Wired Intelligent Edge (Campus Switching and Routing)

Problem:

When Aruba AP is connected to switch port it reports giant packets Rx on the interface.

MTU on the switch is set to default for AP Vlan which is 1522.

Verified MTU on Aruba AP under ap system-profile which is left at default as below,

(host) #show ap system-profile default


AP system profile "default"

---------------------------

Parameter                                Value

---------                                -----

RF Band                                    g

RF Band for AM mode scanning               all

Native VLAN ID                             10

Tunnel Heartbeat Interval                  1

Session ACL                                ap-acl

Corporate DNS Domain                       N/A

SNMP sysContact                            N/A

LED operating mode (11n/11ac APs only)     normal

LED override                               Disabled

Driver log level                           warnings

Console log level                          emergencies

SAP MTU                                    N/A

RAP MTU                                    1200 bytes

LMS IP                                     N/A

Backup LMS IP                              N/A

LMS IPv6                                   N/A

Backup LMS IPv6                            N/A

LMS Preemption                             Disabled

LMS Hold-down Period                       600 sec

LMS ping interval                          20

Remote-AP DHCP Server VLAN                 N/A

Remote-AP DHCP Server Id                   10.10.10.1

Remote-AP DHCP Default Router              10.10.10.2

Remote-AP DHCP DNS Server                  N/A

Remote-AP DHCP Pool Start                  192.168.1.1

Remote-AP DHCP Pool End                    192.168.1.50

Remote-AP DHCP Pool Netmask                255.255.255.0

Remote-AP DHCP Lease Time                  0 days

Remote-AP uplink total bandwidth           0 kbps

Remote-AP bw reservation 1                 N/A

Remote-AP bw reservation 2                 N/A

Remote-AP bw reservation 3                 N/A

Remote-AP Local Network Access             Disabled

IPM activation                             Enabled

IPM power reduction steps with priorities  disable_usb/priority:2

IPM power reduction steps with priorities  cpu_throttle_25/priority:1

Bootstrap threshold                        8

Double Encrypt                             Disabled

Dump Server                                N/A

Heartbeat DSCP                             0

Management DSCP                            N/A

IP DSCP to VLAN 802.1p priority mapping    N/A

Maintenance Mode                           Disabled

Maximum Request Retries                    10

Request Retry Interval                     10 sec

Number of IPSEC retries                    85

Secondary Master IP/FQDN                   exit

AeroScout RTLS Server                      N/A

RTLS Server configuration                  N/A

RTLS Server Compatibility Mode             Enabled

Slow Timer Recovery by rebooting itself    Disabled

Telnet                                     Enabled

Disable RAP Tftp Image Upgrade             Disabled

Spanning Tree                              Enabled

AP multicast aggregation                   Disabled

AP ARP attack protection                   Enabled

AP multicast aggregation allowed VLANs     none

Console enable                             Enabled

AP Console Protection                      Disabled

AP Console Password                        ********

Password for Backup                        ********

AP USB Power override                      Disabled

RF Band for Backup                         all

Operation for Backup                       off

BLE Endpoint URL                           N/A

BLE Auth Token                             N/A

BLE Operation Mode                         Disabled

Health Check                               Disabled

Health Check Parameter                     mode ping packet-size 32 burst-size 5 report 60 frequency 10 retries 3

AirMatch Report Period                     5 minutes

AirMatch Measurement Duration              5 minutes

AirMatch Report Enabled                    Enabled

SAP MTU is used for the wired link of the AP. When this value is not configured, AP sends MTU discovery packet to negotiate the MTU between AP and controller which is also the path MTU. However, at default the SAP MTU value is considered to be 1500 bytes.

When it is configured, AP uses the configured SAP MTU, no more packets to do MTU discovery.

With the above-mentioned settings, the switch port with Aruba AP connected reports incremental Giant packets even though Jumbo is not enabled on switch, AP or controller.

Manually configuring the SAP MTU under ap system-profile of the Access point to 1500, resolves the issue.

If not, the AP tends to continuously do a MTU discovery which results in Giant Rx packets.