Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
Enterprise QoS Solution Reference Network Design Guide
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Catalyst 2950—<strong>QoS</strong> Considerations and <strong>Design</strong><br />
2-24<br />
<strong>Enterprise</strong> <strong>QoS</strong> <strong>Solution</strong> <strong>Reference</strong> <strong>Network</strong> <strong>Design</strong> <strong>Guide</strong><br />
Chapter 2 Campus <strong>QoS</strong> <strong>Design</strong><br />
cos: 0 1 1 2 2 3 3 4 4 5 5 6 7<br />
Cos-dscp map:<br />
cos: 0 1 2 3 4 5 6 7<br />
-------------------------------dscp:<br />
0 8 16 24 32 46 48 56 ! CoS 5 is now mapped to DSCP EF<br />
CAT2950#<br />
The Catalyst 2950’s hardware policers lack the granularity to implement the Conditionally-Trusted IP<br />
Phone + PC with Scavenger-Class <strong>QoS</strong> (Basic) Model, as illustrated in Figure 2-8. However, they can<br />
implement a simplified version of this model, as shown in Figure 2-11.<br />
Figure 2-11 Catalyst 2950—Conditionally-Trusted Endpoint Policing: IP Phone + PC with<br />
Scavenger-Class <strong>QoS</strong> (Basic) Model<br />
Start<br />
VVLAN<br />
ANY<br />
No<br />
DVLAN<br />
ANY<br />
Yes<br />
Yes<br />
1 Mbps<br />
5 Mbps<br />
It should be kept in mind that the coarse granularity of the Catalyst 2950’s policers (which are configured<br />
in 1 Mbps minimum increments on FastEthernet interfaces) could potentially allow up to 1 Mbps of<br />
traffic mimicking legitimate voice traffic per conditionally-trusted switchport.<br />
The configuration for configuring a switchport to conditionally trust an IP Phone that has a PC connected<br />
to it, with Scavenger-class <strong>QoS</strong>, is shown below.<br />
Example 2-9 Catalyst 2950—Conditionally Trusted IP Phone + PC with Scavenger-Class <strong>QoS</strong> (Basic)<br />
Model<br />
CAT2950(config)#mls qos map cos-dscp 0 8 16 24 32 46 48 56 ! Maps CoS 5 to EF<br />
CAT2950(config)#<br />
CAT2950(config)#class-map VVLAN-ANY<br />
CAT2950(config-cmap)# match access-group name VVLAN-ANY<br />
CAT2950(config-cmap)#class-map DVLAN-ANY<br />
CAT2950(config-cmap)# match access-group name DVLAN-ANY<br />
CAT2950(config-cmap)#exit<br />
CAT2950(config)#<br />
CAT2950(config)#policy-map IPPHONE+PC<br />
CAT2950(config-pmap)# class VVLAN-ANY<br />
CAT2950(config-pmap-c)# police 1000000 8192 exceed-action drop<br />
! Out-of-profile traffic from the VVLAN is dropped<br />
CAT2950(config-pmap-c)# class DVLAN-ANY<br />
CAT2950(config-pmap-c)# set ip dscp 0<br />
! Optional remarking in case the trust boundary is compromised<br />
CAT2950(config-pmap-c)# police 5000000 8192 exceed-action dscp 8<br />
! Out-of-profile data traffic is marked down to Scavenger<br />
CAT2950(config-pmap-c)#exit<br />
CAT2950(config-pmap)#exit<br />
CAT2950(config)#<br />
CAT2950(config)#<br />
CAT2950(config)#interface FastEthernet0/1<br />
CAT2950(config-if)# switchport access vlan 10<br />
CAT2950(config-if)# switchport voice vlan 110<br />
CAT2950(config-if)# mls qos trust device cisco-phone ! Conditional trust<br />
No<br />
No<br />
Yes<br />
Yes<br />
Trust and Transmit<br />
Drop<br />
Re-Mark to DSCP 0<br />
and Transmit<br />
Re-Mark to DSCP CS1<br />
and Transmit<br />
Version 3.3
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