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Cisco ASR 901 Series Aggregation Services Router Software Configuration Guide
OL-23826-09
Chapter 24 Configuring QoS
Configuring Quality of Service (QoS)
• On all Cisco ASR 901 routers, you can attach per-port and per-port, per-VLAN policy-maps across
all ports on the router until QoS classification resource limitations are reached. Any policy
attachment or change that causes this limit to be exceeded fails with a TCAM resources exceeded
error message.
Sample QoS Configuration
The following configuration demonstrates how to apply QoS given the hardware limitations. The
Cisco ASR 901 processes traffic between interfaces as follows:
• For layer 2 traffic passing between the GigabitEthernet 0/2 interface and the GigabitEthernet 0/0
interface, the output queue is determined by the QoS Group assigned in the in-qos policy map.
• For layer 3 traffic passing between GigabitEthernet 0/2 interface and the GigabitEthernet 0/0
interface, the output queue is determined based on the CoS value assigned in the in-qos policy map.
(the CoS value is mapped 1:1 to the QoS group value.)
• For traffic passing between other interfaces, the output queue is determined based on the CS fields
(top three bits) of the IP DSCP bits; these bits are copied to the CoS bits, which are mapped 1:1 to
the QoS group value.
!
class-map match-all q0
match qos-group 0
class-map match-all q1
match qos-group 1
class-map match-all q2
match qos-group 2
class-map match-all q3
match qos-group 3
class-map match-all q4
match qos-group 4
class-map match-all q5
match qos-group 5
class-map match-all q6
match qos-group 6
class-map match-all q7
match qos-group 7
class-map match-any Voice
match dscp ef
class-map match-any Signaling
match dscp af41
class-map match-any HSDPA
match dscp af11 af12
class-map match-any TCAM1
!translates to 3 TCAM rules because each match in match-any uses one entry
match dscp af21
match cos 3
match mpls experimental topmost
class-map match-all TCAM2
!translates to 1 TCAM rules because all the match-all clauses together take only 1 entry
match dscp af21
match cos 3
match mpls experimental topmost 1
!
policy-map in-qos
class Voice
set cos 5
set qos-group 5
class control_plane
set cos 4