it in another section (or attempt to).

AToM Terminology explained

  • AC = Attachment Circuit = Connection from CE to PE that may be a Layer 2 tech like Frame-Relay or ATM traffic
  • PSN = Packet Switched Network = “Pseudowire” = CE to CE communication over an MPLS meaning a Pseudo-Layer 2 connection via MPLS
  • Target LDP Session = Two labels are specifically created for communication for AToM communication
  • VC Label = BoS Label used in AToM Session, identifies Egress PE device to use (where the CE is that needs this packet)
  • Tunnel Label = Regular MPLS Label to allow traffic to be normally Packet Switched
  • P.I.D / PW ID = Psuedowire ID = Created to identify traffic in cloud belonging to a specific Target LDP Session

AToM Configuration explained – Not able to configure on current lab

I might come back to lab this some day as my current routers only support FastEthernet and Ethernet cards in the slots, and I won’t be building a new MPLS network for demonstration, but the configuration is extremely simple:

PE Router

psuedowire-class (name)
encapsulation mpls

CE Router

int s0/0
encapsulation hdlc
xconnect 100 pw-class (name)

The # 100 is a “psuedowire ID #” that would match on both the CE and PE devices.

Ethernet over MPLS overview

This was not included in instructor led material so I am digging into Cisco documentation for this info, EoM is a variation of AToM, and actually since it seems possible to lab I am going to attempt to lab it on my existing MPLS Lab in a new post!

That wraps up my level of knowledge of AToM for MPLS!

The devices in my MPLS Lab in EVE do not support Serial Interfaces, I am not going to go out of my way to build a new MPLS cloud for Frame-Relay / ATM concepts, so I will leave it at just knowing the configuration and what AToM does!

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