Giant packets on switch port connected to Access point
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.