Compiles successfully on FreeBSD, but segfaults when run as server. about pwnat HOT 5 OPEN

[root@srv pwnat-master]# make
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o socket.o socket.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o message.o message.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o strlcpy.o strlcpy.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o client.o client.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o packet.o packet.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o list.o list.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o destination.o destination.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o udpserver.o udpserver.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX   -c -o udpclient.o udpclient.c
gcc -Wall -Wshadow -Wpointer-arith -Wwrite-strings -D LINUX -o pwnat pwnat.c socket.o message.o strlcpy.o client.o packet.o list.o destination.o udpserver.o udpclient.o
[root@srv pwnat-master]# ./pwnat -s
Segmentation fault (core dumped)
[root@srv pwnat-master]# gcc -v
Using built-in specs.
Target: x86_64-redhat-linux
Configured with: ../configure --prefix=/usr --mandir=/usr/share/man --infodir=/usr/share/info --with-bugurl=http://bugzilla.redhat.com/bugzilla --enable-bootstrap --enable-shared --enable-threads=posix --enable-checking=release --with-system-zlib --enable-__cxa_atexit --disable-libunwind-exceptions --enable-gnu-unique-object --enable-languages=c,c++,objc,obj-c++,java,fortran,ada --enable-java-awt=gtk --disable-dssi --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-1.5.0.0/jre --enable-libgcj-multifile --enable-java-maintainer-mode --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --disable-libjava-multilib --with-ppl --with-cloog --with-tune=generic --with-arch_32=i686 --build=x86_64-redhat-linux
Thread model: posix
gcc version 4.4.7 20120313 (Red Hat 4.4.7-4) (GCC)