Wireless Access

I have about 64 Aruba AP135 connected to two Cisco 3850 Cisco switches.

I noticed that there are a large number of input errors on the switchport interface for each AP135. Although, the errors tend to appear more on the AP135 that service clients. The AP135 that are Spectrum Monitors do not show same large number of input errors like the other APs.

Here is example from one AP135.

Received 88182 broadcasts (88153 multicasts)
0 runts, 0 giants, 0 throttles
22033 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored
0 watchdog, 88153 multicast, 0 pause input
0 input packets with dribble condition detected

The input errors do not appear to impact client connectivity. However, I'm not certain of the cause of the errors.

The errors appear on both Cisco 3850 switches for each AP. The ports are configured as switchport access mode.

Duplex/Speed are set to auto. And spanning-tree portfast and bpduguard are enabled.

Anthony,

This is most likely due to MTU Path DIscovery. Check out this article for details:

http://community.arubanetworks.com/t5/ArubaOS-and-Controllers/Oversize-jumbo-frame-errors/m-p/5421/highlight/true#M1860

Best regards,

Madani

Hi Madani,

Thanks for the quick response and documenation. I took a look at the document. I see that there is mention of Jabbers and CRC errors along with oversize errors.

I have one other question about the document. The document doesn't mention input errors. Is 'oversized' the same as 'input?

Also, I see the large number of input errors on APs that service clients and not the AP configured as Spectrum Sensors. Should I see the same number of input errors on both or are the Spectrum Sensors capable of generating input errors?

I checked the configuration of AP System on the controller. Currently, the SAP MTU field is empty. Nothing exists in the field.

Though, I did check and verify the switchport configuration on the 3850. The MTU is set for 1500 bytes.

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@anthony.l.brice wrote:

Hi Madani,

 

Thanks for the quick response and documenation. I took a look at the document. I see that there is mention of Jabbers and CRC errors along with oversize errors.

 

I have one other question about the document. The document doesn't mention input errors. Is 'oversized' the same as 'input?

 

Also, I see the large number of input errors on APs that service clients and not the AP configured as Spectrum Sensors. Should I see the same number of input errors on both or are the Spectrum Sensors capable of generating input errors?

 

I checked the configuration of AP System on the controller. Currently, the SAP MTU field is empty. Nothing exists in the field.

Though, I did check and verify the switchport configuration on the 3850. The MTU is set for 1500 bytes.

 

 

 

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anthony.i.brice, please set the sap MTU to 1500 and see if the errors still keep going up.

I'll give that a try!

Thanks,

Anthony

I am curious about one other issue.

I have another site that has both 3400 series controller and AP135s running. Both sites are using the same controller OS version too: 6.2.1.4. 

However, the APs are connected to via Cisco 3750x instead of 3850.

When I check the port interface on the 3750x, there are no input errors. 

Even though, the controllers are setup identically, what would cause the input errors to appear on the Cisco 3850 switch and not the Cisco 3750x?

Anthony

Anthony,

I cannot tell you why.  I can only give you suggestions.

Anthony,

As Madani pointed, these errors are due to 'MTU probe packets sent by AP 135' (1578 bytes) at regular intervals.

On question regarding why errors seen/not-seen on one cisco model v/s other:
Can you confirm the MTU setting on on 3750x Cisco switch for ports where AP135 are connected, ? Is it same as that of 3850 or higher?

And as a work-around check if setting higher MTU than 1578 (ex: 9000) on 3850 switch ports helps?

fyi: oversized/giants are classified as Input-Error-Bytes.

regards,
-Vinay

3850 can be set to support Jumbo Frames.

The stack must be set to a value at the global level for L2 traffic ex: MTU 9000, this should be the command "system mtu jumbo 9000", and a reboot of the stack (all switches) is required after.

This enables the L2 frame size of 9000 on all ports, the reboot is required because the hardware ASICs get set up slightly differently on boot.

For Layer3 (routed) interfaces in vlans, you need to change the MTU on the VLAN if you want to routepackets larger than 1500, note that this also requires "system mtu jumbo 9000".

Hope this helps.