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Polling 32-bit or 64-bit InOctets

Unanswered Question
Jun 2nd, 2009
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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

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David Stanford Tue, 06/02/2009 - 08:02
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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.



gnijs Tue, 06/02/2009 - 09:08
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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

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