This patch doesn't require extra fiddling on either Linux (Gentoo) or FreeBSD 6.1.  Since both have the 8 bit array for V6 addresses, neither requires any additional OS-specific hacks.  I think this might be more generally portable.

This is a diff against the CVS archive as of today.

Index: addr_hash.c =================================================================== RCS file: /home/pdw/vcvs/repos/iftop/addr_hash.c,v retrieving revision 1.6 diff -u -r1.6 addr_hash.c --- addr_hash.c 27 Nov 2010 11:06:12 -0000 1.6 +++ addr_hash.c 5 Jun 2011 16:57:30 -0000 @@ -43,7 +43,7 @@ addr_pair* ap = (addr_pair*)key;

if (ap->af == AF_INET6) { - uint32_t* addr6 = ap->src6.s6_addr32; + uint32_t* addr6 = (uint32_t*)ap->src6.s6_addr;

hash = ( hash_uint32(addr6[0]) + hash_uint32(addr6[1]) @@ -51,7 +51,7 @@ + hash_uint32(addr6[3]) + ap->src_port) % 0xFF;

- addr6 = ap->dst6.s6_addr32; + addr6 = (uint32_t*)ap->dst6.s6_addr; hash = ( hash + hash_uint32(addr6[0]) + hash_uint32(addr6[1]) + hash_uint32(addr6[2])

Index: iftop.c =================================================================== RCS file: /home/pdw/vcvs/repos/iftop/iftop.c,v retrieving revision 1.56 diff -u -r1.56 iftop.c --- iftop.c 27 Nov 2010 11:06:12 -0000 1.56 +++ iftop.c 5 Jun 2011 16:57:30 -0000 @@ -328,11 +328,11 @@ /* First reduce the participating addresses using the netfilter prefix. * We need scratch pads to do this. */ - for (j=0; j < 4; ++j) { - scribdst.s6_addr32[j] = ip6tr->ip6_dst.s6_addr32[j] - & options.netfilter6mask.s6_addr32[j]; - scribsrc.s6_addr32[j] = ip6tr->ip6_src.s6_addr32[j] - & options.netfilter6mask.s6_addr32[j]; + for (j=0; j < 16; ++j) { + scribdst.s6_addr[j] = ip6tr->ip6_dst.s6_addr[j] + & options.netfilter6mask.s6_addr[j]; + scribsrc.s6_addr[j] = ip6tr->ip6_src.s6_addr[j] + & options.netfilter6mask.s6_addr[j]; }

/* Now look for any hits. */

Index: ns_hash.c =================================================================== RCS file: /home/pdw/vcvs/repos/iftop/ns_hash.c,v retrieving revision 1.4 diff -u -r1.4 ns_hash.c --- ns_hash.c 27 Nov 2010 11:06:12 -0000 1.4 +++ ns_hash.c 5 Jun 2011 16:57:30 -0000 @@ -29,7 +29,7 @@

int ns_hash_hash(void* key) { int hash; - uint32_t* addr6 = ((struct in6_addr *) key)->s6_addr32; + uint32_t* addr6 = (uint32_t*)((struct in6_addr *) key)->s6_addr;

hash = ( hash_uint32(addr6[0]) + hash_uint32(addr6[1])

Index: options.c =================================================================== RCS file: /home/pdw/vcvs/repos/iftop/options.c,v retrieving revision 1.46 diff -u -r1.46 options.c --- options.c 27 Nov 2010 11:06:12 -0000 1.46 +++ options.c 5 Jun 2011 16:57:30 -0000 @@ -538,16 +538,16 @@ } else { int bl, rem; - const uint32_t mm = 0xffffffff; - uint32_t part = mm; + const uint8_t mm = 0xff; + uint8_t part = mm;

- bl = n / 32; - rem = n % 32; - part <<= 32 - rem; + bl = n / 8; + rem = n % 8; + part <<= 8 - rem; for (j=0; j < bl; ++j) - options.netfilter6mask.s6_addr32[j] = htonl(mm); + options.netfilter6mask.s6_addr[j] = mm;

if (rem > 0) - options.netfilter6mask.s6_addr32[bl] = htonl(part); + options.netfilter6mask.s6_addr[bl] = part; options.netfilter6 = 1; } } @@ -560,8 +560,8 @@ } } /* Prepare any comparison by masking the provided filtered net. */ - for (j=0; j < 4; ++j) - options.netfilter6net.s6_addr32[j] &= options.netfilter6mask.s6_addr32[j]; + for (j=0; j < 16; ++j) + options.netfilter6net.s6_addr[j] &= options.netfilter6mask.s6_addr[j];

return 1; }