CBWFQ behavior change - 12.4 Mainline vs 12.4T (124-24.T1)

Hi group,

 There is a significant difference in CBWFQ based QoS on 12.4 and 12.4T

In 12.4T (24), CBWFQ behaves as if it has an inbuilt policer for the
reserved BW. The reserved flow stays within the reserved bandwidth during
congestion. Other flow get their share out of the remaining bandwidth.

In 12.4 Mainline and before, the reserved flow eats up all the bandwidth
based on the higher weight. Other flows don't get enough bandwidth at all.
(ofc shaping can be manually configured to restrict the CBFWQ flows).

has something officially changed? I couldn't find any explicit documentation
stating this difference.

 
Details:
-----------
 
E.g.

Out pipe = 10Mbps
In traffic-:
1. UDP1000 with CBWFQ reserved BW=6000kbps received at the rate of 8MBps on
router LAN on fa0/0
2. UDP1001 received at 20Mbps on router LAN on fa0/0

Topology-
------Clients-
--100Mbps----(fa0/0)--LAN-router-----(fa0/1)-----10mbps-------(fa0/1)----WAN
-router----

 
In 12.4T,

WAN#sh policy-map int fa0/1

 FastEthernet0/1
  Service-policy input: PM_QOS_STATS

    Class-map: CM_UDP1000 (match-all)
      226396 packets, 281183832 bytes
      30 second offered rate 5945000 bps ----> CBWFQ gets 6Mbps even when
sending at 8Mbps. The excess BW is auto-policed like it happens in LLQ.

      Match: access-group 100

    Class-map: CM_UDP1001 (match-all)
      146264 packets, 181659888 bytes
      30 second offered rate 3864000 bps -> other flow gets remaining 4MBps
(approx)
      Match: access-group 101

In 12.4 Mainline,

WAN#sh policy-map int fa0/1
 FastEthernet0/1

  Service-policy input: PM_QOS_STATS
    Class-map: CM_UDP1000 (match-all)
      1185545 packets, 1472446890 bytes
      30 second offered rate 8161000 bps ----> CBWFQ gets 8.0Mbps when
sending at 8Mbps based of the higher weight

      Match: access-group 100

     Class-map: CM_UDP1001 (match-all)
      373738 packets, 464182596 bytes
      30 second offered rate 1649000 bps-> other flow get only around 2 Mbps
      Match: access-group 101

 Configs:
 --------------
WAN-RTR
WAN#sh run policy-map
Building configuration...

 Current configuration : 142 bytes
!
policy-map PM_QOS_STATS
 class CM_UDP1000
 class CM_UDP1001
 class CM_UDP1002
 class CM_UDP1005
 class CM_UDP1004
 class CM_UDP1003
!
end

WAN#sh run int fa0/1
Building configuration...
Current configuration : 164 bytes
!
interface FastEthernet0/1
 ip address 192.168.58.2 255.255.255.0
 load-interval 30
 duplex auto
 speed 10
 no keepalive
 service-policy input PM_QOS_STATS
end

 
LAN-RTR
------------
 
LAN#sh run int fa0/1

Building configuration...
Current configuration : 202 bytes
!
interface FastEthernet0/1
 bandwidth 10000
 ip address 192.168.58.1 255.255.255.0
 load-interval 30
 duplex auto
 speed 10
 no keepalive
 max-reserved-bandwidth 100
 service-policy output PM_QOS
end

 
LAN#sh run policy-map

Building configuration...
Current configuration : 313 bytes
!
policy-map PM_QOS
 class CM_UDP1000
  bandwidth 6000
 class CM_TELNET
  priority 100

 
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Received on Sun Aug 09 2009 - 23:24:49 ART