Any Transport Over MPLS (AToM)

Any Transport over MPLS (AToM) will transport layer 2 frames over a 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 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 router. This ISP only has one customer that has a 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 router 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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