I was wondering if is possible to configure a router subinterface to authenticate with an ISP DSL modem. I tried to configure the interface with the command "pppoe enable" but I'm receiving the following message:
PPPoE create bba subblock failed.
I do not know if the this output is because the Interface is actually a sub-interface (Fa0.10) or maybe I forgot to enable something else.
Are you talking about 802.1X or 802.1Q? It appears that you want to discuss 802.1Q subinterfaces and PPPoE running on them.
Configuring PPPoE clients/servers on 802.1Q subinterfaces should work just fine. Perhaps you could post your current running-config and also a transcript of the session where you try to configure the PPPoE and the error message appears. The larger context will hopefully provide more information to see what is the problem.
Often some feature do not work on sub-interfaces.
For pppoe-client that is not too bad because it can co-exist with an regular IP address on the main itnerface.
True. I am sure that several IOSes support the PPPoE Client on 802.1Q subinterfaces. However, I recall that this feature was not universally available. Perhaps Jose could tell use the type of his device and the IOS version.