QoS and bandwidth "mismatch"

[rasmusan1]

Hi

If you on a router has a gigabit interface connected to your ISP equipment, and your actual bandwidth from ISP in only fx. 50Mbit/s - how should you correctly handle QoS configuration then.

Would it be enough to use the interface bandwidth command and define the 50Mbit/s on the gigabit interface?

Or would you have to create a parent-child service-policy, where your parent shapes the traffic to 50Mbit/s, and the child does the actual QoS policy? fx. like:

policy-map QoS-PARENT
 class class-default
 shape average 20000000
 service-policy QoS-CHILD

interface gig0
 service-policy output QoS-PARENT

thanks.

[paul driver]

Hello

It best to use Hqos shaping (like you have posted) to set your egress Committed Interface Rate (CIR) rate as the interface bandwidth command is only really used for routing protocol metric calculation such as eigrp/ospf

[rasmusan1]

Hi Paul

You say "it's best" - but is it required? would it work without using shaper? pros/cons?

Just to understand completely, as I am having a hard time finding definitive answer to this ;-)

/Rasmus

[paul driver]

Hello

---

@rasmusan1 wrote:

Hi Paul

You say "it's best" - but is it required? would it work without using shaper? pros/cons?

Just to understand completely, as I am having a hard time finding definitive answer to this ;-

---

No it isn't required but I would go as far as to say its recommended.
It will work without any shaping but then you are open to send traffic that exceeds your negotiated ISP CIR and if you do exceed this then depending on how nice your ISP is it can allow a certain amount of excess traffic then begin to drop it or it could just randomly drop it, but no doubt they will charge you for the privilege so I would say its best not to exceed your CIR in the first place.

Another example can be site-site connection where your site has an higher cir rate then your neighbor, Overtime you could overwhelm your neighboring sites connection as your sending more traffic your neighbors wan link can handle however if you shape either side this problem be could negated.

[rasmusan1]

so, lets say I have a gigabit WAN interface connected to ISP CE equipment - my WAN speed from ISP is 20mbit/s. I will not be charged anything, trying to push more than that 20mbit/s, so that is not an issue.

I have set the interface bandwidth command on my WAN interface to 20mbit/s, and applyed my service policy (see below for config example)

If traffic that falls in class-default, tries to use all bandwidth (lets say FTP upload), will my policy then handle this correctly, and make sure VoIP-Realtime traffic is sent before class-default traffic?

I'm wondering, because the GigabitEthernet0 interface is not congested....

policy-map WAN
class VoIP-Realtime
priority percent 30
class Signaling
bandwidth percent 5
class BusinessCritical
bandwidth percent 20
class class-default
fair-queue
!
interface gigabitEthernet0
bandwidth  20000

service-policy output WAN

[paul driver · Accepted solution]

Hello

The interface bandwidth has nothing to do with the actual speed you will be sending that command is only really used for routing protocol metric calculation

If you have a contract with the ISP for 20mb then shape your overall egress traffic to accommodate tha

example:

policy-map QoS-CHILD
class VoIP-Realtime
priority percent 30
class Signaling
bandwidth remaining percent 5
class BusinessCritical
bandwidth remaining percent 20
class class-default
fair-queue

policy-map QoS-PARENT
class class-default
shape average 20000000

service-policy QoS-CHILD

Note: if you don't wish to classify any traffic then just set all traffic to your contractual CIR

policy-map QoS-CHILD
class class-default
fair-queue

policy-map QoS-PARENT
class class-default
shape average 20000000
service-policy QoS-CHILD

interface gig0
service-policy output QoS-PARENT

[Georg Pauwen]

Hello,

ideally the average should be 80 to 85 percent of the max bandwidth, so the shaper gets activated before the bandwidth limit is reached:

policy-map SHAPE_50MB
class class-default
shape average 40000000

!

interface gig0
service-policy output SHAPE_50MB

[Bekzod Fakhriddinov]

It's required to shape first then use queuing and policing on that shaped bandwidth. Only this way router can properly calculate resources and do right decision.