```make install```: download, compile, install lwip2

```make latestmaster```: download latest lwip2, compile, install

```make latestupstream```: download latest lwip2 and latest upstream lwIP, compile, install

```make download```: download lwIP-2 builder

```make clean```: clean builder only

glue and lwIP debug options are in builder/glue/gluedebug.h

MSS values are in builder/Makefile.arduino

MSS values in boards.txt are only informative
