ripng_print(netdissect_options *ndo, const u_char *dat, unsigned int length)
{
	register const struct rip6 *rp = (const struct rip6 *)dat;
	register const struct netinfo6 *ni;
	register u_int amt;
	register u_int i;
	int j;
	int trunc;

	if (ndo->ndo_snapend < dat)
		return;
	amt = ndo->ndo_snapend - dat;
	i = min(length, amt);
	if (i < (sizeof(struct rip6) - sizeof(struct netinfo6)))
		return;
	i -= (sizeof(struct rip6) - sizeof(struct netinfo6));

	switch (rp->rip6_cmd) {

	case RIP6_REQUEST:
		j = length / sizeof(*ni);
		if (j == 1
		    &&  rp->rip6_nets->rip6_metric == HOPCNT_INFINITY6
		    &&  IN6_IS_ADDR_UNSPECIFIED(&rp->rip6_nets->rip6_dest)) {
			ND_PRINT((ndo, " ripng-req dump"));
			break;
		}
		if (j * sizeof(*ni) != length - 4)
			ND_PRINT((ndo, " ripng-req %d[%u]:", j, length));
		else
			ND_PRINT((ndo, " ripng-req %d:", j));
		trunc = ((i / sizeof(*ni)) * sizeof(*ni) != i);
		for (ni = rp->rip6_nets; i >= sizeof(*ni);
		    i -= sizeof(*ni), ++ni) {
			if (ndo->ndo_vflag > 1)
				ND_PRINT((ndo, "\n\t"));
			else
				ND_PRINT((ndo, " "));
			rip6_entry_print(ndo, ni, 0);
		}
		break;
	case RIP6_RESPONSE:
		j = length / sizeof(*ni);
		if (j * sizeof(*ni) != length - 4)
			ND_PRINT((ndo, " ripng-resp %d[%u]:", j, length));
		else
			ND_PRINT((ndo, " ripng-resp %d:", j));
		trunc = ((i / sizeof(*ni)) * sizeof(*ni) != i);
		for (ni = rp->rip6_nets; i >= sizeof(*ni);
		    i -= sizeof(*ni), ++ni) {
			if (ndo->ndo_vflag > 1)
				ND_PRINT((ndo, "\n\t"));
			else
				ND_PRINT((ndo, " "));
			rip6_entry_print(ndo, ni, ni->rip6_metric);
		}
		if (trunc)
			ND_PRINT((ndo, "[|ripng]"));
		break;
	default:
		ND_PRINT((ndo, " ripng-%d ?? %u", rp->rip6_cmd, length));
		break;
	}
	if (rp->rip6_vers != RIP6_VERSION)
		ND_PRINT((ndo, " [vers %d]", rp->rip6_vers));
}
The software reads data past the end, or before the beginning, of the intended buffer.