802.1p Marking from Cisco host IP for ARP replies

gliverm · ‎08-06-2009

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.

Gayle

Istvan_Rabai · ‎08-06-2009

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.

Cheers:

Istvan

gliverm · ‎08-06-2009

Thanks for the feedback. This is my theory too from some other experience I have.