@lleachii Even if I intended to break the "terms of service" I signed with my ISP, which I don't, I wouldn't be breaking the forum guidelines for discussing it; the forum guidelines state "breaking any other law" and the terms of service of a contract are not law. If I broke the ToS of my contract, my ISP could cancel it, but they could not bring me to court unless they could prove I broke the actual laws of my country.
You are making it hard to follow the thread and for me to be assisted with my issue. I ask of you that you please stop posting nonsense.
I disagree with your idea, but OK. As was noted, malicious intent is usually involved; but I guess people didn't realize - I'm not the one who said that.
I disagree it's nonsense; and apologize if you cannot follow the real concern. But I am now able to assist.
Now to your question - can you explain why the second IP doesn't have to connect to the Internet.
This is necessary to assist with telling you how to assign the IP.
It provides the necessary code to establish common (W)WAN connectivity, just what you are wanting to achieve appears a bit off the common frame, that is if you want indeed to set a static publicly routable IP address and change its gateway.
Indeed, iproute2 is a pretty comprehensive toolset for such tasks.
Otherwise you may also look into the ppp package that provides the PPP daemon and what can be done with it.
The network manager script that sets parameters for the ppp client is located at /lib/netifd/ppp-up and might be some starting point.
I am afraid I have not fiddled with that and would not be able to provide further insight but maybe someone else does.
I thought of altering that script when I thought the OP said they did it before. My other suggestion is depending on details, enumerating it as an @ - as I'm certain a second <interface> in the OpenWrt list will not work for PPPoE.
Then...I realized this wasn't backed by the OP with information...it was only asserted that the OP knew nothing technically deterred them...
Then I saw that the series of relevant of RFCs that @mikma posted - say otherwise. I read them...
You cannot alter the IP address on the connection (i.e. the packet stream), especially if it's encrypted.
EDIT: I'm trying hard to see if this is a clarification only for wireless, but I see nothing else that overrides the protocol or re-explains it for any other medium. DSL is closed circuit RF in that sense tho...
This question has not been answered yet.
Since your hesitation to explain your intentions or your goal makes the forum users assume the wildest things, I suggest you first provide some explanation.
This helps forum users to better understand the problem and to provide better answers.
Perhaps I can help point this VERY IMPORTANT question in a good direction:
PPPoE is no longer "only dynamic."
CenturyLink (aka Lumen) is a reasonably big ISP, with about 5% of the US market: over 5 million customers. I use their gigabit fiber service.
They sell low cost static IP's for those who need them (eg we have a published domain name and some servers.)
That service is provided via PPPoE with a VLAN tag (201). Plug in the cat 6 ethernet cable, configure your WAN VLAN and PPPoE settings, and you're good to go.
The simple answer is: in the simple case, a static IP is automatically supported, because it is downloaded from the ISP as part of the PPPoE handshake.
The more complex answer is: OpenWRT and other such software absolutely needs to provide for static IP with PPPoE. In various situations it is important to know this, and even to configure the static IP into the software. For example, HA failover.