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What is PRECEDENCE?

April 26, 2017precedence

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What is PRECEDENCE?

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The second byte in an IPv4 header is the Type of Service (TOS) field and its original intent was to carry information which would provide quality of service features, such as prioritized delivery for IP datagrams. If you interpret the TOS field the way it was originally designed, then the first three bits in TOS byte contain the PRECEDENCE setting. Problems with the PRECEDENCE setting The Type of Service field was never widely used as originally designed and its meaning has subsequently been redefined for use by a technique called Differentiated Services (DS). This redefinition of the TOS field causes problems for the z/VM TCP/IP stack on releases of z/VM prior to 5.4.0 because one of the things it does when a packet is received is to check to make sure that the precedence setting has not changed. If the precedence setting is not what is expected, it discards the packet and resets the TCP connection. This can cause connectivity issues when packets that are destined for the z/VM TCP/IP