Multiprotocol Label Switching - What Is It and Why It Rocks!

Multiprotocol Label Switching (MPLS) is an approach to routing data through a network, primarily by relying on labels affixed to packets, rather than by inspecting packets' contents, except at the network's edges.

When packets enter an MPLS network, any packets that are not immediately discarded have one or more labels added to them. As these labelled packets pass through the MPLS network, 'label switch routers' within the network examine the outer-most label. These routers can add, swap or remove labels.

Finally, when a packet reaches the final or penultimate router on its journey through the network, all remaining MPLS labels are stripped off. From then on, the packet is routed based on other factors, such as the destination IP address (for Internet traffic) or MAC address (for Ethernet frames).

Why bother with Multi-Protocol Label Switching?

Good question. At first glance, MPLS may appear a bit pointless. Why add labels only to remove them later? Why mess around with those labels, pushing, popping and swapping them?

The answer is that Multi-Protocol Label Switching's apparent simplicity can be used to create complex desirable outcomes.

For example, let's imagine an MPLS provider wants to join 20 office LANs together to form a corporate WAN for one of its customers. To do that, it may choose to use circuits from five different underlying carriers, in conjunction with circuits from its own core network. MPLS lets the provider hide the underlying complexity from its client. The client just sees a single network on which they can prioritise traffic as they wish.

An MPLS network provider could also use MPLS to help create a virtual private LAN service, linking two locations in such a way that it will appear as though there's just a long ethernet cable linking the two sites - with no network-address-translation, IP addressing or carrier hubs visible. As far as their customer knows, getting data from A to B is just a single hop.

MPLS also has a feature called Fast Reroute that makes it possible to switch traffic to an alternative path extremely rapidly. If the primary path ceases to be a feasible option, traffic can be diverted down an alternative path, minimising the disruption caused by physical circuit faults.

The layer of abstraction provided by the labels also makes troubleshooting easier.

Why Multiprotocol Label Switching Rocks

MPLS is a lot like duct tape. Deceptively simple, but surprisingly flexible in the ways it can be used.

For example, the layer of abstraction provided by labels allows MPLS networks to carry both layer 2 and layer 3 traffic over the same connections. 

If set up correctly, MPLS networks can support increased link utilisation, without noticeably harming the customer experience. They are able to re-route delay-tolerant traffic (if it's suitably labelled so as to be identifiable) to slower less congested routes if required.

Class of Service options can be used to help prioritise traffic on congested links so that the impact of network congestion on user experience is minimised.

Upgrading network connections costs money. Network operators don't want to spend that money until the upgrade is close to being necessary. Any technology - including MPLS - that enables an existing network to be used more fully, postponing expensive upgrades, will prove popular.

Large-scale network operators such as ISPs and telecoms carriers that currently rely on MPLS are likely to continue to do so. However, they may stop mentioning, given the anti-MPLS messages being promoted by SD-WAN equipment vendors.

Software-Defined WANs - Displacing Multiprotocol Label Switching in Some Corporate WANs

MPLS is used primarily for multi-site networks, such as ISPs' networks, carrier networks and corporate WANs.

When it comes to corporate WANs, MPLS now has a rival of sorts in Software-Defined Wide Area Network (SD-WAN) technologies. SD-WANs can achieve some of the traffic prioritisation, connection bonding and connection failover functions that MPLS can perform. In addition, SD-WANs can use deep packet inspection to help integrate more nuance into traffic management.

SDWANs aren't without their downsides. SDWAN hardware isn't cheap, particularly if you have a lot of sites to connect. SDWANs arguably duplicate some of the functions that existing firewalls may be able to provide. Furthermore, much SD-WAN technology isn't designed for use on high-capacity multi-gigabit links.

Here at hSo, we can provide UK businesses with MPLS WANs and SD-WANs. To check which is right for your particular situation, call us on 020 7847 4510.