cancel
Showing results for 
Show  only  | Search instead for 
Did you mean: 
simon_h
Beginner
5,748 Views
Message 1 of 9

MTU 1500 on FTTP/FTTH

Is it possible to get a configuration on the HG8240 where the MTU of the internet connection is the full 1500 bytes?

From the documentation on the HG8240, it looks like it can do this, but not with pppoe, and only if the carrier configures it; will BT do this for us, e.g. configure it to bridge mode?

Is this availabl on domestic connection, or only on a business connection?

Happy to use a different router than the present HH5....

s

0 Ratings
8 REPLIES 8
jonS
Aspiring Contributor
5,664 Views
Message 2 of 9

Re: MTU 1500 on FTTP/FTTH

baby jumbo frames RFC4638 seem to work fine. I set my router to use a pppoe connection with 1508 MTU and a 1500 MTU on the port. I can then ping out with don't fragment just fine with 1472 bytes.

0 Ratings
simon_h
Beginner
5,523 Views
Message 3 of 9

Re: MTU 1500 on FTTP/FTTH

@jonS - what router did you use?  I'm looking for one which supports 1508 with OpenWRT/LEDE, but not sure how to determine support.  Have been told 'any gigabit router', but I run BTHHV5 with LEDE and the lantiq network drivers don't do mini-jumbo, so anything lantiq based is currently off the table.

s

0 Ratings
jonS
Aspiring Contributor
5,494 Views
Message 4 of 9

Re: MTU 1500 on FTTP/FTTH

I have been using an ubiquiti edge router:

https://www.ubnt.com/products/#edgemax

They are based on the vyatta code base.
0 Ratings
simon_h
Beginner
5,480 Views
Message 5 of 9

Re: MTU 1500 on FTTP/FTTH

thanks jon,

I've gone for a usb gigabit adaptor on my LEDE bthhv5; seems to have the MTU required - hope to test later today with the GPON.  If all works fine, will look at either fixing the ethernet in LEDE or a different router - or just put together two hhv5s with gigabit adaptors as main and cold spare.

s

0 Ratings
jonS
Aspiring Contributor
5,433 Views
Message 6 of 9

Re: MTU 1500 on FTTP/FTTH

Sounds like a lot of effort 😄 Plus also I wanted something that was rack mountable, without any wifi built in.

0 Ratings
simon_h
Beginner
5,424 Views
Message 7 of 9

Re: MTU 1500 on FTTP/FTTH

🙂 Tested & working with the USB adaptor; perfect 1500 all the way through!

 

Maybe when we get more traffic, I'll think about something more prefessional...

Now just got to work out how to get IPV6 working (should be enabled by BT), and why BT are limiting to 36Mbits down, when thier minimum package seems to be 74.  And probably secure that USB adaptor with gaffer tape....

 

But hopefully its useful for anyone else who has LEDE/OpenWRT on a device which does not do > 1500 on the ethernet (basically, anything Lantiq based) to know that they can do 1508 with a USB adaptor, push come to shove....

 

0 Ratings
jonS
Aspiring Contributor
5,408 Views
Message 8 of 9

Re: MTU 1500 on FTTP/FTTH

Sounds good.

 

ipv6 works fine using dhcpv6 pd slaac with a pd of /56

0 Ratings
ameeno
Aspiring Contributor
4,403 Views
Message 9 of 9

Re: MTU 1500 on FTTP/FTTH

Hello.

 

Maybe I am late to the party and the network has changed since this thread.

 

My BT 330/50 Ultrafast fttp was enabled yesterday. I have made some discoveries RE: ipv6 and MTU 1500.

 

I was able to succsessfully have IPV6 using pd 56 and a dhcp cliuent enabled on my router, then use slaac to distribute ipv6 addresses to my bridged lan devices.

 

In order for me to get  a full 1500 MTU over the PPPOE bt connection, i had to first increase my ethernet1 interface mtu to 1520 (jumbo frames) to allow the pppoe connection to carry mtu 1500.

 

 

I suppose it is logical really, the default setting for ethernet ports MTU is 1500. the pppoe connection rides *INSIDE* the ethernet connection, and so the frame size must be reduced to prevent fragmentation.

 

 

so before increasing the MTU of the pppoe connection to mtu 1500, we must first widen the max frame size of our eth1 WAN ethernet port to carry those frames, as the pppoe frames have to have headers attached for authentication purposes.

 

**PS this setup is for an Ethernet to the Openreach ftth NTU, not the VDSL, but i Suspect the same logic would apply to a VDSL connection. jumbro frames must be supported on the interface to at least 1520 to have 1500 MTU over the interface embedded pppoe connection**

0 Ratings