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Constrained Shortest Path First

Constrained Shortest Path First (CSPF) is an extension of shortest path algorithms.

Version
v1 · 2026-09-28 · History
Domain-specific #
8665
Domain group
Applied Sciences & Engineering
Origin domain
Computer Science & Software Engineering
Subdomains
Computer Networking, Traffic Engineering → Computer Science & Software Engineering

Core Idea

Constrained Shortest Path First is treated here as the recurring computer science and information systems identity summarized by this source-grounded definition: Constrained Shortest Path First (CSPF) is an extension of shortest path algorithms. Constrained Shortest Path First (CSPF) is an extension of shortest path algorithms. The path computed using CSPF is a shortest path fulfilling a set of constraints. It simply means that it runs shortest path algorithm after pruning those links that violate a given set of constraints.

How would you explain it like I'm…

Cross Out, Then Go Short

Imagine you want the shortest way to your friend's house, but your wagon is too wide for some narrow paths. So first you cross out every path your wagon can't fit on, then you find the shortest way using only the paths that are left. That's Constrained Shortest Path First.

Shortest Route That Follows Rules

Constrained Shortest Path First is a way for computer networks to pick a route. Normally you would just pick the shortest route. With this method, you first remove any links that break a rule, like a link that can't carry enough data, and then find the shortest route through what remains. Rules can be about how much data a link can carry, how long the trip takes, how many hops it uses, or which spots must be included or avoided.

Constraint-Pruned Shortest Path

Constrained Shortest Path First (CSPF) extends ordinary shortest-path algorithms. It finds the shortest path that also satisfies a set of constraints. The basic method is simple: prune away every link that violates the constraints, then run a normal shortest-path algorithm on the remaining network. Typical constraints are a minimum bandwidth per link, a limit on end-to-end delay, a maximum number of hops, or nodes that must be included or excluded. It is widely used in MPLS traffic engineering, and routing that uses it is called constraint-based routing.

 

Constrained Shortest Path First (CSPF) is an extension of shortest-path computation in which the selected path must satisfy a set of constraints. Operationally, links that violate the constraints are pruned from the topology, and a standard shortest-path algorithm is then run on the pruned graph. Constraints include per-link minimum available bandwidth (the bandwidth-guaranteed constraint), end-to-end delay, a maximum hop count, and explicit include or exclude nodes. CSPF is widely used in MPLS Traffic Engineering to compute label-switched paths, and routing driven by it is called Constraint Based Routing (CBR). The key point is that the result is the shortest path among feasible paths, not simply the shortest path.

Scope of Application

  • Example with bandwidth constraint. For example, suppose that as before, hop count is used as link cost for all links but A → B and B → C, for which the cost is 4.

  • Documented setting. CSPF is widely used in MPLS Traffic Engineering.

  • Example with bandwidth constraint. Consider the network to the right, where a route has to be computed from router-A to the router-C satisfying bandwidth constrained of x- units, and link cost for each link is.

  • Example with bandwidth constraint. If x = 50 units then CSPF will give path A → B → C.

  • Example with bandwidth constraint. If x = 55 units then CSPF will give path A → D → E → C.

Clarity

A clear use of Constrained Shortest Path First names the carrier, the operative relation, and the conditions under which the source treats the identity as present. The minimal definition is Constrained Shortest Path First (CSPF) is an extension of shortest path algorithms. The strongest recognition evidence in the frozen account is: If x = 50 units then CSPF will give path A → B → C.

Manages Complexity

Constrained Shortest Path First compresses multiple computer science and information systems details into a stable diagnostic relation. The source shows both the central mechanism—the path computed using CSPF is a shortest path fulfilling a set of constraints.—and the practical consequence—if x = 90 units then CSPF will give path A → D → E → F → C. This compression makes cases comparable while leaving parameters, conventions, exceptions, and evidential quality explicit.

Abstract Reasoning

  1. Type the carrier. Identify the computer science and information systems entities to which the claim applies.
  2. State the relation. Use the source-grounded identity: Constrained Shortest Path First (CSPF) is an extension of shortest path algorithms.
  3. Check operation and conditions. The path computed using CSPF could be exactly same as that of computed from OSPF and IS-IS, or it could be completely different depending on the set of constraints to be met.
  4. Demand recognition evidence.

Knowledge Transfer

Within the home domain. Knowledge about Constrained Shortest Path First transfers literally when a new case preserves the same carrier type, relation, and recognition test. For example, suppose that as before, hop count is used as link cost for all links but A → B and B → C, for which the cost is 4. CSPF is widely used in MPLS Traffic Engineering. Beyond the home domain. No canonical parent is asserted for Constrained Shortest Path First.

Neighborhood in Abstraction Space

Constrained Shortest Path First sits in a moderately populated region (56th percentile for distinctiveness): it has near-neighbors but no dense thicket of look-alikes.

Family — Combinatorial Optimization & Discrete Structures (31 abstractions)

Nearest neighbors

Computed from structural-signature embeddings · 2026-10-08