Multiprotocol Label Switching, the forwarding paradigm that powers most service provider backbones and large enterprise WANs. Articles tagged MPLS cover labels and the label stack, LDP, L3VPN with MP-BGP and VPNv4, traffic engineering, and segment routing.
MPLS Traffic Engineering exists to solve a problem the IGP creates. OSPF and IS-IS always forward along the shortest path, every flow, all the time. That is correct for reachability and terrible for capacity: the shortest path saturates while
A fabric that cannot talk to anything outside itself is a very expensive island. The border node is how an SD-Access fabric connects to the rest of the world - the data centre, the WAN, the internet, another fabric - and
Transport technologies fail in layers, and the art of troubleshooting them is knowing which layer to suspect. An MPLS L3VPN has an IGP, LDP, MP-BGP, VRFs, and a label stack, any one of which can break while the others
Almost every mid-to-large enterprise WAN ends up running both MPLS and DMVPN. Not because someone planned it that way, but because they solve different problems, and a real network has both problems. MPLS gives you a private, SLA-
BGP is the most powerful choice for the PE-CE protocol in an MPLS L3VPN - it scales, it carries policy, and it hands the provider fine-grained control. But it comes with a trap that catches every engineer once: BGP&
You have an IPv4 MPLS L3VPN running. Your customers each have their own VRF, their own routing table, their own isolated slice of the core. It works, it scales, it makes money. Then a customer asks for IPv6, and you
Here is a problem that a great many service providers had, and some still have: a fully working, fully tuned, IPv4-only MPLS core, and customers who want IPv6. Upgrading every P router in the core to dual-stack is
An MPLS L3VPN route makes a long journey. It starts as an IP prefix in a customer's routing table, gets learned by a PE into a VRF, redistributed into MP-BGP, tagged with a route target, given a
MPLS forwarding runs on labels, not on IP reachability, so a dead LDP session leaves every green light green while the customer blackholes. Captured on CML with IOS XE 17.18.2: the unusable: no label CEF entry, the full LDP LIB, a hop-by-hop walk to find where the binding stops, and No Label...
Ask ten network engineers to explain the difference between a route distinguisher and a route target and you will get four confident wrong answers, three "they're basically the same thing," and maybe three correct ones. The
Once the MPLS core is built and MP-BGP is carrying VPNv4 between your PEs, one question remains: how does a PE router actually learn the customer's routes? That is the PE-CE routing protocol, and it is
MPLS L3VPN is the service that made MPLS a service-provider standard, and it is still what most enterprises are actually buying when their carrier sells them "an MPLS circuit." The concept is simple to state and surprisingly