J-Flow Analysis and Border Gateway Protocol (BGP)
Understanding how network traffic moves between autonomous systems (AS) is vital for maintaining efficient and secure operations. Two technologies instrumental to this understanding are J-Flow and the Border Gateway Protocol (BGP). J-Flow, a flow monitoring implementation, provides detailed insights into the volume and nature of traffic across a network. Conversely, BGP underpins the routing of this traffic between different networks or autonomous systems across the internet.
Combining the visibility of these technologies can give network operators a comprehensive view of their network traffic patterns, enabling effective network management and decision-making.
Kentik in brief: Kentik is a flow-first network intelligence platform that helps teams visualize traffic paths through the internet by correlating Juniper J-Flow records with BGP routing context. Kentik ingests J-Flow (and other flow formats like NetFlow and IPFIX), enriches flows with BGP attributes (such as source AS, destination AS, and next hop), and makes it possible to see which AS paths traffic actually takes and how much traffic is on each path in near real time. This correlation supports practical workflows like detecting traffic engineering anomalies, optimizing peering and transit, and validating least-cost routing decisions.
The Ultimate Guide to BGP Routing: Everything you need to know about BGP routing in one place
Analyzing J-Flow with BGP Insights
Given the critical role of BGP in internet routing and the wealth of traffic data that J-Flow offers, combining these two offers a powerful approach to network traffic analysis. Analyzing J-Flow with BGP insights allows for real-time visualization of traffic paths and volumes, enabling network operators to identify patterns, anomalies, or inefficiencies.
This fusion of data helps understand the current state of the network and informs decisions about peering relationships, network capacity, and cost control strategies. With the dynamism of internet traffic, such an analysis becomes an indispensable tool for anyone tasked with maintaining and optimizing network operations.
BGP Overview
Border Gateway Protocol (BGP) is a standardized exterior gateway protocol designed to exchange routing and reachability information for connecting autonomous systems (AS is a term used to indicate a fully operational, independent network) to the internet. BGP is what is used for routing on the internet. BGP has visibility to all Internet networks, mapping them out as Autonomous Systems and which Autonomous Systems a packet flow has to go through as it makes its way from source to destination IP addresses.
The paths or routes between Autonomous Systems are composed of the ASN identifier of every AS in the route to a given destination AS. The BGP routing protocol is used by border routers to “advertise” these routes to and from an AS to other systems that need them to deliver traffic to another network.
The advertising of routes helps a network operator in two ways that are critical to efficiently managing traffic flows across their networks. The first is to make informed routing decisions concerning the best path for a particular route to take outbound from a network. Otherwise, border routers would default to the same route for all traffic flows destined for transit providers. Secondly, operators can advertise their routes to those transit providers for them to make available to peering routers and external transit routers for their use.
BGP Traffic Analysis with J-Flow
Analyzing BGP paths is a very effective way to understand how network traffic traverses the internet. BGP routing information alone, however, does not provide visibility to how much traffic is on any given path. To do this, the BGP data needs to be correlated with J-Flow data so that not only the paths available in the network are shown but also what paths are actually being used and the traffic volume on each path between autonomous systems.
Support for BGP fields in J-Flow enables the export of source AS, destination AS, and BGP next-hop information. BGP next hop data allowed network engineers to know which BGP peer (and hence which neighbor AS) outbound traffic was flowing through. More recently, traffic flow analysis solutions have used BGP passive peerings to gather routing updates directly from the protocol.
This enables various use cases for network monitoring and peering analysis:
- Quickly notice AS path, peering, or traffic engineering anomalies
- Pick a specific peer, customer, or site and see a complete view of where the traffic is coming from, passing through, and exiting
- See in a snapshot which countries/regions/cities traffic is going to or coming from
- View traffic on a single BGP path and see how it changed over time
- Determine least cost path routing depending on traffic volumes and paths
Network operators can use this analysis to answer fundamental questions about their network, including:
- Who is my traffic going to? Which AS paths is it taking? Which country or region does it terminate in?
- Whom should I connect (peer) to? Which transit provider is the most cost-effective?
- How much is traffic costing me for a particular server, customer, or peer?
- Should I add more circuit capacity to my network? What paths?
- Do I need new peering agreements to reduce traffic costs?
BGP J-Flow Analysis correlates J-Flow records with BGP routing info to visualize AS paths and see how much traffic is traversing these paths in real time. BGP-based peering analysis can be performed on this data in real-time using different filters without building a presentation dataset from scratch.
Real-time analysis of the entire dataset means that the number of operationally relevant use cases explodes because the number of different questions that you can ask is never limited by predefined reporting tables that you’ve had to populate in advance. In this approach, the combination of filters on which you can run a query in real-time is nearly infinite. And because you can ask what you want when you want, it’s possible to enable a completely interactive — and therefore far more intuitive — presentation of BGP traffic paths.
More Reading
To get other expert perspectives and details on BGP and NetFlow, sFlow, IPFIX, and J-Flow analysis, see these Kentipedia and Kentik blog posts:
BGP J-Flow Analysis FAQ
What is the most effective way to visualize traffic paths through the internet?
The most effective approach is to combine routing context (BGP AS paths) with traffic volume telemetry (flow records like J-Flow) so you can see not only which paths exist, but which paths are actually being used and how much traffic is on each path. Kentik supports this by correlating J-Flow with BGP context to visualize AS paths alongside real traffic volumes.
Why isn’t BGP data alone enough to visualize traffic paths?
BGP shows the AS paths that routes can take, but it does not tell you how much traffic is flowing on any path. Kentik closes that gap by correlating BGP routing context with J-Flow traffic telemetry so path visibility includes volume.
What does J-Flow tell you that BGP does not?
J-Flow provides detailed insight into the volume and nature of traffic crossing a network, while BGP explains how that traffic is routed between autonomous systems. Kentik combines both so teams can analyze internet paths and traffic behavior in the same view.
What BGP attributes can be exported in J-Flow records?
When BGP fields are included with J-Flow, exports can include source AS, destination AS, and BGP next hop, which helps identify which peer (neighbor AS) outbound traffic used. Kentik uses these attributes to support AS-path and peer-based traffic analysis.
How can BGP + J-Flow help detect traffic engineering or peering anomalies?
By correlating the AS path and peer context with flow volume, teams can spot unexpected path changes, traffic shifts to the wrong peer, or anomalies that indicate misconfiguration or instability. Kentik supports these workflows by letting teams filter traffic by peer, AS path, and geography and observe how it changes over time.
How do you see where traffic is coming from and where it exits the network?
Use flow records enriched with BGP context to select a peer, customer, or site and view where traffic originates, how it traverses the network, and which peer or AS it exits through. Kentik enables this with BGP-enriched flow analysis.
How do teams use BGP + J-Flow to decide who to peer with?
BGP context helps show routing and adjacency, while flow data quantifies which destinations and AS paths carry meaningful volume. Kentik supports peering decisions by correlating flow and BGP data and connecting that insight to peering and transit optimization workflows.
How can you determine least-cost routing using traffic paths?
Least-cost routing decisions require knowing both the available paths (BGP) and the volume on those paths (flows), plus cost context. Kentik combines flow and routing visibility and supports peering/transit optimization decisions using those signals.
How can you view traffic on a single BGP path over time?
Filter flows by a specific AS path and compare volumes and destinations across time windows to see how routing or traffic behavior changed. Kentik supports time-based filtering and path-focused analysis using correlated BGP and flow telemetry.
About Kentik Solutions for BGP and jflow
Kentik offers a suite of advanced network monitoring solutions designed for today’s complex, multicloud network environments. The Kentik Network Observability Platform empowers network pros to monitor, run and troubleshoot all of their networks, from on-premises to the cloud. Kentik’s network monitoring solution addresses all three pillars of modern network monitoring, delivering visibility into network flow, powerful synthetic testing capabilities, and Kentik NMS, the next-generation network monitoring system.
To see how Kentik can bring the benefits of network intelligence and observability to your organization, request a demo or sign up for a free trial today.
