Hi All,
When using shaping and shaping queues, i ran into a behavior i didnt expect.
According to QoS exam guide, packets should only enter shaping queues
when shaping is active. If shaping is not active (packets are
conforming) it should bypass the shaping queues and go directly to
software queues and then TX-ring.
For example, defining our PARENT policy:
policy-map OVERALL
class class-default
shape average 20000
service-policy SUB-POL
And our "CHILD" policy:
policy-map SUB-POL
class ICMP
priority 10
class SSH
bandwidth 8
class TELNET
And applying the OVERALL policy outbound on an interface:
R2(config-if)#do sh run int s0/1/0
Building configuration...
Current configuration : 132 bytes
!
interface Serial0/1/0
ip address 192.168.25.2 255.255.255.0
load-interval 30
no keepalive
clock rate 128000
service-policy output OVERALL
end
I would expect my packets NOT to hit any shaping queues unless they
exceed 20kbit
Doing a ping reveals a different behavior:
R2#ping 192.168.25.5 rep 50
Type escape sequence to abort.
Sending 50, 100-byte ICMP Echos to 192.168.25.5, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!.!!!!!!!!!
Success rate is 98 percent (49/50), round-trip min/avg/max = 12/14/16 ms
R2#sh policy-map int
Serial0/1/0
Service-policy output: OVERALL
Class-map: class-default (match-any)
51 packets, 5324 bytes
30 second offered rate 3000 bps, drop rate 2000 bps
Match: any
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/1/0
(pkts output/bytes output) 50/5420
shape (average) cir 20000, bc 500, be 500
target shape rate 20000
Service-policy : SUB-POL
queue stats for all priority classes:
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/1/0
(pkts output/bytes output) 49/5096
Class-map: ICMP (match-all)
50 packets, 5000 bytes
30 second offered rate 2000 bps, drop rate 2000 bps
Match: protocol icmp
Priority: 10 kbps, burst bytes 1500, b/w exceed drops: 1
Class-map: SSH (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: protocol ssh
Queueing
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 0/0
bandwidth 8 kbps
Class-map: TELNET (match-all)
0 packets, 0 bytes
30 second offered rate 0 bps
Match: protocol telnet
Class-map: class-default (match-any)
1 packets, 324 bytes
30 second offered rate 0 bps, drop rate 0 bps
Match: any
queue limit 64 packets
(queue depth/total drops/no-buffer drops) 0/0/0
(pkts output/bytes output) 1/324
As can be seen, all packets seems to traverse the Shaping queue ICMP,
even though most of the packets (all near one according to this)
should not be shaped.
Anyone know if this is an implementation thing in IOS, that the
counters will still be updated even though they in reality bypass the
queues or if something else is going on here?
Just curious.
Sincerely,
Kim Pedersen
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