Difference between setting QoS on WAN vs. LAN

[LarryT2012]

Hi All,

We have a remote site that is experiencing garbled voice issues that appears to be pointing to QoS.  The set-up of the network pre-dates me, but I noticed that we have two Cisco Edge routers (one with Class/Policy Maps and the other without), and that Class/Policy Map statements have not been applied to the interface via Service Policies.  I also have an identical set-up for the Cisco Switch LAN device that connects to the routers as it too has Class/Policy Maps that are not applied to the interface.

Which is better, to have QoS applied to the LAN or WAN in a network?

-Larry

[Mark Malone]

Hi Larry

You should have it set as both really lan and wan if possible  , qos should be marked from source right through to the destination but a lot of opeople just chose to do WAN and it works fine for them

sometimes there is no need  for it at the LAN as there gig or 10gb pipes depending on devices and hardly ever fully utilized and qos really has full an effect where the bottleneck is at the wan bit its still good to mark through the LAN to the WAN  , so it should at least be correct on WAN interfaces on both sides to make sure your EF voice traffic gets prioritized where there is congestion

LAN qos is not MQC though , its MLS or Auto Qos depending again on platform but enabling some forms of Auto Qos at LAN level can automatically create class-maps and policy maps which it uses but there not manual like WAN side

if your using voice its best practice to at least have it prioritized at the wan , I would look at that first before going near the LAN unless the LAN is heavily congested too

This is a good guide for MQC shows voice setup in it too may help you get going

https://supportforums.cisco.com/document/32286/common-qos-configurations-wan-link-using-mqc

[LarryT2012]

Hi Mark,

Thanks for the response.  I've applied QoS on our outbound Edge device and am still experiencing garbled audio issues.  Whats the difference between applying QoS outbound vs inbound on the WAN connected interface?

-Larry

[Mark Malone]

Hi

input qos usually goes on lan interface output on wan , did you do the other router at the end of the link as well, putting it on just one end may not help as there may be congestion on both sides and the voice would need to be carried through both congested routers with priority marking  , is this across an mpls circuit or some other private service ? just making sure its not going over internet qos doesn't work well on internet if not tunnelled

whats the average utilization on this link is it being hammered ?

[Joseph W. Doherty]

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Posting

Which is better, to have QoS applied to the LAN or WAN in a network?

QoS should be implemented wherever there's congestion that's adverse to the service needs of the traffic (this is also assuming QoS can mitigate).

So to your question, LAN vs. WAN QoS, neither is really "better" although as WANs often provide less bandwidth than LANs, WANs more often benefit from QoS.