entries created for each VPN

For a layer-3 solution, the maximum number of routes that could be stored on a given PE is also a constraint. This is due to the fact that a PE router stores routes from all the VPNs that it carries. To alleviate the impact of this factor on the scalability of the solution, route summarization could be used whenever possible. For a layer-2 solution, the maximum number of layer-2 forwarding table entries supported on a PE routes is also a constraint. The PE router has to create those entries in order to be able to perform its layer-2 switching functionality. The impact of this factor on scalability could be alleviated by requiring that CE devices be routers, and/or applying limits to the number of (MAC) entries created for each VPN – to avoid having a customer VPN overwhelm the PE routers with a large number of source MAC addresses. Deployment Deployment of a layer-3 solution usually requires high end LSRs capable of handling multiple routing and forwarding tables at the provider edge. It also requires that BGP peering be set up between the these routers. If the service provider is already using BGP so extensively throughout there network, as in the case of ISPs or large IP carriers, then they might prefer going with a layer-3 solution since it allows them to take advantage of the already available BGP sessions, and the already available BGP know how. Then, of IP/MPLS-Based VPNs Layer-3 vs. Layer-2   Page 14 of 16 FOUNDRY NETWORKS WHITE PAPERcourse, LSPs between the PEs have to be set up for carrying traffic between the PEs. When leveraging the existing BGP peering session, however, some changes to route reflection clusters might be required, so that no route reflector would be overwhelmed by too many routes from too many VPNs. Should the provider be using a confederation, then the problem becomes similar to the inter-provider (inter-AS) problem, where the VPNs have to span multiple autonomous systems. Also, similar to the route reflection case, the provider needs to carefully consider what could be done in order to avoid having the routers connecting the member-ASes overwhelmed by too many routes.

entries created for each VPN

For a layer-3 solution, the maximum number of routes that could be stored on a given PE is also a constraint. This is due to the fact that a PE router stores routes from all the VPNs that it carries. To alleviate the impact of this factor on the scalability of the solution, route summarization could be used whenever possible. For a layer-2 solution, the maximum number of layer-2 forwarding table entries supported on a PE routes is also a constraint. The PE router has to create those entries in order to be able to perform its layer-2 switching functionality. The impact of this factor on scalability could be alleviated by requiring that CE devices be routers, and/or applying limits to the number of (MAC) entries created for each VPN – to avoid having a customer VPN overwhelm the PE routers with a large number of source MAC addresses. Deployment Deployment of a layer-3 solution usually requires high end LSRs capable of handling multiple routing and forwarding tables at the provider edge. It also requires that BGP peering be set up between the these routers. If the service provider is already using BGP so extensively throughout there network, as in the case of ISPs or large IP carriers, then they might prefer going with a layer-3 solution since it allows them to take advantage of the already available BGP sessions, and the already available BGP know how. Then, of IP/MPLS-Based VPNs Layer-3 vs. Layer-2   Page 14 of 16 FOUNDRY NETWORKS WHITE PAPERcourse, LSPs between the PEs have to be set up for carrying traffic between the PEs. When leveraging the existing BGP peering session, however, some changes to route reflection clusters might be required, so that no route reflector would be overwhelmed by too many routes from too many VPNs. Should the provider be using a confederation, then the problem becomes similar to the inter-provider (inter-AS) problem, where the VPNs have to span multiple autonomous systems. Also, similar to the route reflection case, the provider needs to carefully consider what could be done in order to avoid having the routers connecting the member-ASes overwhelmed by too many routes.