[tkined] relating Cisco Catalyst physical port-to-dot1dTpFdbPort instance

From: William B. Clay (william.b.clay@acm.org)
Date: Tue Aug 08 2000 - 03:10:40 MET DST

>>I've only worked with Catalyst 5x00's, but I believe the trick is the
>>append the VLAN number to the community string, thus:
>>For example: public@101. This actually IS documented somewhere, but it's
>>well-hidden and took me a long time to find it. Maybe they want us to buy
>>CWSI instead?

>Wow! You don't know how long I've been trying to figure
>out how to get that data!
>Now, the next inevitable question is, how do you map the
>dot1dTp ports into actual physical ports? The dot1 ports
>all appear to be virtual (starting at some arbitrary
>number and incrementing)

Oh, yeah, I left out that part. Sorry. It's indirect (at least I haven't
found a better way). Walk the MIB variable portCrossIndex, whose instance
index is slot & port and whose value is that virtual bridge port number,
then match 'em up with the dot1dTp instance indexes. You probably want to
walk by slot and port anyway to get things like VLAN, link status, port
name, etc., so just get portCrossIndex while you're at it.

Why they didn't choose to use ifIndex for dot1dTp's instance index mystifies
me. Maybe it allows them to avoid changing the indices if a board is
hot-swapped to a different slot. One thing it does handle ... on
group-switched ports (still got any?), a group of 12 sequential ifIndexes
all have the same portCrossIndex as the first port of the group, since all
12 physical ports are logically all on the same bridge port. In this case,
I know of no way to determine which MAC is on which physical port -- you
only know the group.

-- Bill Clay
Charlotte NC

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