8/13/2023 0 Comments Bgp full meshThe reflectors have iBGP sessions with one another, and with each client.Ī reflector in one cluster can simultaneously be a client in a hierarchically higher cluster, as long as the protocol messages in each cluster are disambiguated with a cluster identifier parameter.īoth major techniques can suffer from instability unless you use an OSPF-like rule. To improve fault tolerance, there can be more than one reflector. Route reflection improves iBGP scalability by removing the need to have a full mesh of BGP sessions among all routers in the AS it allows the creation of hierarchies of routers, with full mesh only on the "route servers" in each "cluster" of BGP speakers.Ī basic cluster has a reflector that connects, in a full mesh, to all other iBGP nodes not in clusters, and some number of route reflector clients, which have iBGP sessions with the reflector but none outside the reflector cluster. There must be full iBGP meshing inside the cluster, but only the route reflector server needs to peer, via iBGP, with other iBGP speakers (including other clusters) inside the AS. Route reflector clusters have at least one route reflector that acts as a server to other iBGP speakers within the cluster, and some number of route reflector clients. Session maintenance, both of the BGP session proper and the TCP connection over which it runs, are processor-intensive and may require more powerful router control plane hardware.īGP route reflector introduce hierarchy, a well-recognized means of scaling, into iBGP. The basic rule of iBGP is that all BGP speakers within an AS must peer with one another, which leads to an exponential growth of BGP sessions. The methods can be used in conjunction with one another. Two techniques, route reflectors and BGP confederations can reduce the need for the high overhead of full meshing. One of the major scalability problems of BGP running over TCP is that TCP takes a substantial amount of processing, as can the per-interface issues of BGP setup, advertising, and acceptance. Configurations would be very big considering all the lines needed to setup the full mesh.A route reflector is a technique for interconnecting Border Gateway Protocol (BGP) routers, inside an autonomous system, to improve scalability. Namely, a large number of IBGP sessions might consume a significant amount of bandwidth.Īdding a new device to the network means reconfiguring all the existing devices. So, the solution is not so scalable, can get pretty complex with a large number of IBGP peers, and has the potential to affect the performance of the overall network. Logically, as the number of routers increases, so does the number of BGP sessions required to establish a full mesh of IBGP peers. The BGP split-horizon rule prevents ROUTER B from propagating routes learned from ROUTER A to ROUTER C. This rule states that any route received from an iBGP neighbor must not be advertised to any other iBGP neighbor.The inconsistent routing tables can cause routing loops or routing black holes. If the originating IBGP router is not fully-meshed with every IBGP neighbor, the IBGP neighbors that are not peering with the originating IBGP router will have different IP routing tables than the IBGP neighbors that are peering with the IBGP router that received the original BGP update from the external AS. The main reason that an AS needs to fully mesh its IBGP neighbors is due to the BGP split-horizon rule that prevents routing loops or routing black holes.
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