Using QoS LLQ to prioritise your video and voice traffic

It has been a good week for me in terms of studying for the CCDA and at work. Learned a lot of new things such as QoS particularly LLQ and Pseudowire over Cisco’s ME. This blog I will focus more into QoS. Low-latency queing is a QoS feature developed by Cisco applying stricter policy queing  to Class-based weighted fair queing (CBWFQ).

LLQ is best applied when you have a network that has video and voice running. We know that they are very sensitive to jitter/delay. You have to make sure that voice/video packets gets preferential treatment over data. In my scenario, I have a customer who has a 881 Cisco router on-site that needed to connect to their VoIP system on a data center.

The requirements are to mark video traffic with af31 and voice with ef. Both are to have 10 percent each of the traffic bandwidth which is 20Mbps. Voice and video are on vlan 10. I am marking traffic as they go into the LAN interface and set classify and prioritize traffic as they go out of the WAN.

class-map match-any video-traffic
match dscp af31
class-map match-any voice-traffic
match dscp ef

policy-map WAN-EDGE-OUT
class voice-traffic
priority percent 10
class video-traffic
priority percent 10
class class-default
fair-queue
32
interface FastEthernet4
band 20000
ip nbar protocol-discovery
service-policy output WAN-EDGE-OUT
exit

! LAN Interface QoS To MARK Traffic.

ip access-list extended CISCO
permit ip any any

class-map match-any MARKING-video-traffic
match access-group name CISCO

class-map match-any MARKING-voice-traffic
match protocol rtp

policy-map MARK-TRAFFIC
class MARKING-voice-traffic
set dscp ef
class MARKING-video-traffic
set dscp af31
Interface vlan 10
ip nbar protocol-discovery
Service-policy input MARK-TRAFFIC

Pretty neat stuff….you noticed I activated ip nbar protocol-discovery. To know more about that command, I have another blog regarding it.

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