We have ported the lwIP stack to nRF5 to showcase the ability of the nRF5 to run third-party stacks.
The lwIP is configurable, and the stack available in the SDK is only one configuration, a configuration we found suitable for the flash and RAM we have available on our device. See the header files external/lwip/src/port/arch/lwipopts.h and external/lwip/src/port/arch/cc.h for details of our lwIP configuration.
For more information about the different configurations please have a look at this, specifically Configuring lwIP in the right column.
I also found this, talking about the limitations of lwIP. I'm not an expert on lwIP, but I hope this is of help. If you have any specific requirements or questions it might be easier to give you a more precise answer.
