Multiprotocol Packet Label Switching (MPLS) uses a fixed-path approach to routing packets across a network. The first router to encounter a packet attaches a label to the packet that corresponds to a fixed path to the final destination. Other routers along the way then simply read the label on the packet and use that label to determine where the packet should go next, without performing any lookups. Learn how MPLS networks function.
- [Instructor] MPLS provides an efficient way to route traffic along fixed network paths. The vast majority of networks use IP address based routing to send packets on their way. By looking at the destination IP address and comparing it to internal routing tables at each hop along the way seeking the best possible route to the final destination. This approach can be time consuming for the routers involved. At each step, the router must verify the final destination IP address.
Look that address up in routing tables and attempt to determine the best path to the final destination. Packets between point A and point B may wind up taking very different paths through the network. Multiprotocol Packet Label Switching, MPLS, uses a fixed path approach to routing packets across a network. The first MPLS router to encounter a packet attaches a label to the packet that corresponds to a fixed path to the final destination.
Other routers along the way then simply read the label on the packet and use that label to determine where the packet should go next, without performing any look ups. Every step along the way is pre-determined by the first router. MPLS is an interesting protocol. It doesn't fit cleanly in to the OSI Model because it performs functions that belong to both the Data Link and Network Layers. It basically fits right here, in the middle. For that reason, many people refer to MPLS as a layer 2.5 protocol.
You can think of MPLS networks as a tunnel where the first router is the entry point to the tunnel and the last router is the exit point. The first router is known as the Label Edge Router or LER. The LER is responsible for analyzing each packet and determining the best path through the network to the final destination. The LER then places the packet in to the tunnel for delivery. The tunnel is also known as the Label Switched Path or LSP.
And the final destination router is known as the Egress Node. The Egress Node is the other end of the MPLS tunnel. It has the responsibility of removing the label from the packet and then delivering that packet using standard mechanisms. Which usually means IP based networking. The MPLS tunnel between the LER and the Egress Node is actually comprised of one or more routers that are selected by the LER when it attaches the label. Each of these intermediate routers is known as a Label Switching Router or LSR.
These LSR's don't need to know very much. They simply look at the label on the packet and then from looking at that label they know where to send the packet as the next step in that fixed route. So how do all the nodes in the label switched path know where to send each packet they receive? MPLS Routing Protocols make this happen. There are two MPLS Routing Protocols. The Label Distribution Protocol, LDP is the simplest of the two. LDP simply tells all of the routers in the label switched path the label, chosen by label edge routers and the label switched router's role in carrying out that path.
The second MPLS Routing Protocol is the Reservation Resource Protocol with Traffic Engineering or RSVP-TE. This protocol also performs the same function as LDP but it adds traffic engineering capabilities that allow network engineers to reserve bandwidth for a label switched path to provide quality of service assurances.
Learn about communication and networking best practices, including TCP/IP networking, network security devices, and secure network design and management. Instructor and cybersecurity expert Mike Chapple also includes coverage of converged protocols, network encryption, and wireless networking. You can find Mike's companion study books for this series at the Sybex test prep site and review the complete CISSP Body of Knowledge at https://www.isc2.org/cissp-domains/default.aspx.
- IP addressing
- Switches and routers
- Content distribution networks
- Designing secure networks
- Specialized networking
- Managing secure networks
- Working with virtualized networks like SDNs
- Detecting and preventing network attaches
- Transport encryption
- Wireless networking
- Host security