Solved: QoS

blank.blank · ‎05-01-2010

Hi

Hope someone can help.

Does any know of a way to prioritise UDP traffic coming out of a switchport without enabling QoS on the switch?

The reason I ask is that two types of data are coming into the switch (Switch A) one is UDP based and the other TCP based. Both types of data originate from the same device and can potentially come in on any of 10 access ports on the switch. No QoS rules should be configured on the switch for these ports, as this is a strong recommendation from the manufacturers of the device.

Switch A has a trunk port to another switch. This trunk port carries some of the TCP data and all of the UDP data from the originating device. I would like to prioritise the UDP data on this link without having to add QoS rules to the access ports on Switch A.

I understand that it might not be possible to do this as I will need to classify the data as it comes into the access ports on Switch A. But this will require enabling QoS on the switch. I was hoping there would be a way to take advantage of the differing protocols without enaling QoS?

Many Thanks

Mike

Jon Marshall · ‎05-01-2010

No QoS rules should be configured on the switch for these ports, as this is a strong recommendation from the manufacturers of the device.

Hmmm, sounds like you may want to replace the switch Unfortunately this is exactly what QOS was designed for ie. giving priority to some traffic and not to others. You could have another uplink from the switch to dedicate to UDP traffic but the problem then becomes how to classify the UDP traffic.

If the UDP traffic was in a different vlan then you could do it by only allowing that vlan on the other link. If the switch was a L3 switch and routed the traffic you could use something like PBR if supported to redirect the traffic etc.... But all of the above would be a "fix" where the proper solution is indeed QOS.

Any reason why the manufacturer is recommending not run QOS ?

Jon

View solution in original post

Jon Marshall · ‎05-01-2010

blank.blank wrote:

No sorry, the switch is fine, it is a cisco 3570.

The problem is that the manufactures of the device that is connected to the switch do not recommend enabling QoS on the switch ports that it connects to. This is becuase it can have negative impact on performance,

cheers

mike

Mike

I would try it anyway. The 3750 supports vlan based QOS so i would try using that.

Jon

View solution in original post

Jon Marshall · ‎05-01-2010

No QoS rules should be configured on the switch for these ports, as this is a strong recommendation from the manufacturers of the device.

Hmmm, sounds like you may want to replace the switch Unfortunately this is exactly what QOS was designed for ie. giving priority to some traffic and not to others. You could have another uplink from the switch to dedicate to UDP traffic but the problem then becomes how to classify the UDP traffic.

If the UDP traffic was in a different vlan then you could do it by only allowing that vlan on the other link. If the switch was a L3 switch and routed the traffic you could use something like PBR if supported to redirect the traffic etc.... But all of the above would be a "fix" where the proper solution is indeed QOS.

Any reason why the manufacturer is recommending not run QOS ?

Jon

blank.blank · ‎05-01-2010

I do have the option of using a seperate link for the UDP traffic, but dont really want to go down that route. It is a layer 3 switch so should be able to do this without any probs.

The manfactures states that enabling QoS on ports that connect to the device can have negative results.

I was hoping TCP flow control could help, in that while pause frames are sent via the second switch, UDP traffic can still be buffered by Switch A. This would mean having a large enough buffer on Switch A's trunk port. Im not sure if this can be set?

thanks

Mike

blank.blank · ‎05-01-2010

Accidentally clicked answered button....duh

Jon Marshall · ‎05-01-2010

blank.blank wrote:

Accidentally clicked answered button....duh

No worries, that's how i get most/all my points

Jon

Jon Marshall · ‎05-01-2010

Mike

I was hoping TCP flow control could help, in that while pause frames are sent via the second switch, UDP traffic can still be buffered by Switch A. This would mean having a large enough buffer on Switch A's trunk port. Im not sure if this can be set?

Really don't think this would be predictable enough to work the way you want it to. And to be honest, as i think you realise, it is just another workaround for the real solution. It's a strange switch that would provide negative effects if you enabled QOS. QOS is and has been a very important feature of networks, both LAN and WAN, for a long time now so unless the negative effects are clearly spelt out by the manufacturer when you purchased the switch i would be going back to them and asking exactly what negative effects there are and why.

Not trying to be unhelpful, it's just that you have to use the right tool for the job and in this case it is QOS.

Jon

blank.blank · ‎05-01-2010

No sorry, the switch is fine, it is a cisco 3570.

The problem is that the manufactures of the device that is connected to the switch do not recommend enabling QoS on the switch ports that it connects to. This is becuase it can have negative impact on performance,

cheers

mike

Jon Marshall · ‎05-01-2010

blank.blank wrote:

No sorry, the switch is fine, it is a cisco 3570.

The problem is that the manufactures of the device that is connected to the switch do not recommend enabling QoS on the switch ports that it connects to. This is becuase it can have negative impact on performance,

cheers

mike

Mike

I would try it anyway. The 3750 supports vlan based QOS so i would try using that.

Jon