LINK RANK AND BGP(BORDER GATEWAY PROTOCOL)
Link Rank is a set of graphical tools developed to understand the true dynamics of BGP and to interpret the multiple gigabytes of BGP log data. So what is BGP for you? Internet has a lot of autonomous systems. BGP (Border Gateway Protocol) is there to exchange reachability information between autonomous systems. It acts as a service provider to manage the networks.
If you want to understand and learn more about BGP routing dynamics then link-rank is the right tool for you. Link-Rank helps to summarize the megabytes of BGP in the form of graphs. Rank-Change graph of link-rank clearly shows that which AS-AS has gained routes and which has lost routes.
Link-Rank Graph And Rank Change Graphs
Link-Rank and Rank-Change graphs represents large scale path dynamics in simple and easy form. The BGP updates messages about the complete path used to reach the final destination. This path information is used for capturing BGP dynamics.
Furthermore it is difficult for the autonomous systems. To reach the destinations it detects which links are heavily used . So with the help of link-rank graphs it is easy to understand the high rank edges which carry maximum number of routes to other destinations.
To construct a Rank-Change graph you have to trace link-rank graph over time. In addition you have to associate weight of edges with the difference of weights of individual link. Negative link shows that you have lost the route and positive link shows the gaining of routes in the given time. Only if the link weight shows the absolute link value then the client displays the Rank-Change graph.
So in the figure, from the perspective of router AS 7018 is the Rank-Change graph. Red line indicates the loss of routes and green shows the gaining of routes. From AS 7018 to AS 3320, 53 routes loss took place. Consequently the loss routes shifts to other links by AS 5511. The first value shown in each link is the Link-Rank and the figures in bracket shows the changes in ranks. Because of this graph the Link-Rank users can easily understand the routing changes caused by network.
Using Link Rank To Understand Routing Changes
It have two purposes:
- To show what happened on the Internet in the given time period
- Further for isolating the cause of routing changes
To understand the routing changes follow these 3 steps :
- Understanding Routing Dynamics: In the figure above the AS 7018 is the period of high activity. When we sequence it with the help of link-rank animations, it can be seen at this point of time the route is switched to other paths. This time period generated thousands of updates. With the help of link-rank it is possible to summarize them all in one point.
- Identifying Cause Of Change: Link-Rank is used to tell the nature of dynamics and to perform diagnosis. In the figure, 53 routes loss take place from AS 7018 to AS 3320 and shifts to the AS 5111. This problem might have arise due to problem or due to recovery from previous problem. Link-Rank requires a lot of view points to diagnose the problem in routing.
- Assembling Multiple Views: Furthermore Link-Rank requires multiple views to assemble a problem. Often different monitoring points relates to each other in routing changes. The relation requires multiple view points for observation. In addition by link-rank tool you can assemble multiple observations in a single window.