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ASR 1001 Unexpected output drops

Hi Everyone

I have an issue with an ASR 1001. The problem occurs with MQC shaping applied to a gigabit interface in the outbound direction. The CIR of the provider we are using is 100Mb/sec, so we are shaping to that value. However when reported traffic levels are about 60Mb/sec, we see a steady increase in output drops.

Here is the relevant config;

policy-map QOS-OUT

class PREMIUM

  priority 6144

class ENHANCED-1

  bandwidth 1024

class class-default

  set dscp af11

policy-map OUT

class class-default

  shape average 100000000

  service-policy QOS-OUT

interface GigabitEthernet0/0/0

no ip address

no ip redirects

no ip proxy-arp

load-interval 30

no negotiation auto

interface GigabitEthernet0/0/0.101

bandwidth 100000

encapsulation dot1Q 101

ip address x.x.x.x x.x.x.x

no ip redirects

no ip proxy-arp

service-policy output OUT

The physical interface shows the following ( note we are using dot1q sub interfaces but only have one in use, so the stats on physical interface only relate to this one)

sh int g0/0/0

GigabitEthernet0/0/0 is up, line protocol is up

  Hardware is ASR1001, address is 649e.f329.3d80 (bia 649e.f329.3d80)

  Description:

  MTU 1500 bytes, BW 1000000 Kbit/sec, DLY 10 usec,

     reliability 255/255, txload 17/255, rxload 6/255

  Encapsulation 802.1Q Virtual LAN, Vlan ID  1., loopback not set

  Keepalive not supported

  Full Duplex, 1000Mbps, link type is force-up, media type is SX

  output flow-control is on, input flow-control is on

  ARP type: ARPA, ARP Timeout 04:00:00

  Last input 02:20:54, output 02:20:54, output hang never

  Last clearing of "show interface" counters 00:03:11

  Input queue: 0/375/0/0 (size/max/drops/flushes); Total output drops: 267

  Queueing strategy: Class-based queueing

  Output queue: 0/40 (size/max)

  30 second input rate 26851000 bits/sec, 12150 packets/sec

30 second output rate 60529000 bits/sec, 18885 packets/sec

     2330446 packets input, 709862871 bytes, 0 no buffer

     Received 10 broadcasts (0 IP multicasts)

     0 runts, 0 giants, 0 throttles

     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

     0 watchdog, 0 multicast, 0 pause input

     3541955 packets output, 1634851452 bytes, 0 underruns

The policy-map shows;

snip

    Class-map: class-default (match-any)

      3217551 packets, 1484943980 bytes

      30 second offered rate 60418000 bps, drop rate 4000 bps

      Match: any

      Queueing

      queue limit 416 packets

     (queue depth/total drops/no-buffer drops) 0/267/0

      (pkts output/bytes output) 3535758/1630202127

      shape (average) cir 100000000, bc 1000000, be 1000000

      target shape rate 100000000

I have also tried increasing the hold queue, however this does not help with the drops. Increasing the shaping rate to 200Mb/sec gets rid of almost all the drops (not quite all!) but is not what we need.

I think that we should see some drops when rates spike above 100mb, however the amount we are seeing seems excessive?

Does anyone have any views on this?

Thanks

Mike

1 REPLY

ASR 1001 Unexpected output drops

Hello

You have 267 drops, I don't see that as being excessive.

Here as example from one of device that I have

    Class-map: class-default (match-any)

          5155683605 packets, 2284544032554 bytes

          30 second offered rate 466000 bps, drop rate 4000 bps

          Match: any

          Queueing

            Output Queue: Conversation 139

            Bandwidth 55 (%)

            Bandwidth 2200 (kbps)

            (pkts matched/bytes matched) 860129821/2284338175242

        (depth/total drops/no-buffer drops) 0/801807/0

             exponential weight: 9

             mean queue depth: 0

Of course, different bandwidth (4Mbps) but this is not the point. The drops here are generate from the overload of the line of course.

How fast are the drops increase? If you have 100Mbps contracted from the provided by SLA then you should not have drops at 60Mbps. But this also depends of the contract type.

Nevertheless what I noticed from my experience, just as an FYI, is that I'm more comfortable using percentage in the classes and also add a bandwidth percent for the class-default. Just to know how much I assign for the class default.

HTH,

Calin

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