MPLS and VPN Terms

color

See link coloring.

Constrained Shortest Path First (CSPF)

MPLS algorithm that has been modified to include specific restrictions for calculating the shortest path across the network.

customer edge (CE) router

Services Router or switch in the customer's network that is connected to a service provider's provider edge (PE) router and participates in a Layer 3 VPN.

Explicit Route Object (ERO)

Extension to the Resource Reservation Protocol (RSVP) that allows an RSVP PATH message to traverse an explicit sequence of routers independently of conventional shortest-path IP routing.

inbound router

Entry point for a label-switched path (LSP). Each LSP must have exactly one inbound router that is different from the outbound router. Inbound routers are also known as ingress routers. See also outbound router.

label

In Multiprotocol Label Switching (MPLS), a 20-bit unsigned integer in the range 0 through 1,048,575, used to identify a packet traveling along a label-switched path (LSP).

Label Distribution Protocol (LDP)

Protocol for distributing labels in non-traffic-engineered applications. LDP allows Services Routers to establish label-switched paths (LSPs) through a network by mapping Network layer routing information directly to Data Link Layer switched paths.

label-switched path (LSP)

Sequence of Services Routers that cooperatively perform Multiprotocol Label Switching (MPLS) operations for a packet stream. The first router in an LSP is called the inbound router, and the last router in the path is called the outbound router. An LSP is a point-to-point, half-duplex connection from the inbound router to the outbound router. (The inbound and outbound routers cannot be the same router.)

label-switching router (LSR)

Any Services Router that is part of an LSP.

Layer 2 circuit

Point-to-point Layer 2 connection transported by means of Multiprotocol Label Switching (MPLS) or another tunneling technology on a service provider’s network. Multiple Layer 2 circuits can be transported over a single label-switched path (LSP) tunnel between two provider edge (PE) routers.

Layer 2 VPN

Private network service among a set of customer sites that use a service provider's existing Multiprotocol Label Switching (MPLS) and IP network. One customer's data is separated from another's by software rather than hardware. In a Layer 2 VPN, the Layer 3 routing of customer traffic occurs within the customer network.

Layer 3 VPN

Private network service among a set of customer sites that use a service provider's existing Multiprotocol Label Switching (MPLS) and IP network. One customer's routes and data are separated from another customer's routes and data by software rather than hardware. In a Layer 3 VPN, the Layer 3 routing of customer traffic occurs within the service provider network.

link coloring

In Constrained Shortest Path First (CSPF) routing, a way to group Multiprotocol Label Switching (MPLS) interfaces for CSPF path selection by assigning a color identifier and number to each administrative group.

Multiprotocol Label Switching (MPLS)

Method for engineering network traffic patterns by assigning short labels to network packets that describe how to forward the packets through the network.

multiple push

Addition by a Services Router of up to three labels to a packet as it enters a Multiprotocol Label Switching (MPLS) domain.

outbound router

Exit point for a label-switched path (LSP). Each LSP must have exactly one outbound router that is different from the inbound router. Outbound routers are also called egress routers. See also inbound router.

penultimate hop popping (PHP)

Using the penultimate router rather than the outbound router in a label-switched path (LSP) to remove the Multiprotocol Label Switching (MPLS) label from a packet.

penultimate router

Second-to-last Services Router in an LSP. The penultimate router is responsible for label popping when penultimate hop popping (PHP) is configured.

point-to-multipoint LSP

Label-switched path (LSP) that allows a network operator to use MPLS for point-to-multipoint data distribution in an efficient manner. Point-to-multipoint LSPs add IP multicast functionality to MPLS.

pop

Removal by a Services Router of the top label from a packet as it exits the Multiprotocol Label Switching (MPLS) domain.

provider edge (PE) router

Services Router in the service provider network that is connected to a customer edge (CE) router and participates in a virtual private network (VPN).

provider router

Services Router in the service provider’s network that does not attach to a customer edge (CE) router.

push

Addition of a label or stack of labels by a Services Router to a packet as it enters a Multiprotocol Label Switching (MPLS) domain.

Resource Reservation Protocol (RSVP)

Resource reservation setup protocol that interacts with integrated services on the Internet.

route distinguisher

A 6-byte virtual private network (VPN) identifier that is prefixed to an IPv4 address to make it unique. The new address is part of the VPN-IPv4 address family, which is a Border Gateway Protocol (BGP) extension. A route distinguisher allows you to configure private addresses within the VPN by preventing any overlap with the private addresses in other VPNs.

routing instance

Collection of routing tables, their interfaces, and the routing protocol parameters that control the information they contain.

swap

Replacement by a Services Router of a label or stack of labels on a packet as it travels through a Multiprotocol Label Switching (MPLS) domain.

swap and push

Replacement and subsequent push by a Services Router of a label or stack of labels on a packet as it travels through a Multiprotocol Label Switching (MPLS) domain.

Traffic engineering (TE)

The techniques and processes used to cause routed traffic to travel through the network on a path other than the one that would have been chosen if standard routing methods had been used.

traffic engineering database (TED)

Database populated by label-switched path (LSP) information such as the network topology, current reservable bandwidth of links, and link colors. The traffic engineering database is used to determine Constrained Shortest Path First (CSPF) path selection.

transit router

Any label-switching router (LSR) between the inbound and outbound Services Router of a label-switched path (LSP).

virtual private network (VPN)

Private data network that uses a public TCP/IP network, typically the Internet, while maintaining privacy with a tunneling protocol, encryption, and security procedures.

VPN routing and forwarding (VRF) instance

Routing instance for a Layer 3 VPN implementation that consists of one or more routing tables, a derived forwarding table, the interfaces that use the forwarding table, and the policies and routing protocols that determine what goes into the forwarding table.