06-02-2009 06:01 AM
Hi all,
Can someone shed some light on when to poll 32-bit and when to poll 64-bit counters IfInOctet and IfHCInOctets ?
* Which counters are supported on which interfaces ?
I have seen routers which don't support the 64-bit counters (probably because it is not needed on a T1 interface for example). But i have also seen a 3750 switch which doesn't support it on a 1G interface (i assume this can be fixed with a firmware upgrade, no ?). However, are there any "rules" used by Cisco to determine when to support or implement the 64-bit counters ?
(i just converted all my graphs to 64-bit counters, now 20% of the graphs don't seem to support this counters. Before, i had 100% graphs, but any speed above 120 Mbit was inaccuratly graphed)
regards,
Geert
06-02-2009 08:02 AM
According to RFC 2863, interfaces with an interface speed (ifSpeed) of 20M
bps and higher must instantiate the ifHC*Octets objects. The interfaces
without these objects are probably slower than that.
Actually, the RFC says that you only instatiate 32-bit counters for
interfaces with ifSpeed <= 20Mbs. You implement both for interfaces with
20 Mbs > ifSpeed < 650Mbs. After that, it's only 64-bit
counters.
It is a trade-off between the speed of the interface and the minimum time
to wrap. The 2863 guideline is provide 64-bit counters for interfaces
which might wrap in less than an hour.
That means that a 10/100Mbs
interface needs to provide 64-bit counters, but when the interface is
running at 10Mbs, it doesn't make any sense to disable the 64-bit
counters even though using the 32-bit counters is just fine. Even for
(fixed) higher-speed interfaces, if someone is willing to poll
them at the required rate, then it's fine to use them.
06-02-2009 09:08 AM
Thanks you for your comments.
Can i conclude from your comments, that if the interface "might" wrap within an hour at maximum speed, Cisco will provide 64-bit counters, no matter what the actual speed is.
For example a 10/100/1000 interface might wrap easily within an hour at 1000 Mbps, but not at 10Mbps, so 64-bit counters are provided anyway, even when it run at 10 Mbit (speed 10) ??
(even though it is not strictly needed by the RFC at this speed ?)
regards,
Geert
06-02-2009 01:45 PM
I found this link which answers a lot of questions:
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_q_and_a_item09186a00800b69ac.shtml
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