[RP-PPPoE] Choosing an access concentrator

[Mike]

Rudolf Meijering wrote:
> I suppose the pppoe packet contains the ethernet mac address from the
> adsl modem, so I would have to choose between packets with ebtables.
>
>   
Ahh, now I think I understand what you are trying to do.

You have 2 adsl modems/lines connecting to the same provider and you 
want to try and do load balanceing of sorts by using both at the same 
time, yes?

One strategy is to simply have multiple nics in the machine, with one 
adsl modem per nic. Then you could specify by interface such as 
'nic-eth0' and 'nic-eth1' for example. Trying to do it without multiple 
nics (like, having the modems on a switch) is highly likely to be fail. 
Why? Most ADSL access concentrators will 'learn' a subscriber mac 
address as being behind some port, and then it locks it into it's mac 
tables. This works to secure the adsl network against monkey business 
and help thawart one subscriber port from being able to monkey with 
another. Even if the access concentrator isn't locking mac addresses in 
it's table, you'll still have the general problem of pppoe discovery 
forwarding discovery frames down both modems (since they'd be on the 
same broadcast domain), but the replies are only going to come back over 
one of them. This is because the access concentrator is acting like a 
switch - it's only going to send reply packets back to your source mac 
address over 1 port and 1 port only (eg: the last one it learned your 
mac address was on). You could perhaps try using an 802.1q vlan enabled 
switch, putting each port in a seperate vlan, and creating vlan 
interfaces on your machine with different mac addresses as well. Seems 
like a bit of work however.

    Assuming you get to the point of having multiple dsl modems, then 
what? Each ppp link will have a separate ip address and it's possible to 
do ip nat so that some outbound connections go over 1 link and the rest 
over another. If however your provider has assigned you a subnet, then 
you may get per packet load balancing if their equipment sees your 
subnet over both links. This is default behavior for cisco (subject to 
'maximum-paths' config parameter). There's additional work you would 
then do on your side which I have never done myself and can't speak to.


-ILC