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QoS and routers



I have a client that have VOIP on several sites over a MPLS network. In their branch offices, they have cisco 2911/2951 with some QoS configuration.

They talk to phone servers over the MPLS to a data center that have ASR 1000 routers at edge. Problem is, these ASR 1000 routers don't have any QoS config.

I know that routers don't remove the dscp tag but are they really using it if there is no qos config ?

I was under the impression that all devices along the path should have QoS config with no exception of these ASR 1000. Note that their provider do QoS on the mpls network.

What do you think ?

sorry for my english

23 Replies 23

what about this.

class-map match-any real-time 
    match dscp ef (VOIP)
    match cos 5   (VOIP)
class-map match-any foreground
    match dscp cs3 (signaling)
    match dscp af31 (signaling)
    match cos 3  (signaling)
    match dscp cs4 (video)
    match dscp cs6 (routing protocols)
    match dscp cs7 (routing protocols)
 class background
    match ??? (is this traffic less important than default ?)

policy-map Sample
 class real-time
  priority percentage 33
 class foreground
  bandwidth remaining percentage 81
 class background
  bandwidth remaining percentage 1
 class class-default
  bandwidth remaining percentage 9


policy-map SHAPE
     class class-default
          shape average 10000
          service-policy Sample

interface FastEthernet0/0
   service-policy output SHAPE

What kind of traffic do you put in background ?

I'm not sure I understand percentage. It's ratio like you explained. 1% vs 2% is the same as 10% to 20%. This I understand. But when you have several classe like this :

real-time : 33 %

foreground : 81 %

backgroud : 1%

default :9%

So foreground has 2.5x more as opposed to real-time ?

Real-time has 33x more as background ?

Default has 9x less as foreground ?

Is that it ?

What kind of traffic do you put in background ?

"Bulk" data transfers where there's no timing issue.  For example, things like backups and email exchanges (server to server).

So foreground has 2.5x more as opposed to real-time ?

Real-time has 33x more as background ?

No, real-time is LLQ, it's dequeued before all other non-LLQ traffic.  The percentage only sets an implicit policer.

Default has 9x less as foreground ?

Correct; as a ratio.  I.e. foreground will be able to obtain 90% of bandwidth compared to just default.  This assumes foreground wants all that bandwidth.  Ideally, foreground should have traffic that needs to be forwarded quickly but not actually demanding of 90% of the bandwidth.

I get it now. Thank you so much.

My last concern is about the MPLS WAN. I don't know that MPLS providers offre in term of QoS. Can I do this kind of policy all the way up to the DC ? I don't think so...

I need to call them to know what I can do.

I don't know what is the impact if my Qos policy isn't the same everywhere along the path..

Years ago, I worked with several MPLS providers.  At that time, their QoS support was "weak".  Don't know what they might offer today.

You don't have to have an identical QoS policy end-to-end, but of course when you don't, you don't obtain consistent QoS traffic treatment.  However, you sometimes are limited in what you can do.

Currently, I work in an environment where not all our equipment supports the same QoS features.  We tried to define a QoS policy that serves our needs and is LCD on most equipment, but not all if it.  Equipment that cannot support our policy have QoS configurations that support it as best they can.

Hi Joseph,

I talked to my MPLS provider and they seems to be very open to do anything that we need so I think there is a good chance that our policy and their match.

On another topic, I was wondering something.

How does an equipement manage DSCP when there is no policy-map but DSCP is trust everywhere.

I ask this because, I'm new at this company. When I ask them if they have some QoS configured inside their sites (branches offices and DC). They always say "yes DSCP is trust everwhere".

When I look at the config, yes DSCP is trust but there is absoulotely no policy-map configured on any interface along the path.

So, is there any sort of quality of service when you don't apply any policy on interface ? Do EF is prioritized ? And what about the rest of the traffic ?

I was under the impression you need to apply a policy to an interface to tell it how to class trafic , etc.