1. **State the problem:** Simplify the expression $\frac{2}{7} \div \frac{6}{21}$. 2. **Recall the division rule for fractions:** Dividing by a fraction is the same as multiplying by its reciprocal. So, $$\frac{2}{7} \div \frac{6}{21} = \frac{2}{7} \times \frac{21}{6}.$$ 3. **Multiply the fractions:** Multiply the numerators and denominators: $$\frac{2 \times 21}{7 \times 6} = \frac{42}{42}.$$ 4. **Simplify the fraction:** $$\frac{\cancel{42}}{\cancel{42}} = 1.$$ 5. **Final answer:** The simplified value of $\frac{2}{7} \div \frac{6}{21}$ is $1$.