PowerConnect B-Series FCX Configuration Guide 99153-1002266-01Memory considerations 30After disabling and re-enabling redistributionThe following parameter change takes effect only after you disable and then re-enableredistribution:• Change the default MED (metric).Memory considerationsBGP4 handles a very large number of routes and therefore requires a lot of memory. For example,in a typical configuration with just a single BGP4 neighbor, a BGP4 router may need to be able tohold up to 80,000 routes. Many configurations, especially those involving more than one neighbor,can require the router to hold even more routes. Layer 3 Switches provide dynamic memoryallocation for BGP4 data. These devices automatically allocate memory when needed to supportBGP4 neighbors, routes, and route attribute entries. Dynamic memory allocation is performedautomatically by the software and does not require a reload.The memory amounts for all BGP4 data, including routes received from neighbors, BGP routeadvertisements (routes sent to neighbors), and BGP route attribute entries. The routes sent to andreceived from neighbors use the most BGP4 memory. Generally, the actual limit to the number ofneighbors, routes, or route attribute entries the device can accommodate depends on how manyroutes the Layer 3 Switch sends to and receives from the neighbors.In some cases, where most of the neighbors do not send or receive a full BGP route table (about80,000 routes), the memory can support a larger number of BGP4 neighbors. However, if most ofthe BGP4 neighbors send or receive full BGP route tables, the number of BGP neighbors thememory can support is less than in configurations where the neighbors send smaller route tables.As a guideline, Layer 3 Switches with a 512 MB Management 4 module can accommodate 150through 200 neighbors, with the assumption that the Layer 3 Switch receives about one millionroutes total from all neighbors and sends about eight million routes total to neighbors. For eachadditional one million incoming routes, the capacity for outgoing routes decreases by around twomillion.Memory configuration options obsoleted bydynamic memoryDevices that support dynamic BGP4 memory allocation do not require or even support staticconfiguration of memory for BGP4 neighbors, routes, or route attributes. Consequently, thefollowing CLI commands and equivalent Web management options are not supported on thesedevices:• max-neighbors • max-routes • max-attribute-entries If you boot a device that has a startup-config file that contains these commands, the softwareignores the commands and uses dynamic memory allocation for BGP4. The first time you save thedevice running configuration (running-config) to the startup-config file, the commands are removedfrom the file.
