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My current solution for dedicate internet link for specific applications (eg. skype) is to use PBR with static destination of Skype servers IP addresses.

But unfortunately IP address may change/add, and we have to manually configure them in PBR. So I want to think for another way to do this solution. One I can think of is to use some DPI marking DSCP and have routers to do PBR by DSCP marked. But I am still not sure if it will accurate enough.

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  • First of all what appliance are you using "dedicating" BW? Next in line: do you experience trouble with Skype only or are there other services in need of BW? – laf May 29 '13 at 8:04
  • It is just a Cisco router to redirect IP traffic that go to skype server to dedicate internet link. Skype is our current problem application because user want to have a video call that need good qos for delay, bw, jitter. – nuttee May 29 '13 at 8:10
  • I see you're doing this outbound, but what about inbound? – mellowd May 29 '13 at 8:16
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    I solved similar problem few years ago with 'joost' by launching 'joost' as dedicated user and then IPFW in OSX to SNAT that user. Then I knew on my CSCO router that packets from this IP address are always from joost application. But this solution does not work in Windows. I wonder if there is way for skype to set its PREC/DSCP value? Or if there is external program to set PREC/DSCP per PID? – ytti May 29 '13 at 8:36
  • I can't post this as an answer because I have never done it and can't provide any config examples etc, but you can find examples easily enough on the Internet. If your router supports it, use NBAR. – jwbensley May 29 '13 at 8:57
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In Windows you could use Policy Based QoS to set DSCP matching on the application name (applied through group policy)

edit: document refers to Server 2008 but the feature seems to available on Windows 7 Desktop as well

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  • Thanks! I haven't heard this feature before. This one is good to trust by Windows qos configuration. Better than DPI, because I am still not sure if DPI can match all protocol accurately or not. – nuttee May 29 '13 at 9:25
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    If this works as advertised, then it's indeed a solution as well if you use Windows. Does not help you if you have other operating systems like linux, mac, iphone, android though. – Stefan Radovanovici May 29 '13 at 9:45
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Starting with IOS 12.4(4)T NBAR can be used to classify skype traffic. You could use a class map to mark skype traffic, something like this:

class−map match−any skype_traffic
 match protocol skype

Then use that class-map with PBR instead of the ACL matching the skype servers IP Addresses.

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  • This is much better than using Skype_IP_servers. It it to be tested how good does NBAR works along with Skype. Starting 2013, NBAR2 took it to a new level, but it will require more resources and basically you need ISR G2. – laf May 29 '13 at 9:27
  • Have anyone tested nbar2 with skype? I have a bad experience with nbar2 to classify bitorrent. – nuttee May 29 '13 at 9:42
  • Unfortunately I haven't used it personally, I just heard it's working. Some test is probably in order. – Stefan Radovanovici May 29 '13 at 9:48
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if the destination IP addresses stay the same - why not simply using static routes pointing to the dedicated link you mentioned? this way you take away the need for the router to look at each match criteria you have set.

e.g. 'skype' server ip address = 10.1.1.1 and 2nd link is 192.168.1.2

ip route host 10.1.1.1 192.168.1.2

I have a similar situation where broadcasting services are handled via a 2nd link. no pbr needed for this.

I used PBR before - but that was in order to have specific sources using specific gateways on the same network.

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