Recent posts

#1

IDNet Help / Re: Openreach Fibre PPPoE MTU ...

Last post by nowster - Yesterday at 16:09:22

If the kit at both ends supports Path MTU Discovery, there's no fragmentation.

#2

IDNet Help / Re: Internet down?

Last post by peasblossom - Yesterday at 06:14:45

As I can see the green cabinet, I know there are no Openreach engineers loitering round it. My thought in the first post was there might be wider work going on, not just local stuff.

#3

IDNet Help / Re: Internet down?

Last post by Simon - Apr 28, 2025, 22:06:58

In past experience, they don't always tell the ISPs if they're just working on a local cabinet. I'm not saying this is the problem, just that it's a possibility.

#4

IDNet Help / Re: Openreach Fibre PPPoE MTU ...

Last post by njh - Apr 28, 2025, 22:06:26

Yeah, 1492 is the default. I guess there isn't an automatic way of knowing if Ethernet between the ONT and your router supports Baby Jumbos / RFC4638.

I believe using a PPPoE MTU of 1500 improves performance by matching the standard 1500-byte MTU of most networks. Standard PPPoE typically forces a smaller 1492-byte MTU, causing fragmentation of larger packets, which are common on LANs.

No fragmentation means less processing for the routers - so I think it is worth giving it a go.

#5

IDNet Help / Re: Internet down?

Last post by peasblossom - Apr 28, 2025, 21:39:34

I didn't ask specifically about that but I assumed Will's comment that there didn't appear to be any issues covered it.

#6

IDNet Help / Re: Internet down?

Last post by Simon - Apr 28, 2025, 20:29:46

Any Openreach work going on in the locality?

#7

IDNet Help / Re: Internet down?

Last post by peasblossom - Apr 28, 2025, 18:57:42

It feel over again this afternoon (for nearly 90 mins - I was out) so I rang IDNet. Will tapped away on a keyboard, I rebooted the router. Will couldn't see any issues.

#8

IDNet Help / Re: Openreach Fibre PPPoE MTU ...

Last post by nowster - Apr 28, 2025, 16:49:33

Ours seems to have negotiated 1492:

Code Select Expand

13: ppp0: <POINTOPOINT,MULTICAST,NOARP,UP,LOWER_UP> mtu 1492 qdisc pfifo_fast state UNKNOWN mode DEFAULT group default qlen 3

#9

IDNet Help / Openreach Fibre PPPoE MTU of 1...

Last post by njh - Apr 27, 2025, 19:14:59

Is having a PPPoE MTU of 1500 (and Ethernet MTU of 1508 to the ONT) well supported these days on Openreach FTTP? Any gotchas?

I think it tried it years ago on DSL but ran into problems...

Thanks!

#10

IDNet Help / Re: Internet down?

Last post by nowster - Apr 26, 2025, 15:35:08

I've had PPPoE give a 10.100.xx.xx address to the router recently after midnight. Restarting the link gave the correct address.