802.1p Marking from Cisco host IP for ARP replies

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Aug 6th, 2009
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I can't find the doc anywhere to answer my question so I'm am hoping someone can help me out ;)

I have a 3750 set as a gateway router on one of the VLANs. From a host somewhere out there on the VLAN I send an ARP request for the gateway address which is the 3750. The ARP is received by the 3750 as a tagged packet with pbit=0. The 3750 sends an ARP reply as expected but the pbit=7.

My question is why is the ARP reply marked with pbit=7? I have my hunches as to why but I usually get into trouble when I assume.

I'd really appreciate the feedback.


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Istvan_Rabai Thu, 08/06/2009 - 04:52
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I tried to find a document on the Cisco website supporting this but I haven't found one, so my supposition is the following:

ARP replies originated by the Cisco devices are treated as Network Control frames, just like spanning-tree bpdus, therefore they are set with CoS=7.



gliverm Thu, 08/06/2009 - 04:55
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Thanks for the feedback. This is my theory too from some other experience I have.


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