# IPFW and Dummynet - Layer 2 Priority mapping behaviour



## lnichol (Jan 4, 2012)

Hi,

I am new to the FreeBSD forum and also to using Dummynet on FreeBSD. I have IPFW enabled on my FreeBSD workstation which is bridging two NICs to allow all traffic to pass through this device and on to its destination, a router. I have been successful in manipulating packet latency, packet loss and also DSCP markings at the Layer 3 level but now I need Dummynet to act upon my Layer 2 frame, specifically the Priority marking which is part of the 802.1q assignment (Priority 0-7). 

Does anyone know if Dummynet is capable of acting upon all levels of Class of Service, from 0-7? I'm not sure what rules can be set to make this work.

Thanks,

Lewy...


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## ecazamir (Jan 5, 2012)

dummynet uses ipfw to determine what packets are sent to pipes/queues. The answer is 'YES' if ipfw is able to identify what packets you want.


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## lnichol (Jan 5, 2012)

That sounds good. 

So, let's say I wanted to use a packet/frame loss rule (20%) on all layer 2 frames that had a p-bit/Class of Service Priority mapping of 5. How would I set this rule in Dummynet?


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## ecazamir (Jan 6, 2012)

I assume you try to use a FreeBSD machine as a bridge for a 802.1q VLAN tagged link.
AFAIR, 802.1p PCP (Priority Code Point) is a part of the 802.1Q header and can't be used on non-802.1q frames.

It looks like the current IPFW implementation (8.2-RELEASE, 9.0-x) lacks packet matching based on the values of the 802.1q header fields.
As long as the packets can't match, you can't send tem to dummynet pipes/queues.


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