MPLS ATOM

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

Topology

Image:MPLS_ATOM_topo.png


Description

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 10.10.0.2 100 encapsulation mpls  ! 10.10.0.2 = Lo0 of PE2
!


On PE2:

interface Serial1/0
 description To CE2
 no ip address
 serial restart-delay 0
 xconnect 10.10.0.1 100 encapsulation mpls  ! 10.10.0.1 = Lo0 of PE1
!


IOS configurations

IOS configurations for Provider routers:

  • P (http://www.ipflow.utc.fr/configs/MPLS_ATOM/P.cfg)
  • PE1 (http://www.ipflow.utc.fr/configs/MPLS_ATOM/PE1.cfg)
  • PE2 (http://www.ipflow.utc.fr/configs/MPLS_ATOM/PE2.cfg)


IOS configurations for Customer routers:

  • CE1 (http://www.ipflow.utc.fr/configs/MPLS_ATOM/CE1.cfg)
  • CE2 (http://www.ipflow.utc.fr/configs/MPLS_ATOM/CE2.cfg)


Output of some commands

PE1#sh mpls l2 vc

Local intf     Local circuit              Dest address    VC ID      Status    
-------------  -------------------------- --------------- ---------- ----------
Se1/0          HDLC                       10.10.0.2       100        UP        

PE1#sh mpls l2 vc de
Local interface: Se1/0 up, line protocol up, HDLC up
  Destination address: 10.10.0.2, VC ID: 100, VC status: up
    Next hop: 10.0.1.1
    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 10.10.0.2:0 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 (10.10.0.2), and the second label to the L2VPN itself (from PE2 point-of-view).


Dynamips/Dynagen/GNS3 configuration

You can use this configuration file (http://www.ipflow.utc.fr/configs/MPLS_ATOM/mpls_atom.net) directly with Dynagen or GNS3. Change the working directory and Cisco IOS image path to match your needs.