KBI 311574 Issue Addressed: DeviceMagic Generates Inaccurate Bandwidth Usage For High Speed CISCO Devices
Version
Argent Advanced Technology 5.1A-1707-F or below
Date
Tuesday, 12 September 2017
Summary
CISCO devices might provide one or both sets of interface counters based on RFC1213 and RFC2233 respectively
The ifTable in RFC1213 is the traditional interface counters that almost all SNMP devices support
The ifTable defines 32-bit counters for inbound and outbound octets (ifInOctets/ifOutOctets) that are used for bandwidth calculation
The issue of 32-bit counters for high speed CISCO devices is that it wraps over too quickly
For example, a 10 Mbps stream of back-to-back, full-size packets causes ifInOctets to wrap in just over 57 minutes
At 100 Mbps, the minimum wrap time is 5.7 minutes, and at 1 Gbps, the minimum is 34 seconds
If the counter wraps more than once between Relator interval, the calculation is no longer valid
The ifXTable defined in RFC2233 implements 64-bit counters ifHCInOctets/ifHCOutOctets to address the issue
DeviceMagic in Argent Advanced Technology 5.1A-1707-F and earlier support RFC1213 only
As a result, the bandwidth calculation might not be accurate for high speed CISCO devices
The issue has been addressed in Argent Advanced Technology 5.1A-1707-G
Technical Background
DeviceMagic in Argent Advanced Technology 5.1A-1707-G is enhanced to support RFC2233
NOT ALL CISCO DEVICES SUPPORT 64-BIT COUNTERS
Even more important, the same device may or may not support 64-bit counters depending on the release of the operating system
An example of this extremely confusing situation is shown below:
- Catalyst 2950 and 3550 – Support begins in Cisco IOS Software Release 12.1(11) EA1 since Cisco bug ID CSCdx67611 and Cisco bug ID CSCdw52807
- Catalyst 2900XL and 3500XL – Support begins in Cisco IOS Software Release 12.0(5) WC3 since Cisco bug ID CSCds45300
- Catalyst 5000/6000 ATM modules – Since Cisco IOS Software Release 12.0(14) W05 (20), refer to Cisco bug ID CSCds07238
Check your devices’ IOS level very carefully
Note: Cisco IOS Software does not support 64-bit counters for interface speeds of less than 20 Mbps
This means that 64-bit counters are not supported on 10 Mb Ethernet ports
Only 100 Mb Fast-Ethernet and other high speed ports support 64-bit counters
Resolution
Upgrade to Argent Advanced Technology 5.1A-1707-G or above
In order to support 64-bit interface counters, the device must be configured to use SNMPv2c or SNMPv3 protocol, and explicitly set to use option RFC2233 or option ‘Dynamically Determined’ to allow Engine to determine
