these two segfault immediately every time..

Core was generated by `tcpsic -s 192.168.42.42 -d 192.168.42.22 -p 10000'.
Program terminated with signal 11, Segmentation fault.
#0  libnet_in_cksum (addr=0xc, len=<optimized out>) at libnet_checksum.c:74
74	        sum += *addr++;
(gdb) bt
#0  libnet_in_cksum (addr=0xc, len=<optimized out>) at libnet_checksum.c:74
#1  0x00000030fb80cc09 in libnet_inet_checksum (l=0x1e6d010, iphdr=<optimized out>, protocol=<optimized out>, h_len=185, beg=<optimized out>, end=<optimized out>)
    at libnet_checksum.c:277
#2  0x0000000000401a3b in main (argc=<optimized out>, argv=<optimized out>) at tcpsic.c:321

udpsic fails in a similar way...

Program terminated with signal 11, Segmentation fault.
#0  libnet_in_cksum (addr=0xc, len=<optimized out>) at libnet_checksum.c:74
74	        sum += *addr++;
(gdb) bt
#0  libnet_in_cksum (addr=0xc, len=<optimized out>) at libnet_checksum.c:74
#1  0x00000030fb80ca17 in libnet_inet_checksum (l=0x89a010, iphdr=<optimized out>, protocol=<optimized out>, h_len=139, beg=<optimized out>, end=<optimized out>)
    at libnet_checksum.c:307
#2  0x0000000000401919 in main (argc=<optimized out>, argv=<optimized out>) at udpsic.c:304