Due to a problem of NicheStack TCP/IP Stack - Nios® II Edition, a misaligned memory trap happens when a multicast message is sent and a stream of multicast messages are being received at the same time.
Download two text files, pk_alloc.c and ip_write_internal.c, and update pktalloc.c and ip.c files with them to handle multicast messages correctly. This issue will be fixed in the future version of Quartus® II software.
1. pk_alloc.c
Update <install_dir>/nios2eds/components/altera_iniche/UCOSII/src/net/pktalloc.c with pk_alloc.c
2. ip_write_internal.c
Update <install_dir>/nios2eds/components/altera_iniche/UCOSII/src/ip/ip.c with ip_write_internal.c