Broadband Related > FTTC and FTTP Issues

pppoe discovery

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bilbokitz:
Thanks for the replies, I will add "passive" to see what happens next time.

Extended period being - not sure of the exact amount but I leave it an hour when testing to be sure. The router can be unplugged for a few minutes and connect again.


--- Quote ---Surely the PPP session won't still be alive if the router has been power cycled. The router must surely go through the whole PPPoE discovery process again, before then starting a new PPP session.
--- End quote ---

I read on this site that the ppp session can survive a while hence my presumption


--- Quote --- "primary partner MAC"   In which case... are there some L2 protocols that you need to turn off?
--- End quote ---

I will have to look this primary partner thing up but it sounds plausible.


--- Quote ---How exactly do you see that the PADI hits the modem?
--- End quote ---

I ran tcpdump on the prtm0 interface of the modem DGA4130 and looked at the file in wireshark. I also ran wireshark on the port (mirrored) of the port connected to the modem as well as the port connected to the router, they all matched up. I also have a hg612 but I am fairly sure the same happens I will have to double check that.


--- Quote ---How do the router & modem behave if there is no VLAN, and they are connected into a single plain switch? Or network of switches?
--- End quote ---
More testing to do - the kids will love me


ps I do see broadcasts from the tplink switches in the capture, when looked up the protocol has something to so with the way the switches communicate with the tplink configuration utility.

WWWombat:

--- Quote from: bilbokitz on December 12, 2017, 11:47:48 AM ---I read on this site that the ppp session can survive a while hence my presumption

--- End quote ---

I think that's the other way around - the PPP session survives when the router stays powered up, but the modem goes down (power or resync).


--- Quote from: bilbokitz on December 12, 2017, 11:47:48 AM ---I will have to look this primary partner thing up but it sounds plausible.

--- End quote ---

You won't find anything - that terminology is made up, because I can't think of a "proper" way to describe this.

In Cisco switches, once of the security features is to make a port "sticky". It doesn't care what MAC address is used for a device connected to a port, but once one MAC address is used, then the port will accept no other address. All other frames will be discarded.

If your modem has a similar restriction, then it might lock out the "second" device, no matter that the first device is just the switch sending out dumb management broadcasts. And, because the designer of the cheap modem might expect that the modem is always directly connected to the router, they might have made a shortcut that ends up working like this.


--- Quote from: bilbokitz on December 12, 2017, 11:47:48 AM ---I ran tcpdump on the prtm0 interface of the modem DGA4130 and looked at the file in wireshark. I also ran wireshark on the port (mirrored) of the port connected to the modem as well as the port connected to the router, they all matched up.

--- End quote ---

Yeah, that sounds comprehensive enough.


--- Quote from: bilbokitz on December 12, 2017, 11:47:48 AM ---ps I do see broadcasts from the tplink switches in the capture, when looked up the protocol has something to so with the way the switches communicate with the tplink configuration utility.

--- End quote ---

If my theory is right, then at least you're seeing the packets from the switch that could trigger that behaviour.

niemand:
So most things with a modem mode will cache the first MAC address they see and that's all they'll talk to. They have an ARP table with a single entry on the LAN side.

This is probably what's happening to you here as mentioned earlier. There's nothing arcane about PPP particularly, but modems will only learn a single MAC address usually, for obvious reasons - a modem is breaking out traffic from a different protocol that doesn't have any layer 2/3 addressing the modem can use. It doesn't have an IP address to distinguish between destinations, it doesn't even have the luxury of being able to use PPPoE as some providers don't, so needs either some code to snoop traffic and bind a PPP / IPoE / whatever session to the MAC address that initiated it or a simple bind to first MAC address it sees.

Guess which one gets used?  :)

bilbokitz:
Sounds like were onto a winner just need to figure out how to stop the tplink broadcasting. It looks like there are inherent problems with these easy smart switches.

Can we do a manual bind?  What is the mechanism, like an arp entry?

edit: I think it is a setting called loop detection that has been causing the broadcast as I have switched it off and can no longer detect the broadcast. Now to test when I can switch off the internet.

WWWombat:
Loop detection is probably a variant of the spanning tree protocol (STP).

It is used when you deliberately create multiple connections to other switches (loops) for redundancy reasons. STP then blocks the excess connections, leaving them as a standby ready for tailored. Great for enterprise networks. Not so useful here.

It is indeed one of the first packets sent by the switch when a connection is made (is when cable is plugged in).

Are there any other settings to turn on/off?

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