[Snap] VDSL connection and frame size

Forums › 2degrees (including Slingshot, Orcon, Flip, Stuff Fibre, MyRepublic, 2talk and Vocus) › [Snap] VDSL connection and frame size

spacedog

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#105576 7-Jul-2012 10:50

How does the authentication work on VDSL2 for SNAP? Is it a PPPOE type connection? Or a PPPOA? Or something entirely different?

I ask because I have a device that does not play nicely with the smaller frame size of PPPOE and I'm wondering what I'm in for if I switch over to VDSL2 with Snap?

sbiddle

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#652219 7-Jul-2012 12:11

No ISP uses PPPoA for VDSL2. For EUBA ISP's have the option of maintaining PPPoA for legacy fallback (and it's converted from PPPoA by the ISAM) or using any other method they choose - static IP's, DHCP or PPPoE.

spacedog

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#652222 7-Jul-2012 12:29

OK....so what is snap using? I have problems with my device when the MTU is down at 1492

vexxxboy

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#652223 7-Jul-2012 12:31

This is what Snap will tell you to use

PPPoE
VPI: 0
VCI: 110
Uses VLAN10

Common sense is not as common as you think.

spacedog

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#652225 7-Jul-2012 12:37

Damn....

PPPOE will break my VPN and boxee box functionality

:sadface:

deadlyllama

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#652228 7-Jul-2012 12:42

spacedog: Damn....

PPPOE will break my VPN and boxee box functionality

:sadface:

It doesn't have to -- just drop the MTU on your VPN a bit (by 8 bytes?). TCP PMTU discovery should fix everything for you.

spacedog

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#652230 7-Jul-2012 12:47

deadlyllama:
spacedog: Damn....

PPPOE will break my VPN and boxee box functionality

:sadface:

It doesn't have to -- just drop the MTU on your VPN a bit (by 8 bytes?). TCP PMTU discovery should fix everything for you.

Sadly, the boxee box is locked down so you can't control the MTU on it's built-in VPN client...Lame...yes, but I've been waiting for them to fix it for 6 months now...so I have to work around that.

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sbiddle

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#652233 7-Jul-2012 12:55

EUBA supports 1500 byte MTU's, but since most ISP's use PPPoE for simplicity you're stuck with 1492 on PPPoE. If you had a static or dynamic IP you could have 1500.

mercutio

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#652475 8-Jul-2012 11:32

sbiddle: EUBA supports 1500 byte MTU's, but since most ISP's use PPPoE for simplicity you're stuck with 1492 on PPPoE. If you had a static or dynamic IP you could have 1500.

Isn't http://tools.ietf.org/html/rfc4638 meant to fix that?

I happened to have problems with 1492 byte mtus, mostly with something using UDP, I found TP-Link 8960 modem could not set a 1500 byte MTU on pppoa connections unless you telnetted in, and set it with ifconfig and deleted the mss clamping rules. Ended up emailing them. They did fix it in the end.

http://www.tp-link.com/en/support/download/?model=TD-W8960N&version=V3#tbl_j

spacedog

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#652572 8-Jul-2012 17:58

mercutio:
sbiddle: EUBA supports 1500 byte MTU's, but since most ISP's use PPPoE for simplicity you're stuck with 1492 on PPPoE. If you had a static or dynamic IP you could have 1500.

Isn't http://tools.ietf.org/html/rfc4638 meant to fix that?

I happened to have problems with 1492 byte mtus, mostly with something using UDP, I found TP-Link 8960 modem could not set a 1500 byte MTU on pppoa connections unless you telnetted in, and set it with ifconfig and deleted the mss clamping rules. Ended up emailing them. They did fix it in the end.

http://www.tp-link.com/en/support/download/?model=TD-W8960N&version=V3#tbl_j

You said PPPOA and the tp-link firmware fixes it for PPPOA.

The issue I'm discussing is with PPPOE which is pretty much capped at 1492. The IETF article you reference is all well and good for theory, but it is not always put in practice.

The specific issue I have is that my stoopid boxee box has a built-in VPN client and that client *ALWAYS* negotiates at 1500. However, when I'm connected via PPPOE the 1492 MTU causes fragmentation with the VPNs 1500 MTU and eventually the connection falls over. When I'm connected on a PPPOA connection, it manages to work OK. It's definitely a stupid bug in my device, but it's a bug that I have to workaround unfortunately. Not anyone's fault except the people at boxee, tbqh.

mercutio

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#652577 8-Jul-2012 18:14

spacedog:
mercutio:
sbiddle: EUBA supports 1500 byte MTU's, but since most ISP's use PPPoE for simplicity you're stuck with 1492 on PPPoE. If you had a static or dynamic IP you could have 1500.

Isn't http://tools.ietf.org/html/rfc4638 meant to fix that?

I happened to have problems with 1492 byte mtus, mostly with something using UDP, I found TP-Link 8960 modem could not set a 1500 byte MTU on pppoa connections unless you telnetted in, and set it with ifconfig and deleted the mss clamping rules. Ended up emailing them. They did fix it in the end.

http://www.tp-link.com/en/support/download/?model=TD-W8960N&version=V3#tbl_j

You said PPPOA and the tp-link firmware fixes it for PPPOA.

The issue I'm discussing is with PPPOE which is pretty much capped at 1492. The IETF article you reference is all well and good for theory, but it is not always put in practice.

Yeh, doing a bit of research some clients have only recently implemented that feature, but you have flexibility with clients. I'm not sure if the server supports it...

The specific issue I have is that my stoopid boxee box has a built-in VPN client and that client *ALWAYS* negotiates at 1500. However, when I'm connected via PPPOE the 1492 MTU causes fragmentation with the VPNs 1500 MTU and eventually the connection falls over. When I'm connected on a PPPOA connection, it manages to work OK. It's definitely a stupid bug in my device, but it's a bug that I have to workaround unfortunately. Not anyone's fault except the people at boxee, tbqh.

From a quick Google search it looks like the remote VPN should be able to negotiate a lower mtu.

PenultimateHop

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#652596 8-Jul-2012 19:00

sbiddle: EUBA supports 1500 byte MTU's, but since most ISP's use PPPoE for simplicity you're stuck with 1492 on PPPoE. If you had a static or dynamic IP you could have 1500.

EUBA supports 1500 byte PPPoE MTUs, and the ISAM will even negotiate RFC4638 support when operating as an oA to oE interworking function.

Many poorly designed CPEs do not support it; or your ISP's BRAS is misconfigured.