[c-nsp] Question about CBWFQ and PING times

[Andy Saykao]

Hi Peter,

Much appreciate your help with understanding QoS a little better.

---

I tried to create a Heirarchical QoS policy on a spare 7606 we have here
and no go. Tried to create a parent shaper and policer and neither
worked when the service-policy was applied to the interface.

With parent shaper:

POP2(config-if)#service-policy output POP2-POP2-PRI-PARENT-POLICY
shape average command is not supported for this interface
Configuration failed!

With parent policer:

POP2(config-if)#service-policy output MEL-TAS-PRI-PARENT-POLICY
Hierarchical policymap is not supported for this interface.
Configuration failed!

---

You wrote - "You need to tell the router that it only has 200 mbps and
not the full 1 Gbps. Otherwise it will allocate ~50 mbps (your
5%) for priority traffic and ~950 mbps for class-default."

This statement may be true but when I do a "show policy-map interface"
command, it seems to allocate the percentage of bandwidth correctly as
to what I've specified with the "bandwidth" interface command (ie:
bandwidth 5% (10000 kbps)). I read somewhere that the QoS policy takes
into account what you set the "bandwidth" interface command to. This
seems to be true when I do a "show policy-map interface" because it's
using the "bandwidth" interface command to allocate the bandwidth as
shown below.

Eg:

POP2#sh run int g4/0/2

interface GigabitEthernet4/0/2
 description POP2 to POP1
 bandwidth 200000
 ip address 203.17.96.x 255.255.255.252
 load-interval 30
 negotiation auto
 mpls ip
 service-policy output POP2-POP1-QOS-POLICY

POP2#sh policy-map int g4/0/2

 GigabitEthernet4/0/2

  Service-policy output: POP2-POP1-QOS-POLICY

  Counters last updated 00:00:00 ago

    Class-map: POP2-POP1-PRIORITY-CLASS (match-all)
      257210114 packets, 100115814069 bytes
      30 second offered rate 714000 bps, drop rate 0 bps
      Match: access-group name POP2-POP1-PRIORITY-ACL
      Queueing
      queue limit 2500 packets
      (queue depth/total drops/no-buffer drops) 0/0/0
      (pkts output/bytes output) 257210496/100115335835

      bandwidth 5% (10000 kbps)

    Class-map: class-default (match-any)
      17135073305 packets, 13449181375380 bytes
      30 second offered rate 118450000 bps, drop rate 0 bps
      Match: any

      queue limit 47500 packets
      (queue depth/total drops/no-buffer drops) 0/0/0
      (pkts output/bytes output) 17135119901/13449209630832

        Exp-weight-constant: 9 (1/512)
        Mean queue depth: 1 packets

---

So will issuing the "bandwidth" interface command allow the scheduler to
issue the correct bandwidth requirements for each class? Or does the
fact that it's a GigE interface mean that the buffers never become
exhausted and in theory no congestion will take place, so the
"bandwidth" interface command (eventhough set) plays no real part ???

Thanks.

--

Regards,
 
Andy Saykao
Systems Administrator
Netspace Online Systems Pty Ltd
Phone : 03 9811 0049
Mobile : 0401 422 406
Fax     : 03 9811 0044
E-Mail : andy.saykao at staff.netspace.net.au

-----Original Message-----
From: Peter Rathlev [mailto:peter at rathlev.dk] 
Sent: Wednesday, 25 March 2009 11:47 PM
To: Andy Saykao
Cc: cisco-nsp at puck.nether.net
Subject: RE: [c-nsp] Question about CBWFQ and PING times

On Wed, 2009-03-25 at 13:17 +1100, Andy Saykao wrote:
> POP1 = Cisco 7204VXR (NPE-G1) GigE Interface running 12.2(31)SB13
> 
> POP2 = Cisco 7606 with 4-subslot SPA Interface (7600-SIP-400) running
> 12.2(33)SRB3
> 
> 1/ "If you have a 200mbps connection going out from 
> GigabitEthernet-link your prioritising won't take effect, since
buffers will never saturate."
> So if we were to prioritize something like Voice, we would need to 
> implement some Heirarchical QoS solution on the Cisco 7606???

Generally speaking: Yes. When the scheduler needs to figure out if there
is bandwidth enough for non-priority traffic it needs to know how much
bandwidth is available. You need to tell the router that it only has 200
mbps and not the full 1 Gbps. Otherwise it will allocate ~50 mbps (your
5%) for priority traffic and ~950 mbps for class-default.

AFAIK both the SIP-400 and the G1 should be able to shape an interface
this way, but I could be wrong. :-)

> 2/ I understand your arguments exactly about not prioritizing ICMP 
> traffic, but I was told to look into this. I guess based on 1/ above, 
> some form of Heirarchical QoS solution is needed for this also.

Yes, you just need to wrap a shaping parent policy around your existing
"POP2-POP1-QOS-POLICY" policy.

Regards,
Peter



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