Last updated: May 1, 2026
For two decades, “the corporate WAN” meant MPLS — leased L3 VPNs from Tata, Airtel, Sify, Reliance, BSNL connecting branches to headquarters and data centres. MPLS works well; it is also expensive, slow to provision, and rigidly policy-controlled by the carrier. SD-WAN — software-defined WAN — promises the same predictability over cheaper, more flexible transports plus integrated security. This module covers both worlds and the migration path that most Indian enterprises are now actively executing.
MPLS — what it actually is and why carriers like it
Multiprotocol Label Switching (RFC 3031) attaches small “labels” to packets at the carrier edge. Inside the carrier network, switches forward by label rather than IP — fast, simple, with operator-controlled paths. MPLS L3VPN uses VRFs (Module 13) per customer; each customer’s prefixes live in their own routing table, isolated from other customers on the same physical infrastructure. The customer-facing edge router (CE) talks BGP or static routes to the provider edge (PE); inside the carrier, BGP-VPN distributes routes; LDP or RSVP-TE assigns labels.
Why customers liked itpredictable latency and jitter, SLA-backed, the carrier handles reachability — the enterprise just connects branches and lets the carrier worry about paths.
Why it is being replacedcost (10-20× per Mbps versus broadband), provisioning lead times (weeks for new branches), and inflexibility (carrier-controlled, slow to adapt to traffic patterns).
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