Combine beef, garlic, ginger, cinnamon and 2 quarts water. Bring to a boil, skim off scum. Reduce heat to low and simmer gently until meat is tender, about 45 minutes. Continue skimming and keeping level of liquid constant by replenishing with fresh water. Meanwhile, rinse and chop the cilantro. When meat is tender, remove garlic, cinnamon and ginger. Add noodles and simmer until tender, about 5 minutes. Remove soup from heat, stir in salt, lime juice, bean sprouts, pepper and cilantro. Adjust seasoning and serve piping hot.