From IPFlow Netflow Collector

MPLS ATOM (Any Transport Over MPLS) Example

This is a simple example of MPLS ATOM configuration on Cisco routers (using Dynamips and GNS3).

Author: Christophe Fillot - 02-Nov-2007

Table of contents




A customer wants to establish an HDLC link between two of its routers (CE1 and CE2), through a MPLS backbone (P,PE1 and PE2).

Configuring ATOM

This is very simple (the VC ID 100 is used in this example):

On PE1:

interface Serial1/0
 description To CE1
 no ip address
 serial restart-delay 0
 xconnect 100 encapsulation mpls  ! = Lo0 of PE2

On PE2:

interface Serial1/0
 description To CE2
 no ip address
 serial restart-delay 0
 xconnect 100 encapsulation mpls  ! = Lo0 of PE1

IOS configurations

IOS configurations for Provider routers:

  • P (
  • PE1 (
  • PE2 (

IOS configurations for Customer routers:

  • CE1 (
  • CE2 (

Output of some commands

PE1#sh mpls l2 vc

Local intf     Local circuit              Dest address    VC ID      Status    
-------------  -------------------------- --------------- ---------- ----------
Se1/0          HDLC                    100        UP        

PE1#sh mpls l2 vc de
Local interface: Se1/0 up, line protocol up, HDLC up
  Destination address:, VC ID: 100, VC status: up
    Next hop:
    Output interface: Fa0/0, imposed label stack {16 19}
  Create time: 00:24:08, last status change time: 00:24:04
  Signaling protocol: LDP, peer up
    MPLS VC labels: local 19, remote 19 
    Group ID: local 0, remote 0
    MTU: local 1500, remote 1500
    Remote interface description: To CE2
  Sequencing: receive disabled, send disabled
  VC statistics:
    packet totals: receive 198, send 197
    byte totals:   receive 16121, send 15456
    packet drops:  receive 0, seq error 0, send 0

PCAP captures

The PCAP captures show how the packets are sent on the HDLC link and how they are transmitted on the MPLS core:

Here are the screenshots from Wireshark:

As you can see, Wireshark is not able to recognize that the packets contain encapsulated HDLC frames after the MPLS label stack. The MPLS labels are {16 19} (as shown with "show mpls l2 vc detail"). The first label (16) corresponds to PE2 loopback (, and the second label to the L2VPN itself (from PE2 point-of-view).

Dynamips/Dynagen/GNS3 configuration

You can use this configuration file ( directly with Dynagen or GNS3. Change the working directory and Cisco IOS image path to match your needs.