Network routers such as a Cisco Network Routers, Juniper or Brocade Network Routers use a highly distributed routing architecture to deliver feature-rich, wire-speed performance in IPv4/v6/MPLS applications.
These platforms enable the delivery of advanced services over a converged IP/MPLS-based infrastructure. The Network routers offer a range of solutions such as:
Point-to-point Layer 2 MPLS VPNs (Virtual Leased Line, VLL)
Multi-point Layer 2 MPLS VPNs (Virtual Private LAN Service, VPLS)
Layer 3 MPLS VPNs (RFC2547bis)
MPLS Traffic Engineering
IP over MPLS
Frequently Asked Questions
What is MPLS?
MPLS stands for Multi-Protocol Label Switching. MPLS is a framework that allows the introduction of label switching to any combination of Layer 3 and Layer 2 protocols. In an MPLS domain, a packet is examined at the ingress point, its headers are parsed, a routing decision is made, and a label is attached to it. The packet is then forwarded to the next router and the label tells the router what to do with the packet. Hence, the switching decision is made based on the label only – not on the Layer 3 headers. The router discards the label and attaches a new label to be used by the next router. The process continues until the packet emerges at the egress point.
How did MPLS evolve?
MPLS evolved from technologies that were primarily developed in the mid-1990s. The concept of using label switching for a Layer 3 connectionless protocol could be traced back to the mid-1980s. At that time, the high speed networking community was faced with the challenge of increasing IP datagram forwarding rates several orders of magnitude, to the rates of OC-3 and OC-12. Routing based on IP headers used to be performed in software, consuming many CPU cycles, and hence, performance was limited by the processing power of the CPU. The technology has advanced greatly since then.
Network researchers investigated the possibility of using label switching as a means of increasing the forwarding performance in an IP network. Label switching was a much simpler function, and could be implemented in hardware, which made it a very promising approach. In the mid-1990s the concept of label switching started drawing attention again, and several technologies were developed based on it, typically in the context of IP and ATM. The most notable developments were:
Toshiba’s Cell Switching Router, 1995
Ipsilon’s IP Switch, 1996
Cisco’s Tag Switching, 1996
IBM’s Aggregate Route-based IP Switching (ARIS), 1996
In 1997, the MPLS working group was formed with the goal of developing a standard approach for label switching.
Since then, the last 15 years, MPLS has become more and more widely used in many businesses worldwide. It’s become the standard technology used to connect multiple locations together securely and reliably regardless of the distance between the locations. MPLS can be implemented from a T1, to bonded T1′s (NxT1′s), to Ds3′s or ethernet. MPLS Ethernet has become more widely used because it is more cost effective than the MPLS Ds3 circuits. Whenever the solution is available, businesses typically will prefer the ethernet solution vs an MPLS DS3 solution if they need more than 10 mbps.
What benefits does MPLS bring to my network?
Originally, the main benefit of label switching was facilitating high-speed switching in Layer 3 devices. However, this is no longer perceived as the main benefit of MPLS, since ASIC-based routers, nowadays, can perform line-speed routing on most interfaces. Today, the main benefits of MPLS are:
Simplifying packet forwarding: Since the routing decision is made only once at the edge of the network, the core could keep only minimal routing information, thus reducing the overall complexity of the network (e.g. BGP could be run at the edge only, but there would be no need for it in the core).
Traffic Engineering: MPLS connection offers the tools to control the paths taken by different flows. Using these tools, traffic could be rerouted to avoid congestion points in an mpls network.
Delivering Quality of Service (QoS) and Differentiated Services: Using MPLS’ inherent mechanisms for traffic prioritization and traffic path control, a service provider like AT&T or Sprint (or a specialized provider like Masergy) could create a network that delivers QoS, facilitates offering differentiated services to customers, and fulfills the offered service level agreements.
Network scalability: Using MPLS’ label stacking capability, MPLS domains could be arranged in a hierarchy, offering multiple levels of abstraction, and therefore, scalability.
Supporting VPNs: Since MPLS service provides tunneling of packets from an ingress point to an egress point, VPN applications that leverage this capability can be created easily.
Who is responsible for creating the MPLS standards?
The IETF has a specialized working group, the MPLS working group, which is categorized as a sub-IP group. The group is responsible for the development of standards that define the core technology. Other IETF working groups, like the Provider Provisioned Virtual Private Networks working group, might develop standards that make use of the MPLS technology.
Is MPLS meant to replace the current routing protocols?
No. MPLS is not a routing protocol. As a matter of fact, MPLS needs the reachability information provided by the current routing protocols in order to calculate the paths that it uses. MPLS augments the functionality of the routing protocols, but does not replace them.
What is GMPLS?
GMPLS stands for “Generalized MPLS.” GMPLS extends the scope of MPLS to include non-packet based devices that realize the actual Layer 1 paths used, e.g. TDM multiplexers, SONET ADMs, optical (lambda) switches, spatial switches (incoming port to outgoing port), etc.
Is MPLS a protocol?
No. MPLS is a framework of functions, not a protocol. The framework incorporates concepts, mechanisms, and protocols to achieve functions that enhance the current Layer 3 and Layer 2 technologies.
Where does MPLS fit in the OSI reference model?
Some might argue that MPLS does not fit in the OSI reference model. The fact that MPLS is a framework that contains enhancements to the current Layer 3 and Layer 2 technologies makes it hard to fit MPLS within one layer of the OSI model. MPLS alone cannot be considered a layer in the OSI sense as it doesn’t have a unified format for the transport of data from the layer above: it uses a shim header over SONET or Ethernet, it uses the existing VPI/VCI of ATM, etc. However, an individual MPLS function could be categorized as either an OSI Layer 3 or Layer 2 function.
Does MPLS support other protocols other than IP?
Yes. MPLS, by design, was meant to support many Layer 3 and Layer 2 protocols. At Layer 3, MPLS supports IPv4, IPv6, IPX, and AppleTalk. At Layer 2, MPLS supports Ethernet, PPP (for point to point links), Token Ring, FDDI, ATM, and Frame Relay. MPLS was designed to be flexible so that it could work with virtually any Layer 3 and Layer 2 technologies.
How does MPLS compare to ATM?
MPLS brings the label switching and traffic engineering functions of ATM to packet-based networks. MPLS, unlike ATM, runs over any Layer 2 infrastructure, i.e., it is not tied to a certain technology, which allows its use in a heterogeneous environment.
What is the relation between MPLS and VPN’s?
Since MPLS provides tunneling of packets from an ingress point to an egress point, it is an attractive technology for VPN applications. Several types of VPNs – defined in IETF drafts and RFCs – can be implemented over MPLS. These VPNs can be broadly categorized as either MPLS Layer 3 VPNs, or MPLS Layer 2 VPNs.
What does VLL mean?
VLL stands for “Virtual Leased Line”. VLL is a form of MPLS Layer 2 VPN offered as a service by a service provider. The service connects two Customer Edge (CE) devices at two different locations, as if they had a traditional leased line in between. That is, whatever Layer 2 frames the CE device on one end sends are transparently transported to the CE device at the other end of the VLL.
What does TLS mean?
TLS stands for Transparent LAN Services. A service provider offering Layer 2 connectivity to multiple customer sites in a manner that is transparent to the Customer Edge (CE) devices is said to be offering Transparent LAN Services (TLS). The provider takes care of transporting customer Layer 2 frames and switching them across the provider network from one customer site to the other(s). MPLS Layer 2 VPNs could be used to implement these services. In the context of MPLS and provider provisioned IP based VPNs, the preferred term for this service is “VPLS”, which is mentioned in RFC 2764 – “A Framework for IP Based Virtual Private Networks”.
What does VPLS mean?
VPLS stands for “Virtual Private LAN Segment”. A service provider offering Layer 2 connectivity to multiple customer sites in a manner that is transparent to the Customer Edge (CE) devices is said to be offering a Virtual Private LAN Segment (VPLS). This is a new term that was chosen because the service resembles connecting the CE devices via a switch, i.e., all in the same broadcast domain/LAN segment. The provider takes care of transporting customer Layer 2 frames and switching them across the provider network from one customer site to the other(s). MPLS Layer 2 VPNs could be used to implement this service. In the context of classical Layer 2 service provider networks, or ATM networks, the term TLS is used. In the context of MPLS and provider provisioned IP based VPNs, the terms TLS and VPLS are often used interchangeably; however, the preferred term for this service is “VPLS,” which is mentioned in RFC 2764 – “A Framework for IP Based Virtual Private Networks”.
Are there any networks currently utilizing MPLS?
Many service providers have announced that they are using MPLS in their networks. Names include: AT&T, Verizon, Sprint, Centurylink, British Telecom, Cable and Wireless, China Unicom, Deutsche Telekom, France Telecom, Global Crossing/Level 3 Communications, Infonet, Japan Telecom, NTT, Teleglobe, and Time Warner Telecom.
Are there any organizations that perform MPLS interoperability testing?
The Advanced Internet Lab at George Mason University provides interoperability testing services. The lab is sponsored by several equipment manufacturers – including Cisco, Brocade, and Juniper – as well as service providers.
Also, the InterOperability Lab MPLS Consortium at the University of New Hampshire provides these services. Members include Brocade, Cisco, Avici, and others.
This article was written with the information provided by Cisco, Juniper Networks and Brocade Networks as well as the mpls service providers like AT&T, Verizon, Sprint, CenturyLink, Level3, etc.
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