From: simon hart (simon.hart@btinternet.com)
Date: Fri Apr 15 2005 - 17:47:31 GMT-3
I believe that the two configurations are quite different,
The first is using an access list. An access list is evaluated step by step
until a condition is met, therefore:
If a packet has a dscp marking of 45 it is going to be classed in the class
map and appropriate policy taken
If a packet has precedence of 7 it is going to be classed in the class map
and appropriate policy taken
If the packet has neither it will not be classified in this classs.
Now the second statement says:
If it is prec 7 and not dscp 45 then it will not be classified. If it is
dscp 45 and not 7 it will not be classified.
If it is both prec 7 and dscp 45 it will be classified.
This means that no packet will ever match the second configuration for the
reasons outlined by Bob. A packet cannot be prec 7 at the same time as dscp
45. No traffic in the second config will ever be classified, whilst traffic
in the first config maybe.
Now if the class map was a match any class map the resulting action would be
the same.
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of Bob
Sinclair
Sent: 15 April 2005 16:31
To: James Matrisciano; ccielab@groupstudy.com
Subject: Re: Building the Class-Map
Hi Jim,
It seems to me that the direct "match ip ..." is simpler than the extra step
with the access-list. However, wouldn't both necessarily result in a "no
match"? Your class-map is "match-all", but is it possible for one packet
to
be marked both precedence 7 and DSCP 45?
Precedence 7 is 111000 in the first 6 bits of TOS byte
DSCP 45 is 101101 in the first 6 bits of TOS byte
HTH,
Bob Sinclair
CCIE #10427, CCSI 30427, CISSP
www.netmasterclass.net
----- Original Message -----
From: James Matrisciano
To: ccielab@groupstudy.com
Sent: Friday, April 15, 2005 11:13 AM
Subject: Building the Class-Map
Question to any QoS Gurus out there. While working in the various labs
in preparation for my (next) Lab attempt, I see different ways of
building qos policies to match on DSCP values and Precedence values.
Below are two separate class-maps that to me do the same thing. Would
anyone disagree with this and if so, why? I want to be able to produce
a best practice solution in the lab, however, I want to do it the
quickest way possible. To me, simple match commands in the class-map
seem to work a lot quicker than building an extended access list, then
applying that list into the class-map. Comments?
class-map match-all with_access_list
match access-group name qos
ip access-list extended qos
permit ip any any dscp 45
permit ip any any precedence network
class-map match-all qos
match ip precedence 7
match ip dscp 45
!
jm
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