Standard IP Precedence values IP Precedence Decimal value Bit pattern

Table B-2 shows the standard IP TOS values, as defined in RFC 1349. The idea was that an application could use these bits to request the appropriate forwarding behavior. Because the values are specified in different bits, the standard originally allowed applications to specify more than one option. This turned out to be unmanageable in practice because it wasn't clear which bit should have precedence in cases where two bits were set, and each would result in selecting different paths. So the standard was changed in RFC 1349 to prevent combinations of TOS bits.