[c-nsp] ToS equivalent to IP Precedence?

[Amol Sapkal]

Hi,
Referring to below link and my experience with SAA configurations,
http://www.cisco.com/warp/public/105/dscpvalues.html

DSCP is represented by the 6 significant bits. Of this, the 3
significant bits are IP Precedence. ToS is represented by the entire 8
bits.

So,

If you need to configure a IP precedence of 5, the tos value should be:
101 110 00 i.e 184

The above will be called as DSCP 46 (note that DSCP is only the 6
significant bits).

Similarly, an IP precedence of 1 will be dscp 001000 and tos 00100000
(32). A ToS of 32 would be equal to a precedence of 1.






On Tue, 14 Dec 2004 09:21:30 -0000, Tim Franklin <tim at colt.net> wrote:
> Hi Dave,
> 
> 
> 
> cisco-nsp-bounces at puck.nether.net wrote:
> > Noting that the range of ToS bits is 0-255, is there a way to directly
> > equate a ToS bit of say, 8, to an IP precedence?  My understanding is
> > that a ToS of 8 is equal to precedence 1?  Is this correct?  I may be
> > way off...
> >
> > I have a situation where I can reflect the ToS bit into a tunneled
> > packet but I'm trying to figure out how to set the ToS bit so that I
> > can do things prec-based.
> 
> It's easiest if you draw it:
> 
> "Old-world" QoS is:
> 
> P2 | P1 | P0 | T3 | T2 | T1 | T0 | NA
> 
> P2-P0 are IP precedence, T3-T0 are the old-style "ToS" (least-cost,
> low-latency, high-bandwidth etc), NA is not used.
> 
> DSCP QoS is:
> 
> D5 | D4 | D3 | D2 | D1 | D0 | NA | NA
> 
> D5-D0 are DSCP values, NA is not used.  (Actually, I seem to remember
> someone pointed out last time this came up that there *is* now an RFC
> defining a use for the two LSBs, but I don't recall what it is, and by the
> sound of things it's not important in your case.)
> 
> If you fill in the bit patterns for the items you want, it's fairly easy to
> swap about between IP-prec, "TOS byte" and DSCP.
> 
> Regards,
> Tim.
> 
> --
> ____________   Tim Franklin                 e: tim at colt.net
> \C/\O/\L/\T/   Product Engineering Manager  w: www.colt.net
> V  V  V  V    Managed Data Services        t: +44 20 7863 5714
>                                            f: +44 20 7863 5876
> 
> 
> 
> 
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-- 
Warm Regds,

Amol Sapkal

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