Place corned beef in a large pot of cold water and bring to boil.  Cover and simmer for 2 hours.  Add onions, carrots and potatoes and simmer 30-40 more minutes until potatoes are tender.  Remove meat and slice.  Arrange meat and vegetables on a platter.  Keep warm.  Turn up heat under pot.  When water boild, add cabbage.  Boil for 3-5 minutes and drain.  Place cabbage on the serving platter.  I like to serve this with a couple different mustards and green beer.