From: chrlewis@cisco.com
Date: Sun Sep 25 2005 - 21:53:05 GMT-3
Hi Simon,
I think you have it right and make a good point about the bandwidth
statement.
For anyone that does not want to memorize this sort of stuff for the
exam, I'd strongly recommend familiarity with the show policy-map
interface command, it verifies what pecentage has been applied. Taking
the config supplied and applying it to an interface with multiple DLCIs
on it shows the policy applied to all DLCIs and the percentage
calculated, an example is at the end of this response.
Regards adaptive shaping, this is my understanding.
Adaptive shaping using the older BECN awareness means that should the
interface see BECNs, it will start to throttle the rate it transmits at
down from CIR to mincir, but no lower. I believe the congestion
awareness option does the same thing, but uses interface congestion
rahter than BECNs as the trigger for shaping and thorttling back of
output. The throttling algorithm for interface congestion awareness is
given in the documentation as following:
When the congestion level exceeds a configured value called queue depth,
the sending rate of all PVCs is reduced to the minimum committed
information rate (minCIR). As soon as interface congestion drops below
the queue depth, the traffic-shaping mechanism changes the sending rate
of the PVCs back to the committed information rate (CIR).
So, if there is no congestion, there will be no shaping. However set
statements are not conditional upon bandwidth or priority statements
being active in order for them to mark. The class-map identifies traffic
and the policy map applies the set commands, if there is no congestion,
the bandwidth commands will not be active but the plain set commands
will be, just as if no bandwidth command was configured.
Chris
Router2(config-if)#do sh policy-map int
Serial1/0: DLCI 221 -
Service-policy output: QOS
Class-map: QOS-1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 5
Queueing
Strict Priority
Output Queue: Conversation 24
Bandwidth 30 (%)
Bandwidth 9 (kbps) Burst 225 (Bytes)
(pkts matched/bytes matched) 0/0
(total drops/bytes drops) 0/0
QoS Set
dscp ef
Packets marked 0
Class-map: QOS-3 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 1
Queueing
Output Queue: Conversation 25
Bandwidth 20 (%)
Bandwidth 6 (kbps) Max Threshold 64 (packets)
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
QoS Set
dscp af33
Packets marked 0
fr-de
Packets marked 0
Class-map: QOS-2 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 3
Queueing
Output Queue: Conversation 26
Bandwidth 30 (%)
<------------------------------------------------------percent
calculation
Bandwidth 9 (kbps) Max Threshold 64 (packets) <-------------
(pkts matched/bytes matched) 0/0
(depth/total drops/no-buffer drops) 0/0/0
QoS Set
dscp af31
Packets marked 0
Class-map: class-default (match-any)
1 packets, 88 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: any
Queueing
Flow Based Fair Queueing
Maximum Number of Hashed Queues 16
(total queued/total drops/no-buffer drops) 0/0/0
QoS Set
dscp default
Packets marked 1
Serial1/0: DLCI 244 -
Service-policy output: QOS
Class-map: QOS-1 (match-all)
0 packets, 0 bytes
5 minute offered rate 0 bps, drop rate 0 bps
Match: ip precedence 5
Queueing
Strict Priority
Output Queue: Conversation 24
Bandwidth 30 (%)
Bandwidth 9 (kbps) Burst 225 (Bytes)
(pkts matched/bytes matched) 0/0
(total drops/bytes drops) 0/0
QoS Set
dscp ef
Packets marked 0
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
simon hart
Sent: Saturday, September 24, 2005 2:39 AM
To: Dennis J. Hartmann; ccielab@groupstudy.com
Subject: RE: NMC Lab# 18 QoS Configuration
Hi Dennis,
MQC will pick up on the values assigned within Frame map class when
frame traffic shaping is enabled. In fact MQC will ignore the interface
bandwidth value assigned.
However MQC will use the value of mincir for assigning bandwidths.
Therefore in your example the bandwidth will be carved up as
30% of 32k for QOS-1
30% of 32k for QOS-2
20% of 32k for QOS-3
20% of 32k for Class-default
If no mincir figure was given within the map-class statement then MQC
would pick up on cir/2 = 125000 / 2 for the values.
Now what I am not sure on is the adaptive shaping, perhaps some others
could help.
If the interface is not congested then there will be no traffic shaping.
If there is no traffic shaping will the service policy within the Map
class be active?? If not then the CBWQ will not be working when the
interface is not congested, and thus your set statements will not work.
Would really like some clarity on this
Simon
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
Dennis J. Hartmann
Sent: 24 September 2005 04:14
To: ccielab@groupstudy.com
Subject: NMC Lab# 18 QoS Configuration
While I do NOT endorse adaptive traffic-shaping for VoIP networks of
any sort, I have come across this scenario in a CCIE practice test. The
question wants the admin to configure a Frame-Relay QoS policy that will
adapt rates based on interface congestion because the interface only
runs at 125kbps, but there are multiple PVCs terminating on the
interface. This calls for the frame-relay adaptive-shaping
interface-congestion command in the map-class.
I don't think the answer key is correct though. In the following
policy, the mapclass has the cir and mincir configured and the CBWFQ
policy is being called to carve up the bandwidth on the interface. I
don't believe that the MQC has the ability to configure a policy based
on the cir in a frame map-class. This is why we normally use nested
policies to configure frame-relay traffic-shaping and congestion
management. The adaptive traffic-shaping interface-congestion feature
is not a part of the MQC however.
Given the scenario, I believe the only logical choice would be to
put a bandwith 125 statement on the Serial 0/0 interface so the CBWFQ
congestion management policy is based on 125kbps, not the default of
1544kbps.
Comments and suggestions welcome.
interface Serial0/0
no ip address
encapsulation frame-relay
no fair-queue
frame-relay class Frame-QOS
frame-relay traffic-shaping
policy-map QOS
class QOS-1
priority percent 30
set dscp ef
class QOS-3
bandwidth percent 20
set dscp af33
set fr-de
class QOS-2
bandwidth percent 30
set dscp af31
class class-default
fair-queue
set dscp default
class-map match-all QOS-1
match ip precedence 5
class-map match-all QOS-2
match ip precedence 3
class-map match-all QOS-3
match ip precedence 1
map-class frame-relay Frame-QOS
frame-relay cir 125000
frame-relay mincir 32000
frame-relay adaptive-shaping interface-congestion service-policy
output QOS
Sincerely,
Dennis J. Hartmann
White Pine Communications
CCSI#23402 / CCVP / CCIP / CCNP
Cisco Optical, VPN & IDS Specialist
MCSE
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