Note: I'm perfectly happy for this table and associated information to be used anywhere by anyone, that's why it's been published here, I couldn't find an easy reference, so I created one and published it for everyone, but, if you do republish the information, please attribute the source and don't try to pass it off as original work. Thanks.

 

You have a DSCP tag on your packets, but, you can only see ToS when capturing packets? How do you work out which ToS value equates to which DSCP value? Or... You are tagging using DSCP/PHB classes but only seeing DSCP hex or decimal tags on your packets? What does it all mean? 

 

The following table shows common decimal, hex and binary values for TOS, broken down into the meaning of the parts of that byte including DSCP values when interpretting that byte as DSCP.

 

So, there you have it, one byte in a packet header, two ways to look at it...

If dealing with TOS (Type of Service), the first 3 bits indicate the precedence, the 4th bit indicates the whether or not low delay is preferred, the 5th bit indicates whether or not high throughput is preferred, the 6th bit indicates whether or not high reliability is preferred and the 7th and 8th bits are reserved... More info can be found in RFC 791, written in 1981, which defines IP.

If dealing with DSCP (Differentiated Services (Diffserv) Codepoint) only the first 6 bits are used and the last 2 are ignored... More info can be found in RFC 2474, written in 1998, which defines the Differentiated Services Field (DS Field) which is what the TOS byte is referred to when talking about differentiated services and specifically DSCP. Also, RFC 2597 and RFC 3246 which define some of the PHB (Per-hop Behaviour) classes may be useful reading...