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MPLS brings new functionality to IP

MPLS allows for the creation of low cost VPNs, but some say this is at the price of security.

MPLS is a technology that promises to bring QoS (Quality of Service) to IP networks as well as allowing network engineers to fine tune traffic strategies. This protocol also allows for the creation of low cost VPNs, but some say this is at the price of security.

Multi-Protocol Label Switching (MPLS), a technology that allows network architects to handcraft traffic patterns to meet their specific needs, is expected to be readily adopted by users as networks carry increasing volumes of mixed traffic. As a result, MPLS will have a big impact on enterprise networks.

According to Irwin Lazar, senior consultant at Midvale, Utah-based Burton group, MPLS performs a variety of tasks. Some of the most important include serving as a mechanism for tunneling traffic in IP networks, bringing connection oriented properties to connectionless networks, and predefining network traffic flow.

"Other benefits of MPLS are lower cost VPNs, interoperability between sites, and quality of service guarantees for the IP layer," Lazar said.

MPLS works by assigning each incoming packet a label. Label edge routers assign labels and use label switch paths to send the packets. Label switch paths can be customized to meet the needs of the network. Each time a packet makes a hop to another router it gets a new label and can be sent along to its destination. Packet forwarding is based entirely on the contents of the label. MPLS technology also allows for traffic classification and prioritization by using Forward Equivalence Classes (FEC). A Forward Equivalence Class is a description of the criteria used to determine if a set of packets is to be forwarded in an equivalent fashion along the same label switch path.

MPLS also extends the capability of existing IP networks, which makes it an appealing option for many users seeking to save time and money on permanent virtual circuits and traditional VPNs, according to Lazar. The technology also allows the conjunction of IP to layer two technologies such as ATM and Frame Relay, by overlaying a protocol on top of IP networks.


"Using MPLS allows enterprises an integrated, simplified way of connecting sites. It eliminates Permanent Virtual Circuits and lets the service provider do the dirty work," said Lazar.

Most enterprises today don't take on MPLS implementation by themselves. When it comes to implementing MPLS it's best to stick with a service provider. One reason is that configuration of label switch paths (LSPs), the MPLS equivalent to PVCs, requires specialized expertise. Hardware configuration is another reason that MPLS implementation should be left to the pros, said Lazar. MPLS requires high-end network routers to take full advantage of the technology. The bottom line is, unless your enterprise is ready to commit the time, money, and effort for training, testing, and truckloads of new hardware, get a service provider.

Kevin Mitchell, directing analyst for service provider networks at San Jose, Calif.-based Infonetics Research said MPLS allows service providers to offer their customers more network option packages and better performance. "It [an MPLS network] should be transparent to the enterprise, except for better SLAs from the carrier, because of traffic engineering," said Mitchell. In other words, an MPLS network shouldn't feel any different to a user at their desk than a Frame Relay or ATM Network. "It should also allow them [service providers] to offer more flexible packages," said Mitchell.

Obstacles and concerns

Multi-vendor networks can pose obstacles to MPLS implementations. This is because MPLS requires high-end routers that must be specifically configured for the protocol. The degree of difficulty increases with the variety of vendor hardware on the network.

"Vendor integration can be a pitfall to MPLS implementation. The more advanced features may be harder to implement on mixed vendor networks. It's much easier to do on an all Cisco or an all Marconi or other single vendor network," said Lazar.

Security is also a concern for networks implementing MPLS VPNs because the technology has no native encryption capabilities.

"MPLS VPNs are not for everyone. If you want security, you are going to need something for encryption," said Mitchell.

According to Mitchell the technology also lacks a proven track record for the enterprise. "MPLS isn't proven for working on a large scale, it also lacks a justifiable business case," Mitchell said.

The standards for MPLS are still maturing as well. Most MPLS standards are currently in the Internet draft phase, though several have now moved into the (Request For Comments Standard) RFC-STD phase. This means that a basic standard is defined, but may be superceded or elaborated on by changes made to subsequent or previous RFCs.

"The base functional RFC is stable, and there is a ton of effort going into defining extensions so that the more advanced functions of MPLS will become standardized," said Lazar.

Despite the developing standard, lack of native encryption, and the difficulty of installation on heterogeneous networks, MPLS can be an attractive way for enterprises to handle diverse network traffic, build cost effective VPNs, and bring quality of service to existing IP networks.


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This was last published in April 2002

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