[j-nsp] Use cases for IntServ in MPLS backbones

[Mark Tinka]

On 2/Oct/18 12:31, Saku Ytti wrote:

> This is not the point here, the point is are you guaranteeing
> something with the DSCP. The point is opposite, if you can avoid
> caring or acting on them, then you do not need to change them.

The implementation is irrelevant. Whether I use DSCP, IPP, EXP or
carrier-pigeon, the end-goal is to provide some guarantees.

In this case, DSCP is a good way to provide guarantees. But even though
we cannot provide guarantees to off-net traffic, it doesn't mean we
should accept the potential issues that could occur due to the lack of a
global standard on how DSCP values should be honoured on the general
Internet.


> Me-Asia ---> Internet ---> Me-Europe
>
> I control my ends PE<=>CE, Me-Europe is often congested and I want to
> prioritise SSH interactive sessions there. I could just set SSH to EF
> in Me-Asia and have Me-Europe honour it. Internet needs just to pass
> the bits, not act on them.

In theory, the Internet needs to just pass those bits. But in practice,
can you actually expect any guarantee of that when those SSH packets are
traveling from Taipei, to Hong Kong, to Beijing, to Moscow, to Kiev, to
Frankfurt, to London, to Stockholm, and perhaps, finally, to Helsinki?


> Now of course I can configure stuff so that I break stuff by DSCP
> values. But that's not Internet's fault.

Think about it this way, LOCAL_PREF for BGP means nothing outside of
your AS.

In my mind, DSCP is just like LOCAL_PREF. We are really banging our
heads on a wall if we think we can use it effectively outside of a
walled-garden.


> Danish incumbent TDC has ran full pipe for maybe two decades. There is
> no way to guarantee what others do, but they view that it's not their
> position to mangle other people's traffic, if they can avoid it.
>
> I fully understand that some people technically cannot do short or
> full pipe, that's fine. But if you can, I think you should.

Again, it's not about the actual feature itself. It's about the lack of
a global standard on how to treat DSCP when in the global space.

TDC lives in a good world where it does not have to talk to the rest of
the Internet. But provided they have to talk to the rest of the
Internet, there is no way they can ensure consistent performance for
their customers if they allow inbound or egress Internet traffic to run
amok with whatever DSCP/IPP vlaues set outside of their control.

We learned the hard way.

Mark.