877 QoS for VoIP over IPSEC

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Giuseppe Larosa Sat, 03/07/2009 - 04:09
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Hello Nikolaj,


you should do the following:


mark the VoIP packets with IP precedence 5 using a policy-map applied inbound to the LAN interface


on the ATM interface you can apply a service-policy outbound that provides an LLQ for packets with IP precedence 5.


A better setup for the ATM interface is that of using a two levels policy:

the parent policy-map shape all traffic just below the line rate.

a child policy implements LLQ and CBWFQ for traffic


access-list 111 permit udp lan-subnet lan-wildcard any range 16635 16635


class voip_inbound

match access-group 111


policy-map mark_voip

class voip_inbound

set ip prec 5



policy-map shape_all_traffic

class default

shape peak 2000000 (*)

service-policy out llq-cbwfq



class voice_outbound

match ip prec 5


policy-map llq-cbwfq

class voice_outbound

priority 256 (*)

class class-default

fair-queue



int atm0

service-policy out shape_all_traffic



(*) rates are only placeholders you need to identify the right values for your case


This works also if it is GRE over IPsec and it is based on the fact that the TOS of carried packet is copied to the external header


the command qos-preclassify can help too.


Hope to help

Giuseppe


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