What is Maximum Transmission Unit (MTU) size allowed for network transmissions using GRE , IPsec and xSec ?
This article applies to Aruba Mobility Controllers running ArubaOS version 18.104.22.168.
The maximum transmission unit (MTU) for GRE tunnel between Aruba Controller and Access Points
For AP-104/105, AP-92/93/93H, AP68(P), AP-175 the default MTU for the GRE tunnel is 1500 bytes and 1200 bytes for the RAP3, RAP-5 , RAP-108/109
Whereas Aruba APs AP-114/115 , AP-224/225 , AP-12x, AP-13x and RAP-155(P) doesn’t take the default instead they use an MTU discovery mechanism to set an appropriate MTU for the GRE tunnel used for carrying encrypted user traffic and GRE heartbeats
Also the MTU can be explicitly set in the AP system profile to a value in the range of 1024-1578. If the MTU is explicitly set, the GRE tunnel MTU is the value specified in the system profile and the MTU discovery mechanism is not used. We can use the extended ping functionality found in AOS 6.3 or Higher to find the MTU size of the network between the controller and the AP.
when you are dealing with a noisy channel or when there occur more network errors, you can try decreasing the MTU. as an insight, if the noise destroys a "big" packet, there will be more to retransmit than if the packet was small and If the network is burdened with unnecessary overhead, packets may be too small then try increasing the MTU.
The maximum transmission unit (MTU) for GRE tunnel between Aruba controllers or another vendor’s router
The range of allowed values is1024-1500, default is 1100 bytes
The maximum transmission unit (MTU) for frames using the IPSEC protocol ( Aruba RAP's )
The range of allowed values is1024-1500, default is 1500 bytes
The maximum transmission unit (MTU) for frames using the xSec protocol.
The range of allowed values is 1024-1500 bytes, default is1300 bytes