QoS Cisco 887 - DNS prioritize traffic

[Federico Olivieri]

Hi All,

I'm trying to implement QoS on my Cisco 887 and prioritize DNS packet that comes into ADSL interface and they go to my server. Here the topology

ADSL--->CISCO887--->Firewall--->Server

Cisco router has a Dialer interface that provide PPPoE. The Dialer is configured under ATM interface. The FastEthernet interf where the server is connected is under Vlan 1. That is what I have done so far but I m not sure if it works of I nissed some steps

policy-map QoS_DNS_NTP
class NBAR_DNS
bandwidth 512
class NBAR_NTP
bandwidth 96

policy-map QOS
class class-default
shape average 900000
service-policy QoS_DNS_NTP

policy-map DNS_PREC
class NBAR_DNS
set ip precedence 4
class NBAR_NTP
set ip precedence 3

interface Vlan1
ip address 192.168.0.1 255.255.255.0
ip nbar protocol-discovery
service-policy input DNS_PREC
service-policy output DNS_PREC

interface Dialer1
ip nbar protocol-discovery
service-policy input DNS_PREC
service-policy output QOS

Can you please let me know if is it correct? I need to prioritize traffic in both directions.

Thanks to everyone

[Joseph W. Doherty]

Disclaimer

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Posting

Yea, looks like it should work.  However, assuming you only have the two interfaces, you don't need the ingress and egress DNS_PREC policy statements (as both should be marking the same traffic).  Also you don't need to enable NBAR protocol discovery on your interfaces to use NBAR protocol matching in your (not shown) class-maps.  Lastly, you can use explicit bandwidths in your QoS_DNS_NTP policy, but unless you're using an old IOS, using bandwidth percentages is little more flexible.

[Federico Olivieri]

Thanks for your reply Joseph. Just a last question: when I set the priority what is happen to the packet? is it just a mark put on the packet or the router put the marker and prioritize the packet?

Thanks

[Joseph W. Doherty]

Disclaimer

The Author of this posting offers the information contained within this posting without consideration and with the reader's understanding that there's no implied or expressed suitability or fitness for any purpose. Information provided is for informational purposes only and should not be construed as rendering professional advice of any kind. Usage of this posting's information is solely at reader's own risk.

Liability Disclaimer

In no event shall Author be liable for any damages wha2tsoever (including, without limitation, damages for loss of use, data or profit) arising  out of the use or inability to use the posting's information even if Author has been advised of the possibility of such damage.

Posting

"when I set the priority what is happen to the packet?"

Do you mean, when you mark packet with an IP Precedence?  If so, what you've done is set the first 6 bits of the ToS byte.  What devices do with the ToS byte is up to them; often the default is they just ignore it.

[Federico Olivieri]

Thanks!