From: Antonio Soares (amsoares@netcabo.pt)
Date: Wed Jul 11 2007 - 20:58:28 ART
The class-default is like any other class with one exception: you cannot
change the match clause. And if you don't configure anything under the
class, the traffic will have FIFO treatment.
++++++++++++++++++++++++++++++++++
R6#conf t
R6(config)#class-map class-default
% class-default is a well-known class and is not configurable under
class-map
R6(config)#
R6(config)#policy-map qos
R6(config)#int f0/0
R6(config-if)#service-policy output qos
R6(config-if)#end
R6#
++++++++++++++++++++++++++++++++++
R6#sh policy-map int
FastEthernet0/0
Service-policy output: qos
Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
++++++++++++++++++++++++++++++++++
R6#conf t
R6(config)#policy-map qos
R6(config-pmap)#class class-default
R6(config-pmap-c)#fair
R6(config-pmap-c)#do sh policy-map int
FastEthernet0/0
Service-policy output: qos
Class-map: class-default (match-any)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 256
(total queued/total drops/no-buffer drops) 0/0/0
R6(config-pmap-c)#
++++++++++++++++++++++++++++++++++
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Jason Guy (jguy)
Sent: quarta-feira, 11 de Julho de 2007 20:03
To: ccielab@groupstudy.com
Subject: Class-default contradiction
I have been studying QoS some more, and I think the documentation
contradicts itself in relation to the class class-default. In the
Congestion management overview, it say this:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt2/qcfconmg.htm#wp1001203
CBWFQ Bandwidth Allocation
The sum of all bandwidth allocation on an interface cannot exceed 75 percent
of the total available interface bandwidth. The remaining 25 percent is used
for other overhead, including Layer 2 overhead, routing traffic, and
best-effort traffic. ***Bandwidth for the CBWFQ class-default class, for
instance, is taken from the remaining 25
percent.*** However, under aggressive circumstances in which you want to
configure more than 75 percent of the interface bandwidth to classes, you
can override the 75 percent maximum sum allocated to all classes or flows
using the max-reserved-bandwidth command. If you want to override the
default 75 percent, exercise caution and ensure that you allow enough
remaining bandwidth to support best-effort and control traffic, and Layer 2
overhead.
Then as I read through the WFQ configuration guide, it says this:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122cgcr/
fqos_c/fqcprt2/qcfwfq.htm#wp1017373
Configuring the Class-Default Class Policy The class-default class is used
to classify traffic that does not fall into one of the defined classes. Even
though the class-default class is predefined when you create the policy map,
you still have to configure it. ***If a default class is not configured,
then traffic that does not match any of the configured classes is given
best-effort treatment, which means that the network will deliver the traffic
if it can, without any assurance of reliability, delay prevention, or
throughput.***
The interesting thing is that in one paragraph it basically says 25% of
the interface is reserved (by default) for the class-default, L2, and
control. Then the other says class-default is best effort. I would
consider best-effort traffic to have to contend with the other Queue's
for bandwidth. In this case, it seems the class-default is not in
contention for the reservable 75% of the interface bandwidth (by
default).
Am I misinterpreting this? If you change the max-reserved-bandwidth to
95%, does this mean any traffic not classified has to contend for 5% of
the control traffic? What if you put a bandwidth statement under the
class-default class? Does that affect where it allocates it's bandwidth
from? Seems like the class-default should be treated like any other
class.
Jason
This archive was generated by hypermail 2.1.4 : Sat Aug 18 2007 - 08:17:40 ART