Re: 0xc0

[Default Debian Reader <debianuser@jkeating.static.execpc.com>]

On Thu, 10 Sep 1998, Nathan E Norman wrote:

> On Thu, 10 Sep 1998, Default Debian Reader wrote:
> 
>  : Anyone tell me what tos 0xc0 is in ip headers?
> 
> First, install the doc-iana package.
> 
> I'm no IP expert (I'm currently reading Stevens's IP Illustrated book)
That book was copyright 1994, i imagine it was printed even before that.
> but if you are referring to the Type Of Service field, 0xc0 is not a
> valid choice.
> 
That is my question, Is it valid because i have seen ip headers with a tos
of 0xc0 or at least it appeared.

> [ from /usr/doc/doc-iana/assignments/ip-parameters.gz ]
> 
> TOS Value       Description                             Reference
> ---------       --------------------------              ---------
>   0000          Default                                 [RFC1349]
>   0001          Minimize Monetary Cost                  [RFC1349]
>   0010          Maximize Reliability                    [RFC1349]
>   0100          Maximize Throughput                     [RFC1349]
>   1000          Minimize Delay                          [RFC1349]
>   1111          Maximize Security                       [RFC1455]
> 
> The TOS value is used to indicate "better".  Only one TOS value or
> property can be requested in any one IP datagram.
> --
> 
> Note that the TOS field is an eight-bit field composed of a three-bit
> precedence field, the 4-bit field described above, and one unused bit.
> This is confusing since a TOS "value" of 0001 is written in hex as 0x02.
> 
> 0xc0 would be 011000000, so two bits in the precedence field have been
> set (and none of the TOS bits).  According to Stevens, the precedence
> field is ignored, so I'm not sure what's going on here :)
> 
> --
> Nathan Norman
> MidcoNet  410 South Phillips Avenue  Sioux Falls, SD
> mailto:finn@midco.net           http://www.midco.net
> finger finn@home.midco.net for PGP Key: (0xA33B86E9)
> 
> 
>