H3C S5120-EI Series Operation Manual

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H3C S5120-EI Series Operation Manual Manual pdf 555 page image

3-13 Priority MappingWhen configuring priority mapping, go to these sections for information you are interested in:z Priority Overviewz Priority Mapping Overviewz Configuring a Priority Mapping Tablez Configuring the Port Priorityz Configuring Port Priority Trust Modez Displaying and Maintaining Priority MappingPriority OverviewThe following describes several types of precedence:1) IP precedence, ToS precedence, and DSCP precedenceFigure 3-1 DS field and ToS fieldThe ToS field in an IP header contains eight bits, which are described as follows:z The first three bits indicate IP precedence in the range of 0 to 7.z Bit 3 to bit 6 indicate ToS precedence in the range of 0 to 15.z RFC2474 re-defines the ToS field in the IP packet header, which is called the DS field. The first six(bit 0 to bit 5) bits of the DS field indicate DSCP precedence in the range of 0 to 63. The last two bits(bit 6 and bit 7) are reserved bits.Table 3-1 Description on IP PrecedenceIP Precedence (decimal) IP Precedence (binary) Description0 000 Routine1 001 priority2 010 immediate3 011 flash4 100 flash-override5 101 critical