WAN Ingress Policer packet drops

[sms999001]

Hello,

I would appreciate a "second opinion" whether the WAN ingress Parent Policy below will drop packets regardless if they are High Priority pkts (eg/ EF, AF41) or if they are best effort (DSCP 0) packets.

I have included a 'show policy-map interface' output which shows the Parent Policy dropping packets

I have attached the Child policy as well but my query is mainly focussed on the Parent Policy. The ios is version 15.1(4)M3 and the router is a 2911.

The background is that we having Video packet loss which is affecting the picture quality.

---

policy-map 20Mb_WAN_Parent_In
 class class-default
  police cir 20480000 bc 3840000 be 7680000
   conform-action transmit
   exceed-action drop
  service-policy 20Mb_WAN_Child_In

show policy-map interface
 GigabitEthernet0/0.1897

  Service-policy input: 20Mb_WAN_Parent_In

    Class-map: class-default (match-any)
      177963787 packets, 104965314158 bytes
      30 second offered rate 965000 bps, drop rate 0 bps
      Match: any
      police:
          cir 20480000 bps, bc 3840000 bytes, be 7680000 bytes
        conformed 177961960 packets, 104963180269 bytes; actions:
          transmit
        exceeded 1828 packets, 2133953 bytes; actions:
          drop
        violated 0 packets, 0 bytes; actions:
          drop
        conformed 965000 bps, exceed 0 bps, violate 0 bps
-------

Thanks in advance

S

[luismorales31 · Accepted solution]

Hello,

Yes, as I understand the Parent policer can drop any tipe of traffic (regardless of it's DSCP value). In this link (http://www.cisco.com/c/en/us/td/docs/routers/10000/10008/configuration/guides/qos/qoscf/10qhier.html#wp1041745) this behaviour is explained:

RRestrictions and Limitations for Hierarchical Input Policing Policies

•Packet classification for the bottom-level child policy map occurs before the top-level policer acts on the traffic classes.

•Traffic policing at the top-level parent does not guarantee fairness in sharing bandwidth among the child classes. If packets from two different traffic classes arrive at the same rate and then go through a traffic policer, the output rates of the two classes might be different because the hierarchical input policer acts as an aggregate policer. The parent policer might drop packets in one class in favor of the other class. This situation can happen when the top-level policer has enough tokens when the packets for one class arrive, but does not have enough tokens left for the other class. Based on the arrival pattern of the packets, this pattern could continue indefinitely.

Basically, the Parent Policer acts on the aggregate traffic it receives from the child class, without any regards to the DSCP value.

You can see some information about this for your IOS Version in the following link (it referes to three-level hierarchy, but the same should apply to a two-level hierarchy): http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/qos_plcshp/configuration/15-mt/qos-plcshp-15-mt-book/qos-plcshp-mod-cli-tlhp.html

Regards,

Luis

[sms999001]

Hi Luis,

Thank you very much for answering my question. That's very helpful and I can use it to report back to my managers.

regards

Suresh

[luismorales31]

Hello Suresh,

I'm glad I could help.

Regards,

Luis