Any Transport Over MPLS (AToM)

Lesson Contents

Any Transport over MPLS (AToM) will transport layer 2 frames over an MPLS (Multiprotocol Label Switching) network. This will allow service providers to connect layer 2 networks of customers transparently by using their MPLS backbone. AToM can transport the following:

  • ATM AAL5
  • ATM Cell Relay
  • Ethernet
  • Frame Relay
  • PPP
  • HDLC

I will give you an example of how to configure AToM to transport Ethernet over the MPLS backbone. We will use the following topology to do this:

MPLS Atom Ethernet

Above, you see a small MPLS backbone that consists of the PE1, P, and PE2 routers. This ISP only has one customer that has an HQ and Branch. The customer wants to have the HQ and Branch router to be in the same layer 2 segment.


First, we will enable OSPF to advertise the loopback interfaces. These will be used as the router ID for MPLS LDP:

PE1(config)#router ospf 1
PE1(config-router)#network area 0
PE1(config-router)#network area 0
P(config)#router ospf 1
P(config-router)#network area 0
P(config-router)#network area 0
P(config-router)#network area 0
PE2(config)#router ospf 1
PE2(config-router)#network area 0
PE2(config-router)#network area 0

Now we will enable MPLS LDP on the interfaces connecting the PE1, P, and PE2 routers:

PE1(config)#interface fastEthernet 0/1
PE1(config-if)#mpls ip
P(config)#interface fastEthernet 0/0
P(config-if)#mpls ip

P(config)#interface fastEthernet 0/1
P(config-if)#mpls ip 
PE2(config)#interface fastEthernet 0/0
PE2(config-if)#mpls ip

Just to be sure let’s verify that we have LDP neighbors:

P#show mpls ldp neighbor | include Peer
    Peer LDP Ident:; Local LDP Ident
    Peer LDP Ident:; Local LDP Ident

That seems to be the case! Now we can configure AToM so that the HQ and Branch routers are able to reach each other:

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Forum Replies

  1. Thank you, Rene, for what you do. I like very much the way you simplify complicated things. Keep doing great stuff !!!

  2. Rene! its a great walkthrough tutorial but little help required. which ios version to use? 12.4 does not support “xconnect 13 encapsulation mpls” command. waiting for your reply

  3. Hi Babar,

    I think the problem is not the 12.4 IOS version but the platform you are using. I’m not 100% sure but I believe in GNS3 you can only do it on the 7200 router, not the 3600/3700 series. I haven’t checked it on my 1841 and 2811 routers but I can take a look if you want.


  4. Thanks Rene,
    I have changed the ios to 12.4.9T with the platform 7200. Still its not working…
    Any ideas??

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