Airlink MP70 Cellular MTU

AirLink Routers AirLink routers
1

Hi there,

I don’t have any issue with fragmentation on other 4G products. They allow a full 1500 byte MTU into the cellular network, however I can’t find anywhere in the MP70 about where to set it. It seems like its statically set somewhere in the unit to 1302 bytes.

Does anyone know where I can change this?

Cheers,
Jordan.

2

Hi Jordan,
The MTU can be set in LAN -> DHCP/Addressing -> DHCP Options -> Set MTU to Auto or Manual.
You can refer in this document https://source.sierrawireless.com/resources/airlink/software_reference_docs/airlink-mp-series---configuration-guide/#sthash.aP7jtKhi.dpbs page 142

Thanks,

3

Thanks for the reply.

The issue I have is not to do with the MTU being set on the LAN side, but on the Cellular side.

Is there any way to set this?

4

In the log, it states this:

Jun 19 00:49:07 notice ALEOS_CONNECTMGMT: *** Network Connection successful. WAN IP [Cellular] : 10.XX.XX.XX
Jun 19 00:49:07 notice ALEOS_CONNECTMGMT: *** IP UP 10.XX.XX.XX : wwan0
Jun 19 00:49:07 notice ALEOS_CONNECTMGMT: Setting WWAN MTU size to 1358

Where can you set the WWAN MTU size?

5

Hi John,
The ALEOS user can not change the WAN MTU.
The decision on MTU size normally rests with the device that is creating the packet. Save for PAD mode packets, for which we do now have the ability to set the MTU, the gateways are not creating the packets. The host device is creating the packets, and we are simply passing them from the host device on to the cellular network. We do offer the ability through DHCP Options to tell the host device what its MTU should be, however. The onus for setting MTU is really on the device that is creating the packet. We take that responsibility for the PAD mode packets that we create, but other than that, the host device behind the gateway should be taking responsibility for the size of the packets it is creating and sending.

Thanks,

6

That is not correct. I can send a 1500 byte packet to the gateway’s LAN interface. Once that packet passes through the gateway it is fragmented, or if the df bit is set it’ll simply drop the packet. This means that in fact the device IS clamping the packet size at the WAN interface side.

Is there a way to access the shell of the device?

7

Hi jordan,
If the router on Cellular network sets MTU<1500, so this packet will be dropped.
If OpenVPN is enable for your device, you can set MTU for this tunnel.
Or if you are using Verizon, you can use Dynamic Mobile Network Routing (DMNR) feature on MP70, MTU is also set for this tunnel too; see more details in 41113545_ALEOS 4.13.0 Software Configuration User Guide for AirLink MP70_r1
If you want to access to shell of device, you can ssh to device with uasuser account (password is set in Admin->Change Password -> AFF user), port is set in Services -> Telnet/SSH
But user account does not have permission to change network interface.
If you need more detail support you should contact your Distributor.

Thanks,

8

Thank you for your assistance. I will give our distributor a go.

9

The solution to this, is to use the “Generic” radio firmware, not carrier based firmware. You’ll then need to factory reset the device. The MTU size is apparently a function of the radio firmware.