From: simon hart (simon.hart@btinternet.com)
Date: Tue Feb 22 2005 - 17:47:46 GMT-3
Roy,
You are correct in your assumption that if an ISP does nothing with the
IPprec they receive from their clients and they have WFQ and WRED enabled on
their interfaces then you could potentially derive some benefit. However
the major assumption is that they do nothing with the IPprec.
I cannot speak for every ISP out there, however the company I work for (they
shall remain nameless for the time being) will re-mark all traffic on the
ingress Access router. However things do not stop there. Our core network
does not switch 'raw' IP packets, it uses MPLS for connectivity across our
ISP core. If we are offering 'vanilla' ISP services then there would be no
IPprec, or Diffserv to MPLS exp bit mapping. Therefore the core routers
would not have an inkling on how the IP Packets are marked.
Therefore if you were to use the ISP services of the company I work for,
then you would derive no benefit from marking your IP packets. It becomes
somewhat different if you were to subscribe to an MP-iBGP MPLS VPN - but I
guess that is another subject
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of Roy
Dempsey
Sent: 22 February 2005 18:02
To: swm@emanon.com
Cc: Cisco certification
Subject: Re: Setting IP precedence in the real world?
Thanks Scott,
Clear and informative as usual! I still have a couple of further questions.
My question was partly an attempt to question the fact that IP
precedence does more than act as a tag when used to mark traffic. You
can mark traffic and act based on that. But, unlike a tag, the
precedence value on its own has some significance, even if you don't
explicitly match the precedence. So, if I were to mark traffic leaving
my network and it wan't rewritten, I *could* achieve some benefit if
WFQ or WRED were employed by upstream routers.
I see what you mean by perception. I though that there was a general
scale to IP precedence with a higher value meaning higher priority.
Why not mark traffic with a precedence of 5? Any device configured to
look at precedence will see it. In times of congestion, it may
actually make a difference if WFQ or WRED is configured, or they've
configured the routers to treat precedence 5 as a priority.
I also understand that there is no incentive to an ISP to treat my
traffic with a higher priority, but if the above were through, it
would be possible to use the features available in QoS features like
WFQ and WRED on Cisco routers to improve the performance of traffic
without the explicit agreement of my ISP.
This really is a theoretical question, because I don't have this type
of experience to date. I am just curious about how the real world
treats precedence, as opposed to private or labbed environments.
BTW, apart from WFQ and WRED is there any other QoS feature which uses
precedence by default.
Also, Wendells QoS book seems to be out of print. Anyone know where I
can buy a copy at a reasonable price?
Thanks
Roy
On Tue, 22 Feb 2005 12:11:49 -0500, Scott Morris <swm@emanon.com> wrote:
> Not so much as rewriting them (though some do) but more of ignoring the
> implications.
>
> The problem is that QoS is end-to-end, and what motivation does any ISP
have
> to treat your traffic better than one of their other customers?
>
> They'll be happy to sell you SLAs though. And then will tell you how to
> mark it.
>
> Beyond that though, we have problems in perception. What is important to
> your network may not be to mine. What makes a "prec 3" level of
importance
> to you may not have any correlation in my world.
>
> This is where the Per Hop Bevior RFC's came in to try to give a common set
> of interpretations at any network along the way. The Assured Forwarding
> (AF) classes and Expedited Forwarding (EF) class came from there.
>
> But it still boils town to money and motivation!
>
> HTH,
>
> Scott Morris, MCSE, CCDP, CCIE4 (R&S/ISP-Dial/Security/Service Provider)
> #4713, JNCIP, CCNA-WAN Switching, CCSP, Cable Communications Specialist,
IP
> Telephony Support Specialist, IP Telephony Design Specialist, CISSP
> CCSI #21903
> swm@emanon.com
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Roy
> Dempsey
> Sent: Tuesday, February 22, 2005 11:56 AM
> To: Cisco certification
> Subject: Setting IP precedence in the real world?
>
> Hi all,
>
> I've always struggled with understanding and applying the correct QoS
> solution to a particular problem. I'm working hard at understanding when
and
> where different solutions are appropriate. As with other topics, I think I
> understand the theory, but need to understand the real-world application
> properly.
>
> While working through MQC, I couldn't help wondering about how important
ip
> precedence values are in the real world and, in particular, the Internet.
On
> private networks, I can see the value in setting the ip precedence value,
> and providing levels of service using these values.
>
> When sending traffic onto the Internet, is there any value in setting
> precedence values? Would ISPs rewrite these values as standard? Even if
ISPs
> don't explicitly use precedence values, wouldn't it be beneficial where
QoS
> devices like WRED and WFQ are employed, as these can use the precedence
> value?
>
> Thanks again,
> Roy
>
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