Basic knowledge about MPLS protocol stack structure

The advantages of Multi-Protocol Label Switching MPLS are described here. This article mainly introduces the MPLS protocol stack structure. First, let's start with the concept of multi-protocol labels, and then explain its label structure and protocol stack structure.

Multi-Protocol Label Switching (MPLS) is a system for Fast Packet Exchange and routing. It provides the target, route, forwarding, and exchange capabilities for network data traffic. What's more, it has a mechanism to manage various forms of communication streams. MPLS is independent of Layer 2 and Layer 3 protocols, such as ATM and IP. It provides a way to map IP addresses to simple labels with fixed lengths for different packet forwarding and packet switching technologies. It is an interface for existing routing and switching protocols, such as IP, ATM, frame relay, Resource Reservation Protocol (RSVP), and Open Shortest Path (OSRF.

In MPLS, data transmission occurs on the label switching path LSP. LSP is the label sequence of each node along the path from the source end to the terminal. Currently, some label distribution protocols, such as the Label Distribution Protocol LDP), RSVP, or some protocols built on the routing protocol, such as Border Gateway Protocol BGP) and OSPF are used. Because a fixed-length label is inserted at the beginning of each package or cell and can be used by hardware to quickly exchange packets between two links, fast data exchange is possible.

MPLS is designed to solve network problems, such as network speed, scalability, service quality QoS) Management and traffic engineering. It also solves problems such as broadband management and service requests for the Next Generation IP hub network.

In this section, we focus on the general MPLS framework. For details about LDP, CR-LDP, and RSVP-TE, refer to individual files.

MPLS protocol stack structure

MPLS label structure:

20	23	24	32 bit
Label	Exp	S	TTL

Label-transfer the actual value of the Label. When receiving A tag packet, you can find the tag value at the top of the stack, and the system knows that A, the next hop of the packet will be forwarded; b. operations that may be performed on the tag stack before forwarding. For example, a tag can be pushed out of the stack at the top of the stack; or return the tag to the top of the stack and push one or more tags to the stack.

Exp-trial. Reserved for trial use.

S-stack bottom. The position of the last incoming tag in the tag stack. The value is 0, and all other tags are provided into the stack.

TTL-Time to Live), used to encode the Time to Live value.

MPLS structure protocol groups include:

MPLS: Related Signaling Protocols, such as OSPF, BGP, and atm pnni.

LDP: Label Distribution Protocol)

CR-LDP: Based on routing restricted Label Distribution Protocol Constraint-Based LDP)

RSVP-TE: resource Reservation Protocol-Traffic Engineering Based on Traffic Engineering extension)

The following figure describes the MPLS protocol stack structure:

;

MPLS protocol stack structure