4.2. Label Types

4.2. Label Types

The first 2 bits of a wire format domain label are used to denote the type of the label. [RFC1035] allocates 2 of the 4 possible types and reserves the other 2. More label types were defined in [RFC2671]. The use of the 2-bit combination defined by [RFC2671] to identify extended label types remains valid. However, it should be noted that the use of extended label types has been problematic in practice. This document deprecates extended label types; their use in the future SHOULD NOT be assumed to be supported.