Brocade TurboIron 24X Series Configuration Guide - Manual (Page 702)

668 Brocade TurboIron 24X Series Configuration Guide
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Memory considerations
• Add, change, or negate route maps (when used by the network command or a redistribution
command).
After resetting neighbor sessions
The following parameter changes take effect only after the router BGP4 sessions are cleared, or
reset using the “soft” clear option. (Refer to
“Closing or resetting a neighbor session” on
page 764.)
The parameter are as follows:
• Change the Hold Time or Keep Alive Time.
• Aggregate routes.
• Add, change, or negate filter tables.
After disabling and re-enabling redistribution
The following parameter change takes effect only after you disable and then re-enable
redistribution:
• Change the default MED (metric).
Memory considerations
BGP4 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 to
hold 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 memory
allocation for BGP4 data. These devices automatically allocate memory when needed to support
BGP4 neighbors, routes, and route attribute entries. Dynamic memory allocation is performed
automatically by the software and does not require a reload.
The memory amounts, including routes received from neighbors, BGP route advertisements (routes
sent to neighbors), and BGP route attribute entries. The routes sent to and received from
neighbors use the most BGP4 memory. Generally, the actual limit to the number of neighbors,
routes, or route attribute entries the device can accommodate depends on how many routes 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 (about
80,000 routes), the memory can support a larger number of BGP4 neighbors. However, if most of
the BGP4 neighbors send or receive full BGP route tables, the number of BGP neighbors the
memory 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 150 –
200 neighbors, with the assumption that the Layer 3 Switch receives about one million routes total
from all neighbors and sends about eight million routes total to neighbors. For each additional one
million incoming routes, the capacity for outgoing routes decreases by around two million.