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Understanding MPLS Components

Provider Edge Switches

To implement MPLS on a network, you must configure two provider edge (PE) switches—that is, an ingress PE switch and an egress PE switch. In addition, you must configure one or more provider switches as transit switches within the network to support the forwarding of MPLS packets.

The ingress PE switch (the entry point to the MPLS tunnel) receives a packet, analyzes it, and pushes an MPLS label onto it. This label places the packet in a forwarding equivalence class (FEC) and determines its handling and destination through the MPLS tunnel. The egress PE switch (the exit point from the MPLS tunnel) pops the MPLS label off the outgoing packet.

Within an MPLS tunnel, the network traffic is bidirectional. Therefore, each PE switch can be configured to be both an ingress switch and an egress switch, depending on the direction of the traffic.

The following MPLS components are configured on the PE switches but not on the provider switches:

• MPLS Protocol and Label-Switched Paths
• IP Over MPLS for Customer Edge Interfaces
• BGP Layer 3 VPN Configuration
• Routing Instances for Layer 3 VPN

MPLS Protocol and Label-Switched Paths

Each PE switch must be configured to support the MPLS protocol. You must also configure label-switched paths (LSPs) at the [edit protocols mpls] hierarchy level.

IP Over MPLS for Customer Edge Interfaces

You can configure the customer edge interfaces of the PE switches for IP over MPLS using a Layer 3 interface and a static route from the ingress PE switch to the egress PE switch. See Configuring MPLS on Provider Edge Switches.

BGP Layer 3 VPN Configuration

If you are implementing a Layer 3 virtual private network (VPN), you must configure the BGP routing protocol on the PE switches.

Routing Instances for Layer 3 VPN

If you are implementing a Layer 3 VPN, you must configure a routing instance. A routing instance is a collection of routing tables, interfaces, and routing protocol parameters. The set of interfaces belongs to the routing tables, and the routing protocol parameters control the information in the routing tables.

QFX Series devices and EX4600 support VPN routing and forwarding (VRF) routing instances for Layer 3 VPNs.

Each routing instance has a unique name and a corresponding IP unicast table. For example, if you configure a routing instance with the name my-instance, its corresponding IP unicast table will be my-instance.inet.0. All routes for my-instance are installed in my-instance.inet.0.

Provider Switch

You must configure one or more provider switches as transit switches within the network to support the forwarding of MPLS packets. You can add provider switches without changing the configuration of the PE switches.

A provider switch does not analyze packets. It refers to an MPLS label forwarding table and swaps one label for another. The new label determines the next hop along the MPLS tunnel. A provider switch cannot perform push or pop operations.

Components Required for All Switches in the MPLS Network

The following MPLS components are configured on both the PE switches and the provider switches:

• Interior Gateway Protocol
• MPLS Protocol
• RSVP
• Family mpls

Interior Gateway Protocol

MPLS works in coordination with OSPF as the interior gateway protocol (IGP). Therefore, you must configure OSPF as the IGP on the loopback interface and core interfaces of both the PE switches and the provider switches.

The core interfaces can be either Gigabit Ethernet or 10-Gigabit Ethernet interfaces, and they can be configured as either individual interfaces or as aggregated Ethernet interfaces.

Note: The core interfaces cannot be configured with VLAN tagging or a VLAN ID. When you configure them to belong to family mpls, they are removed from the default VLAN if they were members of that VLAN. They operate as an exclusive tunnel for MPLS traffic.

MPLS Protocol

You must enable the MPLS protocol on all switches that participate in the MPLS network and apply it to the core interfaces of both the PE and provider switches. You do not need to apply it to the loopback interface because the MPLS protocol uses the framework established by the RSVP signaling protocol to create LSPs. On the PE switches, the configuration of the MPLS protocol must also include the definition of an LSP.

RSVP

RSVP is a signaling protocol that allocates and distributes labels throughout an MPLS network. RSVP sets up unidirectional paths between the ingress PE switch and the egress PE switch. RSVP makes the LSPs dynamic; it can detect topology changes and outages and establish new LSPs to allow traffic to move around a failure.

You must enable RSVP and apply it to the loopback interface and the core interface of both the PE and provider switches. The path message contains the configured information about the resources required for the LSP to be established.

When the egress PE switch receives the path message, it sends a reservation message back to the ingress PE switch. This reservation message is passed along from switch to switch along the same path as the original path message. Once the ingress PE switch receives this reservation message, an RSVP path is established.

The established LSP stays active as long as the RSVP session remains active. RSVP continues activity through the transmissions and responses to RSVP path and reservation messages. If the messages stop for three minutes, the RSVP session terminates and the LSP is lost.

RSVP runs as a separate software process in Junos OS and is not in the packet-forwarding path.

Family mpls

You must configure the core interfaces used for MPLS traffic to belong to family mpls.

Note: You can enable family mpls on either individual interfaces or on aggregated Ethernet interfaces. You cannot enable it on tagged VLAN interfaces.