On Oct 26, 2011, at 10:00 AM, Dave Sparks wrote:
> Any pointers on how to filter out PVST packets?
>
> # tshark -i vlan701 not stp
> Capturing on vlan701
> 0.000000 Cisco_6a:50:13 -> PVST+ STP RST. Root = 0/1/00:12:f2:94:dc:00 Cost = 7 Port = 0x8013
> 2.013488 Cisco_6a:50:13 -> PVST+ STP RST. Root = 0/1/00:12:f2:94:dc:00 Cost = 7 Port = 0x8013
> 4.026868 Cisco_6a:50:13 -> PVST+ STP RST. Root = 0/1/00:12:f2:94:dc:00 Cost = 7 Port = 0x8013
> 6.039309 Cisco_6a:50:13 -> PVST+ STP RST. Root = 0/1/00:12:f2:94:dc:00 Cost = 7 Port = 0x8013
PVSTP+ does *NOT* use the standard Ethernet type or LLC SAP for STP; instead, it uses SNAP and an OUI of 00:00:0C and a protocol ID of 0x010b. Unfortunately, there's no simple primitive to check for SNAP+{OUI}+{Protocol ID}. The way you way you do that is dependent on the link layer type; for Ethernet I think it'd be
ether[12:2] <= 1500 and ether[14:4] == 0xaaaa0300 and ether[18:4] == 0x000c0010b
