Figure 55: Explicit Routing in an MPLS Domain
MPLS Interfaces and Interface Stacking
The JUNOSe implementation of MPLS employs MPLS major, minor, and shim
interfaces.
MPLS Major Interfaces
An MPLS major interface must be stacked on a layer 2 interface to send or receive
MPLS packets on that interface. Each MPLS major interface exists in a particular
virtual router.
MPLS major interfaces can use the platform label space or the interface label space.
Which type of label space is used by the major interface is determined by the layer 2
interface on which the major interface is stacked. If the layer 2 interface is an ATM
AAL5 interface, the major interface uses the interface label space. For all other layer
2 interface types, the major interface uses the platform label space.
When an MPLS packet arrives on the MPLS major interface, MPLS looks up the label
of the received MPLS packet, the in label, in the MPLS forwarding table that is
associated with the major interface. For major interfaces using the platform label
space, the lookup is in the MPLS forwarding table of the VR. For major interfaces
using the interface label space, the lookup is in the MPLS forwarding table of the
major interface.
You use the mpls command in Interface Configuration mode to create or remove
MPLS major interfaces. Some other commands create an MPLS major interface if it
does not already exist.
You can configure the following attributes for each MPLS major interface:
â– The administrative state, enabled or disabled, configured with the mpls disable
command.
â– The range of ATM VPIs used as interface labels for major interfaces stacked on
ATM AAL5 interfaces, configured with the mpls atm vpi range command.
â– The range of ATM VCIs used as interface labels for major interfaces stacked on
ATM AAL5 interfaces, configured with the mpls atm vci range command.
MPLS Interfaces and Interface Stacking â– 227
Chapter 2: MPLS Overview
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