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Interconnecting Ethernet and Frame-Relay interfaces Using MPLS L2VPN Interworking

June 5, 2012 Leave a comment

One of the MPLS L2VPN or Any Transport over MPLS (AToM) feature is “interworking”, that used to interconnect two different type of interfaces encapsulation.

In this example, we will try to interconnect the customer ethernet interface at one site to the customer frame-relay interface at another site.

The Service Provider core which are consist of PE-2, P-1, P-2 and PE-2 router, are using IGP and MPLS with LDP to distribute labels.

Configuring the customers interface

On customer router CE-1, we are using ethernet interface

interface Ethernet0/2
 ip address 10.0.0.1 255.255.255.0
 !

On customer router CE-2, we are using Serial interface and applying frame-relay encapsulation with DLCI 100.

interface Serial2/0
 no ip address
 encapsulation frame-relay
!
interface Serial2/0.100 point-to-point
 ip address 10.0.0.20 255.255.255.0
  frame-relay interface-dlci 100
!

Configuring AToM Pseudowire at the PE Routers

We are assuming that the Service Provider Core networks already running IGP and MPLS with LDP. In this example we are using OSPF. The important thing is we must have any of the PE Routers Loopback IP address on the routing table and the MPLS label that associated to its.

PE-1#sh ip route 19.19.19.19
Routing entry for 19.19.19.19/32
  Known via “ospf 100“, distance 110, metric 31, type intra area
  Last update from 20.2.4.4 on Ethernet0/0.24, 04:55:09 ago
  Routing Descriptor Blocks:
  * 20.2.3.3, from 19.19.19.19, 04:55:09 ago, via Ethernet0/0.23
      Route metric is 31, traffic share count is 1

PE-1#sh mpls forwarding-table 19.19.19.19
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
2002       3003       19.19.19.19/32   0             Et0/0.23   20.2.3.3

PE-2#sh ip route 2.2.2.2
Routing entry for 2.2.2.2/32
  Known via “ospf 100“, distance 110, metric 31, type intra area
  Last update from 20.5.19.5 on Ethernet0/0.519, 04:56:01 ago
  Routing Descriptor Blocks:
  * 20.6.19.6, from 2.2.2.2, 04:56:01 ago, via Ethernet0/0.619
      Route metric is 31, traffic share count is 1

PE-2#sh mpls forwarding2.2.2.2
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
19008    6013       2.2.2.2/32       0             Et0/0.619  20.6.19.6

In PE-1, we create the pseudowire-class that will used for the customer L2VPN.  The difference from the ordinary AToM pseudowire, is this pseudowire enabling the interworking feature, to connect the different interface type.

pseudowire-class ETH_TO_FR
 encapsulation mpls
 interworking ip
!

Then the pseudowire-class applied to the ethernet interface (Ethernet 0/2) that facing to the customer router (CE-1) and associated to the PE-2 loopback address.

interface Ethernet0/2
 no ip address
 no cdp enable
 xconnect 19.19.19.19 14 pw-class ETH_TO_FR
!

In this example, we are using VC ID number 14.

In the PE-2 router, we do the same thing.

pseudowire-class FR_TO_ETH
 encapsulation mpls
 interworking ip
!

The pseudowire-class then applied to the serial interface (Serial 2/0) that facing to the customer router (CE-2) and associated to the PE-1 loopback address. In this example, we are using DLCI 100.

interface Serial2/0
 no ip address
 encapsulation frame-relay
 frame-relay intf-type dce
!

connect FR_TO_ETH_CONN Serial2/0 100 l2transport
 xconnect 2.2.2.2 14 pw-class FR_TO_ETH
 !
!

Now we verify on the PE-1 wether the AToM pseudowire for the customer has created or not.

PE-1#sh mpls l2transport vc 14 detail | i (up|LDP|label)
Local interface: Et0/2 up, line protocol up, Ethernet up
  Destination address: 19.19.19.19, VC ID: 14, VC status: up
    Output interface: Et0/0.23, imposed label stack {3003 19014}
  Signaling protocol: LDP, peer 19.19.19.19:0 up
    Targeted Hello: 2.2.2.2(LDP Id) -> 19.19.19.19
    Status TLV support (local/remote)   : enabled/supported
      Last local  LDP TLV    status sent: no fault
      Last remote LDP TLV    status rcvd: no fault
    MPLS VC labels: local 2014, remote 19014
    Group ID: local 0, remote 0

We see that the AToM pseudowire for the customer  has created and the VC (Virtual Circuit) status is Up.  Label 2014 is allocated for the pseudowire.

PE-1#sh mpls forwarding-table labels 2014
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
2014       No Label   l2ckt(14)        57176         Et0/2      point2point

Label 3003 that allocated by P-1,  is the transport label to go to the PE-2 loopback IP Address.

PE-1#sh mpls forwarding-table | i (3003|Outgoing)
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
2002       3003       19.19.19.19/32   0             Et0/0.23   20.2.3.3

In the P-1 router, the transport label 3003 will be swapped to the label 6004 to go the PE-2 loopback IP address.

P-1#sh mpls forwarding-table labels 3003
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
3003       6004       19.19.19.19/32   228000        Et0/0.36   20.3.6.6

And in the P-2 router, the transport label 6004 will be detached and forwarded to the PE-2 router.

P-2#sh mpls forwarding-table labels 6004
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel
Id     Switched      interface

6004       Pop Label  19.19.19.19/32   851677        Et0/0.619  20.6.19.19

Now we verify the AToM pseudowire on the PE-2.

PE-2#show mpls l2transport vc 14 detail | i (up|LDP|label)
Local interface: Se2/0 up, line protocol up, FR DLCI 100 up
  Destination address: 2.2.2.2, VC ID: 14, VC status: up
    Output interface: Et0/0.519, imposed label stack {5013 2014}
  Signaling protocol: LDP, peer 2.2.2.2:0 up
    Targeted Hello: 19.19.19.19(LDP Id) -> 2.2.2.2
    Status TLV support (local/remote)   : enabled/supported
      Last local  LDP TLV    status sent: no fault
      Last remote LDP TLV    status rcvd: no fault
    MPLS VC labels: local 19014, remote 2014
    Group ID: local 0, remote 0

The AToM pseudowire has created and the VC status is up too.  Label 19014 is allocated by PE-2 for the pseudowire. Label 5013 is the transport label that allocated by P-2 to go the VC ID 14 egress router (that is PE-1) loopback IP Address.

PE-2#sh mpls forwarding-table labels 19014
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
Label      Label      or Tunnel Id     Switched      interface
19014      No Label   l2ckt(14)        77876         Se2/0      point2point
PE-2#sh mpls forwarding-table | i (Outgoing|5013)
Local      Outgoing   Prefix           Bytes Label   Outgoing   Next Hop
19008      5013       2.2.2.2/32       0             Et0/0.519  20.5.19.5

We see that the AToM pseudowire for both PE routers have been created and the Virtual Circuit status is up.

Verifying the AToM Interworking

CE-1#ping 10.0.0.20  repeat 1
Type escape sequence to abort.
Sending 1, 100-byte ICMP Echos to 10.0.0.20, timeout is 2 seconds:
!
Success rate is 100 percent (1/1), round-trip min/avg/max = 28/28/28 ms
CE-1#

CE-2#debug ip icmp
ICMP packet debugging is on
CE-2#
*Jun  6 04:25:43.491: ICMP: echo reply sent, src 10.0.0.20, dst 10.0.0.1, topology BASE, dscp 0 topoid 0
CE-2#

We see that the icmp echo packet that send from CE-1 was received by CE-2. Then router CE-2 send the ICMP echo reply packet to the CE-1.