[c-nsp] Catalyst 6500 Snmp IfIndex Assignment Logic

Matlock, Kenneth L MatlockK at exempla.org
Thu Dec 8 20:06:13 EST 2011

What you want is:
"snmp-server ifindex persist"
That will make the ifindex values persist, even across a full chassis reboot. Get the mapping once, and then don't worry about it :)


From: cisco-nsp-bounces at puck.nether.net on behalf of Michael Balasko
Sent: Thu 12/8/2011 5:47 PM
To: cisco-nsp at puck.nether.net
Subject: [c-nsp] Catalyst 6500 Snmp IfIndex Assignment Logic


For the TL:DR crowd-
Does anyone know dead nuts how the Catalyst 6500 allocates SNMP ifindex numbers? Specifically the 6513/Sup720-10Gig?

We are converting our Core infrastructure switches from CatOS to IOS(YAY!)  and we have nearly 500 devices plugged into EACH of these monsters(WOW). The ifindexes of course are going to change and I would like to be able to predict them (HAHAHAH) to what they will be and or figure out if I can manipulate them such that I can have a script ready to realign our monitoring and trending systems.

I normally would take a same chassis and build the switch identical(Line card wise) to what is being converted and then when I swap the SUP's they all line up but in this case I am up the brown fecal river, paddle-less.

I've called TAC but I  got the we dunno its not supported answer.

More subtext:
I flipped a  Sup720 from Cat to IOS and then deleted the ifindex table from nvram: and then followed it up with a write erase. I powered off the switch, pulled every line card out and then powered up the switch. When the SUP was back alive I inserted a 6148TX into slot 3 and got an index number of 77 as the start index. The old one is 86.  I see that the Sup starts at 1 and the rest to me is not really decipherable.

So does anyone know the answer or THE 6K guy that knows who I could ask using beer or whatever beverage choice he would like?

Michael Balasko
Network Specialist II
City of Henderson
240 Water St.
Henderson, Nv 89015

Coincidence, n.:
  You weren't paying attention to the other half of what was going on.

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