Good cheap router capable of 1508 byte mini jumbo frames on ethernet?

Hi All,
I'm running a number of BT Homehubs (2a, 2b, 5a).
Although I really like the hhv5a for LEDE, the lantiq ethernet drivers do not allow ethernet frames > 1500, and I want to use a LEDE based router to run against a huawai HG8240 GPON using PPPoE with mini-jumbo frames of 1508 bytes, so that I get the full 1500 mtu to the internet on a BT FTTP/FTTH fibre connection.

Does anyone have a concrete recommendation for a cheap router with 2 or more wired ethernet ports which can support mini-jumbo frames on (at least one of the) ethernet ports; or even just a recommendation on chipset with driver support for this purpose?


on any gigabit router you should have possibility to set 1508 MTU, search the ToH list for gigabit supported routers, tl 1043wd is quite cheap, but depends what speeds do you need, for the moment it can't do wirespeed (gigabit routing) on LEDE

The huawai HG8240 looks like its don't allow more then 1500 mtu on the lan port.
but i am not 100% sure. Just looked on the service manual.

It's so difficult to find information on this topic - e.g. my fttc connection had a BT VDSL modem - reports indicated it should support 1508, but when I eventually retired it, opened and accessed the serial, I found it to have the same lantiq chipset and limited drivers as the bthhv5... so limited to 1500 on the wire (BT 'ECI b-focus V-2Fub/r Rev.B').
Are there any hints that BT can configure the HG8240 for some other mode to get the full 1500 byte packets (e.g. just as a router)? I beleive it's fairly locked down from user access, as I think it's the point where the bitrate limiting is done - they don't want individual customers enabling the fill 330mbits!
The FTTH connection is in my business partner's premises - I'll try to test the HG8240 at 1508 from a laptop if possible.

Mmh, that is a GPON ONT device? In that case yes, it is involved in bitrate limiting (by honoring the transmit time slots assigned from the OLT). As far as I can a specification conformingt ONT will never allow the local user to exceed the transmit grants from the OLT as that would lead to collisions on the fiber that would ruin the experience for all users sharing the same fiber. I guess in theory one could parse the grant map to find the empty slots and try to use those, but I am not sure whether the OLT will actually accept packets sent without an explicit grant...


OK, success!.

We installed a USB gigabit ethernet adaptor on the BTHHV5 LEDE router.

Test Successful; with the gigabit ethernet set to an MTU of 2000, and the PPPoE on LEDE set to 1508, we're getting the full 1500 bytes to the internet via the HG8240 on BT Business FTTH/FTTP. We also see an IPV6 address (but not exactly sure how to interpret this)...

Just to be absolutely clear.
Huawei HG8240 connected to fibre (UK BT Business near IP14; debenham exchange).
BT Homehub 5 Type A with LEDE 17.01.3 installed.
USB gigabit ethernet (ASIX) plugged into the LEDE router with driver installed, connected to HG8240.
PPPoE using the BT business username and password as given in connection email.
All working at MTU of 1500 (i.e. ethernet at 1508 between LEDE and HG8240).

Happy day :).

There is no need to use an external modem, or a USB gigabit NIC to get baby jumbo frames for VDSL PPPoE on the HH5a, snippets from my /etc/config/network ...

config dsl 'dsl'
option xfer_mode 'ptm'
option annex 'b'
option line_mode 'vdsl'

config device 'wan_dev'
option macaddr 'xx:xx:xx:xx:xx:xx'
option mtu '1508'
option name 'dsl0'

config interface 'WAN1'
option proto 'pppoe'
option username ''
option password 'xxxxxx'
option ipv6 'auto'
option delegate '0'
option mtu '1508'
option ifname 'dsl0.101'

Results verified with MTU Test as giving 1500 byte MTU

If you carefully re-read the first post, you will notice that the challenge was to use MTU 1508 on one of the ethernet interfaces...

Sorry, I saw the 1508 and jumped to the conclusion it was the "usual" problem of baby jumbo on the DSL interface...

:). Am happy to say I even forgot there was a usb to ethernet involved... It's just been working on a remote site since I posted....