# Configuring HDLC Layer 2 Services

The following commands configure an HDLC layer 2 circuit over MPLS between an E Series router and a remote PE device.

To configure an HDLC layer 2 circuit over MPLS:

1. Configure a serial or POS interface on the ingress router.
   host1(config)#interface serial 3/1:2/1

   or

   host1(config)#interface pos 4/0
2. Use one of the following methods to create the HDLC layer 2 circuit over MPLS:
   - Use the mpls-relay or route interface command without the relay-format ppp keywords. This command causes the router to signal VC-type HDLC on the LDP session and use HDLC encapsulation. Use this command syntax if the traffic carried on the serial or POS interface is any kind of standard HDLC (including PPP) or Cisco HDLC.
     host1(config-if)#mpls-relay 2.2.2.1 1

     or

     host1(config-if)#route interface tunnel mpls:tunnel-to-pe2 1
   - Use the mpls-relay or route interface command with the relay-format ppp keywords. This command causes the router to signal VC-type PPP on the LDP session and use PPP encapsulation instead of the default VC-type HDLC signaling and HDLC encapsulation. Use this command syntax if the traffic carried on the serial or POS interface contains actual PPP packets.
     host1(config-if)#mpls-relay 2.2.2.1 1 relay-format ppp

     or

     host1(config-if)#route interface tunnel mpls:tunnel-to-pe2 1 relay-format ppp
3. (Optional) Attach an MPLS policy to the HDLC layer 2 circuit by using the mpls policy command.
   host1(config-if)#mpls policy input hdlc-policy
4. Configure the serial or POS interface and MPLS on the remote PE device.

   The interfaces at either end of the HDLC layer 2 circuit can be different types and have different speeds. For example, you can configure an HDLC layer 2 circuit between a serial interface on a T1 circuit and a POS interface on an OC3 circuit.

- Local Cross-Connects for HDLC Layer 2 Services Configuration Differences

## Local Cross-Connects for HDLC Layer 2 Services Configuration Differences

You can also configure an HDLC layer 2 circuit in a local cross-connect configuration between serial or POS interfaces within the same router.

The procedure is basically the same for configuring an HDLC layer 2 interface between two PE routers and for a local cross-connect, with the following differences for local cross-connects:

- You must use the mpls-relay command instead of the route interface command to configure a local cross-connect for HDLC layer 2 services.
- You use the IP address of the local router as the value for the destination IP address (remote address) in the mpls-relay command.