Snort isn't able to read large pcap files (> 2GB) if you compile it with

$ ./configure
$ make
$ make install

Even if the libpcap shipped with your distribution is able to read big files. The snort source does need to be compiled with the compile time opions _LARGEFILE_SOURCE, _LARGEFILE64_SOURCE and _FILE_OFFSET_BITS=64. You can enable these flags by setting the environment varible CFLAGS

$ CFLAGS="-D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64" ./configure
$ make
$ make install