lwIP provides a way to define your own custom memory pools to be used in addition to the standard ones provided by lwIP. There are two reasons you may need to do this: 1. * You want to use a pool-based mem_malloc, as described in the next section 2. * You want to add extra pools for your architecture (for example, you have a custom IP protocol, or your sys_arch requires extra data structures not explicitly provided already, or you are using lwIP's memory pool manager in your OS or application).