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QoS and routers

Vinny
Beginner
Beginner

Hi,

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

2 Accepted Solutions

Accepted Solutions

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

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

Correct, by default routers don't change the ToS, but also by default, they generally don't do any QoS (unless configured to do so).

I was under the impression that all devices along the path should have QoS config with no exception of these ASR 1000

QoS is generally only needed where there's congestion adverse to the service needs of the application, and where QoS can mitigate.  However, as adverse congestion can "sneak up" on you, is one reason the "book" advocates it be configured end-to-end.

Note that their provider do QoS on the mpls network.

It's been a while since I've worked with MPLS service providers' QoS, but when I did, often it was a "weak" implementation (often sort of the QoS support you might find on a switch).

View solution in original post

Not sure what the priority bandwidth allocation is when not specified.

#1 As a general rule, bandwidth reservation guarantee that bandwidth to a class, but do not hold it when it's not used.  Priority class bandwidth settings also generally set an implicit policer that can limit that class to the amount of bandwidth specified, but again, unused bandwidth is available to other classes.

#2 No, placing one class above another doesn't make it more important, but classes are matched in the sequence listed.  I.e. if more than one class matches a particular kind of traffic, the traffic will use the first class it matches.

View solution in original post

23 Replies 23

Joseph W. Doherty
Hall of Fame Master Hall of Fame Master
Hall of Fame Master

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

Correct, by default routers don't change the ToS, but also by default, they generally don't do any QoS (unless configured to do so).

I was under the impression that all devices along the path should have QoS config with no exception of these ASR 1000

QoS is generally only needed where there's congestion adverse to the service needs of the application, and where QoS can mitigate.  However, as adverse congestion can "sneak up" on you, is one reason the "book" advocates it be configured end-to-end.

Note that their provider do QoS on the mpls network.

It's been a while since I've worked with MPLS service providers' QoS, but when I did, often it was a "weak" implementation (often sort of the QoS support you might find on a switch).

thanks for this complete anwser !

Hi have some more questions about QoS.

Let's say I have an output policy-map that looks like this :


    
policy-map Output-Policy
    class Output-Media-VOIP
        priority
    class Output-Signal-VOIP
        bandwidth remaining percent 5
    class Output-Control-Mgmt
        bandwidth remaining percent 5
    class class-default

1- As you can see, voice data is set as priority (30% default I think?). Does that mean that 30 % of the bandwidth is ALWAYS reserved for voice ? When there is no congestion and voice data use, let's say 5 %, can other queues use the bandwidth left or priority queue is fixed and cannot be shared ?

2- Does the order is important. In that example, Signaling is above Control protocols. Does this makes signal more important ? If I have ato add new classes, should I review my order before adding them or I can just add them as I want ?

thanks !