CURRENT BGP PROBLEMS
AND SUGGESTED SOLUTIONS
CS526- Assignment# 4
University of Missouri- Kansas City
The Border Gateway Protocol (BGP) is an exterior gateway protocol (EGP) also known as inter-Autonomous System routing protocol. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information on the list of Autonomous Systems (ASs) that reachability information traverses. This information is sufficient to construct a graph of AS connectivity from which routing loops may be pruned and some ...view middle of the document...
RRC depends on RR in learning and advertising routes. RRs are connected in a full mesh. RRs do not readvertise prefixes between non-clients. Two more attributes are added which are, ORIGINATOR_ID(9) and CLUSTER_LIST(10). It allows a router (route reflector – RR) to advertise routes received from an iBGP peer to other iBGP peers between clients and from clients to non-clients, and vice versa. The basic purpose of ORIGINATOR_ID and CLUSTER_LIST attributes is to perform loop detection. This provides a scalable alternative to an iBGP full mesh.
b) AS Confederation: This technique is based on Divide and conquer paradigm that is, divide an AS into sub-Ass and within a sub-AS use full mesh I-BGP and between sub-Ass uses full mesh E-BGP. Here we subdivide the autonomous systems with a very large number of BGP speakers into smaller domains for purposes of controlling routing policy via information contained in the BGP AS_PATH attribute. Subdividing a large autonomous system allows a significant reduction in the total number of intra-domain BGP connections, as the connectivity requirements simplify to the model used for inter-domain connections and thus help in avoiding I-BGP full mesh.
c) Virtual Peering: Virtual peering is used to reduce the overhead and management complexity of maintaining numerous direct BGP/IDRP sessions which otherwise might be required or desired among routers within a single routing domain as well as among routers in different domains that are connected to a common switched fabric (e.g. an ATM cloud). It proposes to use IDRP/BGP Route Servers, which would relay external routes with all of their attributes between client routers. The clients would maintain IDRP/BGP sessions only with the assigned route servers (sessions with more than one server would be needed if redundancy is desired). The Route Server would propagate all routes that are received from a client router to other clients. Since all external routes and their attributes are relayed unmodified between the client routers, the client routers would acquire the same routing information as they would via direct peering. Therefore, this arrangement is referred to as virtual peering.
Instability Issue (Route Flapping):
A Route Flap may be described as constant up and down of a link. A widely deployed BGP implementation may tend to fail due to high routing update volume of the advertised reachability of a subset of Internet prefixes. Two methods of controlling the frequency of route advertisement are described here. The first method involves fixed timers. The fixed timer technique has no space overhead per route but has the disadvantage of slowing route convergence for the normal case where a route does not have a history of instability. The second method overcomes this limitation at the expense of maintaining some additional space overhead. The additional overhead includes a small amount of state per route and a very small processing overhead.