Multiprotocol Label Switching

As explained in Acing the CCNA Exam: Volume 2 Advanced Networking and Security

Multiprotocol Label Switching is a networking technology that forwards packets using labels carried in an additional header rather than relying solely on IP addresses.

Multiprotocol Label Switching (MPLS) connects enterprise LANs across a service-provider WAN, allowing offices to reach systems hosted at remote sites such as a data center. section 16.1

MPLS forwards packets using a fixed-length label rather than relying solely on destination IP addresses. A provider-edge router inserts the additional header between the Layer 2 and Layer 3 headers; routers then forward traffic along a predetermined path. Because the label can carry different packet types, MPLS is often called a Layer 2.5 protocol, although modern deployments usually carry IPv4 or IPv6. section 16.1.2

Identify the router roles in an MPLS WAN:

• Customer edge (CE) routers sit at customer premises and connect the customer network to the provider network; customers typically control them. section 16.1.2
• Provider edge (PE) routers connect customer networks to the provider network and assign or remove MPLS labels. section 16.1.2
• Provider (P) routers operate inside the provider network and forward labeled packets without directly connecting to customer networks. section 16.4

Unlike a leased line, which provides a dedicated connection between two sites, MPLS uses shared provider infrastructure for multiple customers. Labels support traffic segregation through virtual private networks, including Layer 2 VPNs, where the provider network is transparent to CE routers, and Layer 3 VPNs, where CE routers form dynamic-routing relationships with PE routers. section 16.1.2 section 16.4

Figure 16.1 An enterprise WAN connecting four offices and a data center via a service provider’s network infrastructure

Use the WAN topology to identify enterprise sites, the data center, and the provider network boundary. section 16.1

Figure 16.3 The MPLS label is inserted between the Layer 2 and Layer 3 headers.

Inspect the label position between the Layer 2 and Layer 3 headers. section 16.1.2

Figure 16.4 Two customers connect their remote sites via a service provider’s MPLS infrastructure.

Compare multiple customers sharing one provider MPLS infrastructure. section 16.1.2

Figure 16.5 Two customers connect their remote sites using a service provider’s MPLS L2VPN service. PE and P routers are not shown.

Visualize an MPLS Layer 2 VPN between customer sites. section 16.1.2

Figure 16.6 Two customers connect their remote sites using a service provider’s MPLS L3VPN service. CE routers form dynamic routing protocol neighbor relationships with PE routers.

Visualize an MPLS Layer 3 VPN and CE-to-PE dynamic-routing relationships. section 16.1.2

How Acing the CCNA Exam: Volume 2 Advanced Networking and Security covers it

How deep it goes

Defines labels, header placement, forwarding roles, and VPN distinctions while deferring provider-network internals.

Examples

Uses offices, a data center, shared customer networks, label placement, and L2VPN and L3VPN topologies.

What it assumes

Assumes basic LAN, WAN, router, and IP-forwarding knowledge while defining MPLS terminology and roles explicitly.

What you can do after

Evaluate MPLS WAN designs by identifying forwarding behavior, router roles, shared infrastructure, and VPN type.

How it connects

Contrasts MPLS with leased lines and connects it to WANs, Layer 2 VPNs, Layer 3 VPNs, and virtual private networks.

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Related concepts

• MPLS L3VPNused by · An MPLS L3VPN is a Layer 3 virtual private network in which provider edge routers participate in customer routing and maintain separated routing information.
• MPLS L2VPNused by · An MPLS L2VPN is a Layer 2 virtual private network in which the provider network transparently forwards customer frames between customer edge routers.
• MPLS labeluses · An MPLS label is a fixed-length header value inserted into a packet to identify a predetermined forwarding path through an MPLS network.
• wide area networkused by · A wide area network is a computer network that connects devices or smaller networks across a broad geographical area.
• virtual private networkproduces · A virtual private network is a logical network that connects systems across an underlying network through protected, typically encrypted, communication.
• leased linealternative to · A leased line is a dedicated telecommunications connection rented from a provider for continuous private use between specified locations.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 2 Advanced Networking and Security. The section links point to the parts of the book it draws on.