An example from Mao Essay
An example from Mao
Route flap damping is a technique used to help maintain a stable network by withdrawing nodes from the routing table when the nodes ‘flap’ between being available and being unavailable. However, recent work has shown that route flap damping can cause extensive increases in convergence time . The reason for this phenomenon appears to be that when the flap dampening protocol causes a route to be with drawn and simultaneously isolates a destination, GPB contuse to explore alternate routes with no hope of finding an active route to the destination.
Under this circumstance, the nodes between the source and isolated destination may not reach convergence until the path to the destination is restored. An example from Mao  illustrating this behaviour for a local network (figure 2. 2) is described in table 2. III. Figure 2. 2  In figure 2. 2, d is the destination and is connected to the remainder of the network through node 1. However, node one is flapping and is removed from the routing tables, as shown in table 2. III. Table 2. III  The * refers to an active route for the hop from the specific router toward the destination.
The – refers to a route withdrawn from the routing table. For example, in the steady state routing table, the best path for all the routers to d is to have the next hop to 1. Thus 1* is shown in all the routing tables, as opposed to 41 (hop to 4 then a hop to 1). At the first step, node 1 announces that it is unavailable because of the flap damping protocol, so it is removed from the routing table for all the remaining 4 nodes. The subsequent announcements shown in table 2. III illustrate the number of communications that must occur in order for the network to be convinced that there is no alternate route to d.
Of course, the path-vector algorithm used by BGP only requires communication between neighbouring nodes, which is inherently slow to converge even if the system is functioning properly. The scalability of BGP is limited by the router hardware resource utilisation associated with inter-router communication and route data storage. Li  has pointed out that “ The resource consumption of BGP router consists two components…: 1) CPU consumption in BGP session establishment, route selection, routing information processing, and
handling of routing updates; 2) Router memory to install routes and multiple paths associated with the routes. Thus, the volume of routes directly affects BGP scalability, as well as the number of BGP sessions and the complexity of routing policies. ” Thus, it is apparent that there are real physical limitations of BGP scalability. BGP exhibits a low efficiency in finding the transmission path that is truly going to give the best possible transmission. This is because traffic load is not considered as one of the metrics in obtaining a routing solution.
Also, because BGP allows for certain local policies without regard to what effects may result for the global optimization problem, the innate efficiency of BGP is limited by decisions of local network managers. The security of Internet routing is limited by the ability of BGP to verify that advertised routes are valid or to control route announcements. To be specific, there is no protocol that prevents an AS from advertising an arbitrary Internet address or to know if an AS has the authorisation to announce a certain address. Thus, there is no way to guarantee the final destination of a data packet.
University/College: University of Arkansas System
Type of paper: Thesis/Dissertation Chapter
Date: 17 May 2017
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