[nsp] Help with QoS

[Stephen Sprunk]

Thus spake <francisv@dagupan.com>
> I wanted to prioritize traffic coming from two workstations connected to a
> 2924 catalyst switch. The workstations are Windows Media encoders and serve
> traffic to Windows Media server/reflectors over a WAN link. On some
> occasions, the WAN link gets congested and the session between the encoders
> and servers is cutoff.
> 
> Here's the network layout:
> 
> [MS encoder machines]
>        |
> [Catalyst 2924]  
>        |        +--E1-->[to Cisco 1750 @ local IX]
>        |       /
> [Cisco 3640]--+
>                \
>                 +--E1-->[to Cisco 7206 @ core]
> 
> I labeled the packets on the ports where the encoders are connected with a
> value of 5:
> 
> interface FastEthernet0/18
>  description MS Media Encoder 1
>  duplex full
>  speed 100
>  switchport priority default 5
> !
> interface FastEthernet0/19
>  description MS Media Encoder 2
>  duplex full
>  speed 100
>  switchport priority default 5
> 
> and on the Cisco 3640, I created a class-map to match the COS from the
> switch and then do some stuff to it in a policy-map:
> 
> class-map match-all COS5
>  match cos 5
> 
> policy-map HIGH-PRIORITY
>  class COS5
>   set ip dscp 10
>   priority 128 
> 
> and then applying that to the outgoing interface:
> 
> c3640-noc-cal(config-if)#service-policy output HIGH-PRIORITY
> 'match cos' supported only with IEEE 802.1Q/ISL interfaces
> 
> I'm assuming that COS is not carried all the way to the router from the
> switch. Is there any other way around this? Will DSCP be carried over the
> WAN interface? I'd like to also look at the DSCP tag once it reaches other
> routers within our administrative control.

COS != DSCP

Use this on your router:

!
class-map COS4
 match cos 4
!
policy-map cos-to-dscp
 class COS4
  set dscp 33
!
class-map AF41
 match dscp 33
!
policy-map cos4-128k
 class AF41
  bandwidth 128
!
interface [from 2950]
 sevice-policy input cos-to-dscp
!
interface [to E1]
 service-policy output cos4-128k
!

S