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Standard User rlees85
(newbie) Mon 09-Oct-17 14:02:52
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Zen and RFC 4638 Baby Jumbo Frames


[link to this post]
 
Sadly, Zen has dropped support for RFC 4638 as of a week or so ago.

I know this for sure on ADSL, not too sure about Fibre.

I had an email from Zen confirming there will be an "upgrade" and as such my internet may wobble for a bit about a couple of weeks ago, since then my router will not use RFC 4638. Setting it by force causes packet loss.

Called Zen's technical team earlier and confirmed they have dropped RFC 4638.

No idea why they would downgrade their service in this way. I asked if they would ever switch it back on and they said no.

Shame...

I am posting this to stop anyone spending hours messing with OpenWRT wondering why they can't get this functionality working. Its them, not you wink
Standard User BatBoy
(sensei) Mon 09-Oct-17 14:10:13
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
Is this on Zens own backhaul only or also on BT?
Standard User Ixel
(member) Mon 09-Oct-17 14:18:04
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
Interesting, I don't currently use baby jumbo frames but I had considered trying it out as I imagine my EdgeRouter would do this if I wanted it to (via HG612). If FTTC also has lost this (via Zen's back-haul) then I won't be ever trying that for the remainder of the contract term.


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ISP Representative jongreen84
(isp) Mon 09-Oct-17 19:33:56
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
Hi,

I don't post here too often as my colleague Andy has been picking things up - but I've just noticed this thread. I'll take a look into this and post back.

Cheers,

Jon
The above post has been made by an ISP REPRESENTATIVE (although not necessarily the ISP being discussed in the post).
Standard User legume
(experienced) Mon 09-Oct-17 23:30:14
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
In reply to a post by rlees85:
Sadly, Zen has dropped support for RFC 4638 as of a week or so ago.

I know this for sure on ADSL, not too sure about Fibre.


I guess if you need passthrough from something pretending to be a modem or Zen are "special" for ADSL then fair enough, but ...

Why would anyone in normal setups be using pppoe(oa) on adsl anyway.
pppoa vcmux is more efficient and should be OK at 1500 MTU without anything special needed.

Edit: Though with adsl pppoe vc mux running 1478 MTU or MSS clamp is slightly more efficient than 1500.

Edited by legume (Mon 09-Oct-17 23:42:10)

Standard User rlees85
(newbie) Tue 10-Oct-17 10:04:34
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
It is using BTs backhaul, be great of Zen do change their mind...

I'm not an expert in MSS/Clamping but I am sure that PPPoA is supposed to be even more inefficient than PPPoE with standard 1492.
Standard User legume
(experienced) Tue 10-Oct-17 11:19:48
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
In reply to a post by rlees85:
It is using BTs backhaul, be great of Zen do change their mind...

I'm not an expert in MSS/Clamping but I am sure that PPPoA is supposed to be even more inefficient than PPPoE with standard 1492.

MSS clamping is a bit OTT unless you know iptables. If you are using a MTU < 1500 your router will probably do it for you.

On ADSL pppoe isn't just pppoe as it is on FTTC, it's still got to go over aal5 and ATM which means it's at least 22 bytes per packet more fixed overhead than pppoa vc multiplex.
Depending on packet size there will be some additional variation for both as AAL5 pads out to fit a whole number of ATM cells, but for ADSL it is less efficient.
Standard User rlees85
(newbie) Wed 11-Oct-17 16:50:37
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: legume] [link to this post]
 
Interesting.... ISPs and BT are never that forthcoming with technical details like that. Last time I checked people seemed to recommend PPPoE even on ADSL connections but after another look around it seems you are right and generally all ADSL stuff goes over ATM anyway.... thanks for the info

Are you sure your information applies to 21CN?

The 21CN network was built from the start to support PPPoE and this is actually the preferred connection method but they also detect and support any PPPoA connections for backwards compatibility.

Edited by rlees85 (Wed 11-Oct-17 16:51:55)

Standard User legume
(experienced) Wed 11-Oct-17 21:22:04
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
Source for quote?

I guess there is scope for confusion, but AFAIK 21cn is ethernet based teleco side and 20cn was ATM further into their network.

For ADSL even on 21cn your modem is still using ATM till it gets to the exchange, so pppoe in that case is pppoeoa = more overhead than pppoa.

For VDSL modems on FTTC there is no ATM, it's PTM which is a bit more efficient for "on the wire" overheads.
Standard User legume
(experienced) Wed 11-Oct-17 22:15:37
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: legume] [link to this post]
 
FWIW BT do go into some detail, you just need to know where to look =

http://www.sinet.bt.com/sinet/SINs/pdf/472v2p8.pdf

Top of page 13 -

"It should be noted that the use of LLC/SNAP and PPPoE incur a higher protocol overhead and
therefore will provide a lower throughput than the use of PPPoA/VC-mux."

As it says on page 12 that pppoe is llc/snap my previous extra overhead figure is now increased by 8.
Standard User rlees85
(newbie) Sat 14-Oct-17 11:45:39
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: legume] [link to this post]
 
Again good information, thanks... I think as my modem and router are separate I am stuck with PPPoE(oA) though!
Standard User jbuk__
(newbie) Thu 09-Nov-17 21:37:03
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Re: Zen and RFC 4638 Baby Jumbo Frames


[re: rlees85] [link to this post]
 
FWIW I have just set up a Cisco 887VA on my GEA FTTC line with Zen and with no special configuration on my part I am successfully getting 1500 MTU, confirmed by https://www.speedguide.net/analyzer.php
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