Header Fields

• Version (4 bits)

• • 6
  • Differentiation of v4 vs. v6 is preferably performed on the link layer

• Traffic class (1 byte)

• • Like IP ToS byte, but with new Diffserv interpretation

• Flow label (20 bits)

• • Allows the sender to encode layer 4 or application routing information
  • Useful when layers 4 and up are encrypted (IPsec)
  • Usage is a point of controversy (poor man’s MPLS?) so currently set to 0