QoS techniques:

Answered Question
Jan 28th, 2010

I have a Cisco 3560 G with the enhanced image for the CORE and HP Procurve POE for the access layer.

I’m looking to enable QoS on one port or VLAN interface that connects to the Metro Ethernet link.

This Metro E link connects to our data-center where the Voice Gateway is hosted.

The high-level topology:

CoreL3Switch01 (3560) – used to connect access layer user HP Procurve POE switches used for VOIP phones and workstations.

CoreL3Switch01 (3560) – connects to data-center over a metro E 50 Mbps link used only for networking, and network devices only.

Data network is 192.168.0.0/23

Voice network is 192.168.2.0/23

Voice and data traffic will travel to the Data-center over the 50 Mbps Metro E link which get saturated during peak hours and sporadically.

I would like to implement a QoS technique that would give priority to the voice traffic always at all times.

I do not have a lot of experience with Qos and from what I have read there are different approaches to implementing Qos.

Can someone provide some direction on the best approach to implementing a QoS profile on the Cisco switchport, or vlan interface that forwards traffic to the data-center over the metro E link?

Also Cisco links to documentation would be helpful so I can further study the approach while I implement it in production.

Thanks

Juan

I have this problem too.
0 votes
Correct Answer by sachinraja about 6 years 10 months ago

Hi Juan

Thanks for your response..

So ,if i understand right, you have a 3560, connecting to your HP procurve edge switches ? Is this a layer 2 connection ?

based on your inputs, with 123 phones you would have a max of 1 Mb traffic for your voice (considering 100 % concurrency).. i see you have a 50 MB metro link.. hence i think we should first concentrate on priritizing the traffic and not worry about policing now..  again, you can start with basic qos configurations, just concentrating on voice traffic, and add data traffic at a later point of time.. even with data traffic, we need to classify them based on their usage and criticality, - on one of the AF queues, AF31, AF21, AF 11 etc...

One important question here is, - does the IP phone tag EF automatically to the switches ? most of the phones do, but you need to check this with your vendor.. If yes, you can just do "mls qos trust" on the interfaces connecting the HP Procurve.. again, you need to check with HP if they will pass the DSCP values to the upstream switches, and not reset it.. because if HP switch resets the DSCP value, i dont think we can implement qos here... very important point here is "QOS DIFFSERVE IS END - TO -END".. so we need to take care of each component through which the traffic passes...

Incase your ip telephony vendor does not support automatic DSCP values, you need to force DSCP values on your primary 3560, by classifying the traffic and marking it on the edge... you can configure an ACL - for traffic from voice vlan, and mark the traffic as DSCP EF.. as given in the following URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_se/configuration/guide/swqos.html#wp1032145

If HP switch passes the DSCP values, your 3560 will trust the DSCP and carry EF for the voice traffic, and CS3 for signalling.. again, on the outbound 3560 switch where the metro link terminates, you can just trust the DSCP values to make sure voice traffic is prioritized..

One more question - do you have control of the network on the other side of metro link ? If not, again, your qos configuration will be unidirectional, and will not be that effective !

Hope this helps.. all the best..


Raj

Correct Answer by Pavel Bykov about 6 years 10 months ago

Hi.

QoS on 3560G is actually very flexible. The only limitations are 4 queues and 3 thresholds on output. But it actually supports hierarchical shaping.

You can apply this technique to prioritize your voice traffic:

interface LINK TO METRO

! step one is to improve shaping granularity. If the interface is already 100Mbps, then you don't have to type these commands.

speed 100

duplex full

!step to is to set the shaper to 50% of interface

srr-queue bandwidth limit 50

!next is to enable priority queue

priority-queue out

After that, you need to make sure mapping is ok. That could take some time, but you can get a hang of it.

There are much much more settings available, including hierarchical shaping, as I alaready mentioned, but simply to create a 50Meg pipe with a priority queue this should be enough.

What you shouldn't forget is to have a queue for System traffic as well. By default it is mapped to Queue 2 thresholds 3 and 4.

So these commands are good to start with:

mls qos srr-queue output dscp-map queue 1 threshold 3 40 46

mls qos srr-queue output cos-map queue 1 threshold 3 5

mls qos srr-queue output dscp-map queue 3 threshold 1 0

mls qos srr-queue output cos-map queue 3 threshold 1 0

Then make sure qos is on:

mls qos

and that all voice ports are trusted/or set with proper DSCP. For example for ports with IP Phones attached do the following:

mls qos trust device cisco-phone
mls qos trust cos

Finally, here is a guide with examples:

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_tech_note09186a0080883f9e.shtml

Please rate if helps.

Correct Answer by sachinraja about 6 years 10 months ago

Hi Juan

Before we design QOS, we normally collect all important data like:

1) how many IP phones are in use on the edge site ? Will the metro link carry only the voice signalling traffic or also the RTP traffic used for voice communication..

2) Depending on the volume of ip phones, you can appx tabulate the bandwidth which would be required on the WAN link (say 8-12kbps per session for voice g729, higher for g711 etc)

3) wht are the other data traffic which would need prioritization ? You can probably list out the applications and tabulate it with an appx .. we should also confirm if we need policing for data traffic....

4) with QOS we do 2 things - 1 ) prioritization with DSCP values, and 2) policing - restricting appropriate bandwidth.. since we would look at diffserve, we should make sure all devices on the path, from site 1 to site 2 supports dscp marking or trust..

5) also find from the voip vendor if the ip phones, signalling etc produce default DSCP values from the end points.. cisco devices do send dscp values which just needs to be trusted on the edge switches

6) On the edge switches , we would think of configuring something like Auto-QOS (3560 supports). this is just one simple command which will automatically configure all qos parameters for giving preference for voip data... you can have more info for auto-qos in the below URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_40_se/configuration/guide/swqos.html#wp1231112

7) Next we need to select an appropriate qos model for the core.. mostly with voice on, we would look at LLQ.. you need to know more on DSCP values and carrying the values from one end to another.. you would need to define class maps and policy maps based on your voice traffic and DSCP Values.. The following URL gives you more insight of sample configs for VOIP:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094660.shtml#topic1

QOS design is a big topic by itself and could have multiple levels of discussion.. it can directly enhance or impact your application performance over WAN..so make sure you understand your applications 200%...

Hope this helps.. all the best

raj

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Overall Rating: 5 (4 ratings)
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Edison Ortiz Thu, 01/28/2010 - 14:10

QoS is somewhat limited on the 3560G switch as this switch is designated as an access layer switch, not a distribution nor WAN layer switch.

You can mark the Voice traffic from the phone itself or at the ingress switchport with DSCP 46 / EF and trust the QoS marking on all switches end-to-end.

Enabling priority-queue out on all switchports end-to-end at the 3560G will enable priority queueing for DSCP46 / EF.

You can check the following documentation:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_52_se/configuration/guide/swqos.html

http://www.cisco.com/en/US/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoSDesign.html

Regards

Edison

Correct Answer
sachinraja Thu, 01/28/2010 - 14:14

Hi Juan

Before we design QOS, we normally collect all important data like:

1) how many IP phones are in use on the edge site ? Will the metro link carry only the voice signalling traffic or also the RTP traffic used for voice communication..

2) Depending on the volume of ip phones, you can appx tabulate the bandwidth which would be required on the WAN link (say 8-12kbps per session for voice g729, higher for g711 etc)

3) wht are the other data traffic which would need prioritization ? You can probably list out the applications and tabulate it with an appx .. we should also confirm if we need policing for data traffic....

4) with QOS we do 2 things - 1 ) prioritization with DSCP values, and 2) policing - restricting appropriate bandwidth.. since we would look at diffserve, we should make sure all devices on the path, from site 1 to site 2 supports dscp marking or trust..

5) also find from the voip vendor if the ip phones, signalling etc produce default DSCP values from the end points.. cisco devices do send dscp values which just needs to be trusted on the edge switches

6) On the edge switches , we would think of configuring something like Auto-QOS (3560 supports). this is just one simple command which will automatically configure all qos parameters for giving preference for voip data... you can have more info for auto-qos in the below URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_40_se/configuration/guide/swqos.html#wp1231112

7) Next we need to select an appropriate qos model for the core.. mostly with voice on, we would look at LLQ.. you need to know more on DSCP values and carrying the values from one end to another.. you would need to define class maps and policy maps based on your voice traffic and DSCP Values.. The following URL gives you more insight of sample configs for VOIP:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a0080094660.shtml#topic1

QOS design is a big topic by itself and could have multiple levels of discussion.. it can directly enhance or impact your application performance over WAN..so make sure you understand your applications 200%...

Hope this helps.. all the best

raj

juan-ruiz Fri, 01/29/2010 - 07:01

Raj,

Thanks again for your kind reply and great high-level overview.

I have been able to take your approach and gather some data on the questions you have.

I will read the links and if you can review my answers maybe I can closer to a solution.

Question 1. 123 phones and RTP will be used too

Question 3. Normal day to day traffic like file servers, email, and so on that does not need to have priority just voice.

Question 4. All phone traffic will be tagged with a diffsrv value of 43 ef

Question 5. Mitel is the vendor, the edge switches are HP Procurve, and the core switch is a layer3 3650 G with the enhanced imagine

Question 6. The edge is HP and it does not support auto qos to the best of my knowledge that is why I want to configure QoS on the Layer 3 Core switch Cisco 3560.

Correct Answer
Pavel Bykov Fri, 01/29/2010 - 02:39

Hi.

QoS on 3560G is actually very flexible. The only limitations are 4 queues and 3 thresholds on output. But it actually supports hierarchical shaping.

You can apply this technique to prioritize your voice traffic:

interface LINK TO METRO

! step one is to improve shaping granularity. If the interface is already 100Mbps, then you don't have to type these commands.

speed 100

duplex full

!step to is to set the shaper to 50% of interface

srr-queue bandwidth limit 50

!next is to enable priority queue

priority-queue out

After that, you need to make sure mapping is ok. That could take some time, but you can get a hang of it.

There are much much more settings available, including hierarchical shaping, as I alaready mentioned, but simply to create a 50Meg pipe with a priority queue this should be enough.

What you shouldn't forget is to have a queue for System traffic as well. By default it is mapped to Queue 2 thresholds 3 and 4.

So these commands are good to start with:

mls qos srr-queue output dscp-map queue 1 threshold 3 40 46

mls qos srr-queue output cos-map queue 1 threshold 3 5

mls qos srr-queue output dscp-map queue 3 threshold 1 0

mls qos srr-queue output cos-map queue 3 threshold 1 0

Then make sure qos is on:

mls qos

and that all voice ports are trusted/or set with proper DSCP. For example for ports with IP Phones attached do the following:

mls qos trust device cisco-phone
mls qos trust cos

Finally, here is a guide with examples:

http://www.cisco.com/en/US/products/hw/switches/ps5023/products_tech_note09186a0080883f9e.shtml

Please rate if helps.

juan-ruiz Fri, 01/29/2010 - 07:05

Hi this helps a lot and it the information on here is a good start for me.

I gathered more data and if you can review and let me if your approach still works.

Question 1. 123 phones and RTP will be used too

Question 3. Normal day to day traffic like file servers, email, and so on that does not need to have priority

Question 4. All phone traffic will be tagged with a diffsrv value of 43 ef

Question 5. Mitel is the vendor, the edge switches are HP Procurve, and the core switch is a layer3 3650 G with the enhanced imagine

Question 6. The edge is HP and it does not support auto qos to the best of my knowledge that is why I want to configure QoS on the Layer 3 Core switch Cisco 3560.

Correct Answer
sachinraja Fri, 01/29/2010 - 07:17

Hi Juan

Thanks for your response..

So ,if i understand right, you have a 3560, connecting to your HP procurve edge switches ? Is this a layer 2 connection ?

based on your inputs, with 123 phones you would have a max of 1 Mb traffic for your voice (considering 100 % concurrency).. i see you have a 50 MB metro link.. hence i think we should first concentrate on priritizing the traffic and not worry about policing now..  again, you can start with basic qos configurations, just concentrating on voice traffic, and add data traffic at a later point of time.. even with data traffic, we need to classify them based on their usage and criticality, - on one of the AF queues, AF31, AF21, AF 11 etc...

One important question here is, - does the IP phone tag EF automatically to the switches ? most of the phones do, but you need to check this with your vendor.. If yes, you can just do "mls qos trust" on the interfaces connecting the HP Procurve.. again, you need to check with HP if they will pass the DSCP values to the upstream switches, and not reset it.. because if HP switch resets the DSCP value, i dont think we can implement qos here... very important point here is "QOS DIFFSERVE IS END - TO -END".. so we need to take care of each component through which the traffic passes...

Incase your ip telephony vendor does not support automatic DSCP values, you need to force DSCP values on your primary 3560, by classifying the traffic and marking it on the edge... you can configure an ACL - for traffic from voice vlan, and mark the traffic as DSCP EF.. as given in the following URL:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3560/software/release/12.2_25_se/configuration/guide/swqos.html#wp1032145

If HP switch passes the DSCP values, your 3560 will trust the DSCP and carry EF for the voice traffic, and CS3 for signalling.. again, on the outbound 3560 switch where the metro link terminates, you can just trust the DSCP values to make sure voice traffic is prioritized..

One more question - do you have control of the network on the other side of metro link ? If not, again, your qos configuration will be unidirectional, and will not be that effective !

Hope this helps.. all the best..


Raj

juan-ruiz Fri, 01/29/2010 - 12:54

Very much appreciated your nice explanations as I read the links, gather my information it starts to make more sense putting all the pieces together.
Ok answers to your questions.

1.       So ,if i understand right, you have a 3560, connecting to your HP procurve edge switches ? Is this a layer 2 connection? Yes I have a 3560G with the enhanced image and full IP routing support. This is the main switch and all HP switches connect to this hub switch. The Cisco and HP are layer 2 trunk connections between them.

2.       One important question here is, - does the IP phone tag EF automatically to the switches? Yes they do. I’m not sure if the HP resets the DSCP values or not. Need to investigate this.

3.       One more question - do you have control of the network on the other side of metro link? Yes I do this is another Cisco 3560 G with the enhanced image.

High-level summary of implementation tasks with assumptions for strategy A:

1.       If the HP switches pass the DSCP values and phones tag EF to the switch then auto Qos will work by enabling this feature on the layer 2 trunks that connect each HP edge switch.

2.       I would also enable auto qos on the switchport interface that connects the Metro E at corporate and at the terminating side in the data-center.

With the above solution implemented this would get QoS working and my voice would have priority.

High-level summary of implementation tasks with assumptions for strategy B:

1.       In the event that the HP switches do not pass the DSCP values I would need to mark the voice traffic with an access-list and force DSCP values on the matching access-list by setting the values.

2.       On the other side of the Metro E terminating switch (Cisco 3560) I can enable auto QoS on the Metro E port and traffic would get the priority since it is coming with the DSCP values that I forced on the voice Vlan.

The solution B would be required only if the HP switches do not pass the DSCP values.

Anything else I’m missing?

Thanks a bunch

Kind regards,

Juan

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