this took far too long to find, longer than a walk to the data center. I’ve removed the serial numbers to protect the innocent. I just wanted to list card models without reading them off the card.

sw01#show inventory
NAME: “WS-C6509”, DESCR: “Cisco Systems Catalyst 6500 9-slot Chassis System”
PID: WS-C6509 , VID: , SN: xxxxxxxxxxx
NAME: “5”, DESCR: “WS-X6148-GE-TX 48 port 10/100/1000mb EtherModule Rev. 6.1”

I removed a bunch of lines there. I was trying to figure out why “switchport trunk encapsulation dot1q” wasn’t an option (there was no encapsulation option) on this card.

Finally found on Page 11 of this that these cards don’t support ISL, so they default to 802.1q:

WS-X6502-10GE
WS-X6548-GE-TX, WS-X6548V-GE-TX, WS-X6548-GE-45AF
WS-X6148-GE-TX, WS-X6148V-GE-TX, WS-X6148-GE-45AF

Which was important because I was seeing traffic on the host that didn’t appear tagged, and 802.1q doesn’t tag the native vlan (vlan 1) by default. Of course I have no idea what ISL traffic would look like in a tcpdump, probably thrown away as garbage, but who knows, better to see and know than to guess.