BCP regarding TOS transparancy for internet traffic

Wed May 25 17:39:38 UTC 2005

On Wed, 25 May 2005, Eric A. Hall wrote:

>
>
> On 5/25/2005 7:08 AM, Mikael Abrahamsson wrote:
>>
>> I've been debating whether the TOS header information must be left
>> untouched by an ISP, or if it's ok to zero/(or modify) it for internet
>> traffic. Does anyone know of a BCP that touches on this?
>>
>> My thoughts was otherwise to zero TOS information incoming on IXes,
>> transits and incoming from customers, question is if customers expect this
>> to be transparent or not.
>>
>> Reading <http://www.sanog.org/resources/sanog4-kaulgud-qos-tutorial.pdf>
>> it looks like in the Diffserv terminology, it's ok to do whatever one
>> would want.
>>
>> Any feedback appreciated.
>
> Long ugly history here that I will try to avoid.
>
> IP is end-to-end and you aren't supposed to muck with the packets that are
> sent by your customers (or worse, sent by *their* customers). You don't
> know what the bits mean to their applications (unless you are one of the
> end-points of course) and screwing around with that stuff is a good way to
> make people very angry. They're not your packets--leave them alone unless
> you are being paid to do otherwise.

While it's true that IP is end-to-end, are fields such as TOS and DSCP 
meant to be end to end? A case could be argued that they are used by the 
actual forwarding devices on route in order to make QoS or even routing 
decisions, and that the end devices shouldn't actually rely on the values 
of these fields?

For example if ISPA is paying ISPX for a different amount of garenteed 
(sic) bandwidth than ISPB, how is ISPX meant to mark their traffic in such 
a way to control them seperately without using DSCP/TOS marking (assuming 
a non-MPLS network).

Also, if you are using TOS in your network to mark VoIP traffic for 
garenteed bandwidth then you're pretty much gonna have to zero it on entry 
into the network or people are going to be able to eat into your VoIP 
buckets just by setting the right TOS bits.

Seems to me that the actual meaning of TOS and DSCP is utilised on-route 
and not by the end nodes. What cause could the end nodes have to rely on 
these values?

Sam