Question on QoS ...

[sanjay.nadarajah]

Hi,

I have this configuration on a edge router that connects to the service provider.

-----------------------

Current configuration : 285 bytes

!

interface GigabitEthernet0/0

bandwidth 3000  <<<--------

ip address 172.17.32.254 255.255.255.240

no ip redirects

load-interval 30

duplex full

speed 100

media-type rj45

no keepalive

no cdp enable

service-policy output BLUECOAT_EGRESS

!

!

policy-map BLUECOAT_EGRESS

class VOICE_BEARER

    priority 960

   police rate 960000

     conform-action transmit

     exceed-action drop

class VIDEO_BEARER

   police rate 500000  burst 50000

     conform-action transmit

     exceed-action drop

    priority 500

class class-default

    fair-queue

     random-detect

-----------------------

The router is a Cisco 3825 and its not running any routing protocol. It just have a static

default route pointing to the IP VPN.

My question is with regards to the 'bandwidth 3000' command. From my monitoring tool, it peaks

upto 3M during the nights when the backup happens. So it seems that the 'bandwidth 3000' is

actually capping it to 3MB.

The setup is as follows :-

Cisco 3825 Router --> Packet Shaper (does compression) --> IP VPN.

Since it looks like the bandwdith command is actually capping it, I plan to increase the bandwidth

here to 6000 as the packet shaper will do compression on the packets.

So my question is :-

i) Does the bandwidth command cap the traffic to the amount set on the 'bandwdith x' ?

ii) Any other related suggestions to increase the BW for outbound traffic to the IP VPN ?

Thank you.

Cheers,

- SN -

[Mahesh Gohil]

Hi Sanjay,

It's not true that bandwidth is doing capping. BW command only provides reference to routing protocol and as you said it is not used in your case.

What I suspect is there must be capping at provider end which restrict to 3000 only and not you config because you put no limit on your class default queue.

Kindly ask your provider to provide config at his end or output of show policy-map interface

Hope this helps, also let me know if I am missing something

Regards

Mahesh

[Joseph W. Doherty]

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Posting

As Mahesh already noted, the bandwidth command informs other services of the amount of available bandwidth, it doesn't physically cap, and if you see the traffic rate peak at 3 Mbps, somewhere along the path you're being limited either logically or physically to that amount.

If there is such a limitation, it would make sense to reconfigure the policy map into a hierarchal policy shaping the overall traffic to the available bandwidth.  This so your two LLQ classes and the class-default WFQ engage when 3 Mbps is reached.

You might also remove the random-detect from class-default, since it's a very, very complex feature to use correctly and its defaults often are far from ideal.

Since your packet shaper is downstream of your router, I suspect the backup might already be using compressed packets.  Further, again for your policy to work correctly it needs to "know" available bandwidth.  Ideally then, you need your router downstream of the traffic shaper.  Depending on what the traffic shaper does, your router may no longer be able to correctly identify packets, which "breaks" your QoS policy.  Dealing with this often then requires doing QoS on the shaping device or tagging packets on the shaping device so they can be recognized by the router.

Lastly, you wrote traffic goes to "IP VPN".  If this VPN reduces MTU, that too needs to be addressed to maximize throughput.

[esomarriba]

Mahesh is right. The command "bandwidth" is use only for reference for routing protocol to make a smarter decision of the best path, BUT in your case you are not deploying any RP.

the bandwidth statement also helps applications like SolarWinds Orion, Netflow to determine the correct link capacity that you current buy from your SP.

Your question has been answer, please don't forget to give credit to Mahesh as he was the first to answer! Keep the community running!

HTH,

Elyinn.-

[esomarriba]

Hi Sanjay,

One more thing, make sure you don't have any rate-limit or bandwidth statement on your PacketShaper box, if you have let's say 3Mb/s on your PS, all your traffic will be cap to 3Mb/s no more! PS is very eficient doing this. So do your checklist and if you don't have any hard set limits call your SP.

HTH,

Elyinn.-