2960X: Limit overall Traffic of a Gigabit Port to 2 Mbit/s - QoS Shaping/Sharing

[Robert Singer]

Hi!

I have the following Challenge, to achieve. We got a new Wiring Closet on the Access Layer on the Campus Attached. These 3560V2 Switch is connected via a 2 Mbit/s transparent Layer 2 Line to a new 2960X Switch and from that on to the Distribution Layer VSS 6504-E.

Problem: Voice traffic from the Datacenter Site to the access site ( RTP) is dropped when the 2 Mbit/s Line is full due to other traffic.

I try to achieve the following: Since the 3560V2 Switch is connected via a 2 Mbit/s leased line to a Gigabit Port on both Sides ( 3560v2 <-2Mbit/s-> 2960X I try to limit the maximal allowed bandwidth downstream to the 3560V2 on 2 Mbit/s. The reason for that is, that I want to control, which traffic is dropped and not the Provider Equipment is dropping frames for me.

Let me illustrate that with an Diagram:

First of all, I tried to implement the following sharing and shaping configuration

2960X:

interface GigabitEthernet3/0/24
 switchport mode trunk
 bandwidth 2000
 load-interval 30
 srr-queue bandwidth share 1 45 52 7
 srr-queue bandwidth shape 10 0 0 0
 srr-queue bandwidth limit 10
 priority-queue out
 mls qos trust dscp

First of all, I thought the when the priority queue is served with shape 10 0 0 0 that means the following

1/10 = 10% for Queue 1 are reserved. Since 0 is for the other queues, the traffic is shared between this Queues based on the share command.

Since I have a Gigabit Interface, the 10% = 100 Mbit/s. I want to limit the overall traffic to 2 Mbit/s + Voice always prio ( priority-queue out )

I thought maybe I set the bandwidth parameter ( I know only for routing protocols, but I thought maybe also for Qos?) That did not worked,

also the srr-queue bandwith parameter only can limit the port to max 10% of Gig... that is 100 Mbit/s... I need 2Mbit/s....

Also, a service

  Policy Map policy-airport
      Description: Policy Map fuer Airport
    Class class-default
      police 1900000 8000 exceed-action drop

can only be bind on input interfaces, not on output interfaces. :-(

So is there any idea I can prio Voice over Data on the 2960X Trunk to the 3560V2 and limit it to 2 Mbit/s before it goes on the wire ?

Maybe this Setup work ?

interface GigabitEthernet3/0/24
 switchport mode trunk
 bandwidth 2000
 load-interval 30
 srr-queue bandwidth shape 100 200 400 400
 priority-queue out
 mls qos trust dscp

= 1/100 for Q1 = 1%

= 1/200 for Q2 = 0,5%

=1/400 for Q3 = 0,25%

= 1/400 for Q4 = 0,25%

in sum 2% in strict manner on the Gig Link allocated = 2 Mbit/s

[Joseph W. Doherty]

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Posting

I'm not 100% certain with the 2960X, but if it works like the 3560/3750 series, you'll want to run the interface physically at 10 Mbps, and then use the bandwidth limit command set to 20% or less.  (The port hardware shaper, at least on 3650/3750 isn't exact, so you may need to shape slower to stay under 2 Mbps.)  With the port shaped, you can then manage priority of your traffic.  For example, PQ for your VoIP bearer traffic.  (You'll also need to enable QoS globally, trust ingress DSCP [i.e. having trust on your egress port, alone, isn't sufficient], and insure your traffic maps to the desired queues.)

PS:

An alternate approach, would be to place an inexpensive router (e.g. 800 series) between your switches and your 2 Mbps link, as they have better QoS features.