From: Pavel Bykov (slidersv@gmail.com)
Date: Sun Feb 15 2009 - 19:58:43 ARST
1. It's not only the technical difference of bits, it's how we interpret and
use those bits as well. What they should be used for, how where and so on.
Officially it's called an "Architecture" and is defined here:
http://tools.ietf.org/html/rfc2475
2. We prefer DSCP because they are part of new DiffServ/EF architecture, are
much more granular and backward compatible.
3. But that we most of the time mean when standard IP header does not
follow. It can be IPX but it can also be IP packet that is behind QinQ as
well, or IP behind MPLS. So not really ehtertype, but "readable/nonreadable"
IPv4/IPv6 header at the standard location
4. NEVER. We are alsways sceptical about the customer. There are exceptions
of course, where contractual agreements or VIP relations dictate otherwise.
But default is "NEVER". Used markings are usually engineered conceptually as
well as technology-dependant on backbone HW. That can get quite tricky.
5. This is how switch's hardware is engineered. I presume you're talking
about "Internal DSCP", therefore we can safely ignore trusts, policies, etc.
Switch has to make a logical decision, therefore all values have to be
quantified (have meaning) somehow. Because DSCP is most granular out of all
legal methods, DSCP is used.
6. All logical here, no tricks. That means that if you have ACL used for QoS
and you deny something, the packet will not get dropped, but some QoS action
will not be performed. If you apply that same ACL as "ip acces-group", it
will function as expected. So ACLs deny and permit as usuall, but not
pertaining to the dropping/sending but pertaining to "performing/not
performing QoS action".
7. Hierarchy is simply multi-leve in this case. Most commond example is have
Policy map with class, and within that class to have another policy map with
another class. Therefore you have policy map within policy map. That is
Hierarchical. Here are logical conceptual examples (they will look a
differently in config, but logically they can look like this)
Non-Hierarchical Example:
policy-map NONH
class voice
set ip dscp ef
Hierarchical Example:
policy-map HIER
class class-default
shape average 128000
service-policy NONH
class voice
set ip dscp ef
3-level Hierarchical Example:
policy-map MAIN
class class-default
bandwith remaing ration 1
policy-map HIER
class class-default
shape average 128000
service-policy NONH
class voice
set ip dscp ef
On Sun, Feb 15, 2009 at 2:03 AM, Raghav Bhargava <raghavbhargava12@gmail.com
> wrote:
> Hi Experts,
>
> I have some queries related to QOS which are as follows:-
>
> 1. what is the other difference between IP Precedence and DSCP apart
> from 3 bits and 6 bits in the TOS
> Byte ?
> 2. Who do we prefer over each and why?
> 3. When we say non-ip traffic , it is the protocols like decnet,
> etype-iv etc etc?
> 4. From an ISP's perspective do we always trust the markings which are
> marked by the customer on there
> packet to us ? Also what about MPLS Experimental bit and MPLS
> provider? Does a MPLS provider also
> trust the markings, if yes does he charges extra money for that service?
> 5. For every marking that a switch port receives , for example if it
> receives a Frame with a COS value
> then it will map the COS value to DSCP Value for forwarding the
> packet? My confusion is why does it
> only maps to DSCP and not IP Precedence?
> 6. I was going through the DOC CD for 3560 QOS which had this
> statement "In the QoS context, the permit and deny actions in the
> access control entries (ACEs) have different meanings than with
> security ACLs " . Is it true that ACE's work differently in QOS
> than what they usually do?
> 7. What are hierarchical and non-hierarchical policy maps?
>
>
>
>
> --
> Warm Regards
> Raghav
>
>
> Blogs and organic groups at http://www.ccie.net
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
>
>
>
>
>
>
-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sun Mar 01 2009 - 09:44:11 ARST