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Author Topic: PPPoA PPPoE  (Read 5369 times)

cooperfarncombe

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PPPoA PPPoE
« on: January 22, 2009, 11:17:29 PM »

Hi,

I am new to this excellent site and forum. 

I have seen a past thread that recommends routers are set to PPPoA and until recently my router /modem was set to PPPoA.  However after upgrading the router / modem firmware I found that the only way I could get a connection to work for all sites was to select PPPoE.  Some sites (e.g. Google) loaded OK but others (ebay, BBC) were so slow that they timed-out.

The router modem is a Belkin F5D7633-4 and my ISP is Orange over a LLU circuit.  Does anyone know why in these circumstances I need PPPoE?

David
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kitz

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Re: PPPoA PPPoE
« Reply #1 on: January 22, 2009, 11:28:07 PM »

Hi and welcome

>> Does anyone know why in these circumstances I need PPPoE?

No sorry I dont.   The backhaul from the exchange is ATM hence the need for PPPoA. 
Some exchanges/equipment will emulate PPPoE, but its actually PPPoEoA and therefore carries additional overheads.

>> but others (ebay, BBC) were so slow that they timed-out.

That actually sounds like an MTU problem.  In fact its actually quite common on Orange - so much so that orangeproblems have actually asked permission to copy my MTU settings page.
Try MTU of 1430.





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kitz

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Re: PPPoA PPPoE
« Reply #2 on: January 22, 2009, 11:38:16 PM »

Its just dawned why PPPoE is likely working  :doh:
 - the additional overheads in PPPoEoA will mean less actual useful data in the packet.. therefore it will have the effect of reducing the MSS once data is off the ATM backhaul. The smaller packets will therefore get through and wont be blackholed.
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cooperfarncombe

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Re: PPPoA PPPoE
« Reply #3 on: January 25, 2009, 11:19:10 AM »

Thanks for the info Kitz. 

I understand what you are saying and have tried to alter the MTU setting.  However, on this particular modem (Belkin F5D7633-4) it does not seem to change!  Changing the setting using the Belkin utility does not seem to actually change the MTU setting as verified using the  "ping -f -l [packet size]" method.  It seems to be stuck at 1472.  I put this down to the Belkin modem. 

I found that PPPoE works by accident - a desperate attempt to see if I could alter the MTU with PPPoE selected rather than PPPoA.

The PPPoEoA  additional overheads could be the answer or the the only thing that I can think of is that although I apparently have PPPoE selected it is actually PPPoA and the set-up utility is labelled wrong.

This all happened after upgrading the firmware (Belkin F5D7633-4) from the original version (Verion V1.00.00, I think) to Version V1.00.25.  On the original version I had PPPoA selected and everything worked fine.

Since it works I will leave as is - but this info may help others if they come across this particular modem.

David



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kitz

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Re: PPPoA PPPoE
« Reply #4 on: January 25, 2009, 12:54:10 PM »

Thanks for the feedback. 

Have you tried setting the MTU on the local machine? 
Path MTUD is end to end, therefore if the MTU is lower at any point during transit, then this becomes a black hole.

One other thing that can also 'break the Internet' to some sites is if the router has got ICMP ping turned off (the router isnt pingable).
ICMP is a valid internet protocol and turning off ICMP stops Path MTU Discovery from working.

>> This all happened after upgrading the firmware (Belkin F5D7633-4)

I wonder if the new firmware is set to disable ping by default
- if so and if the MTU on the local machine is more than any where on the orange network... then if you request any data from secure sites whose server isnt set up to respond to ICMP..  then that site will be black-holed.

In these cases making the router pingable solves the problem.
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