Hello Kamil,
I apologize for answering so lately.
1. Are there any known security implications of such a configuration - IPv6 auto-config in ISP environment? I would assume that since this is a layer 2 "pipe" with SVI on the top, IPv6 addresses will be traversing only along this "pipe" towards client's network...
Please take my answer here with a grain of salt as I do not work in an ISP environment.
From the perspective of the ISP alone, there are no obvious security issues related to client IPv6 address autoconfiguration because you as an ISP do not use it yourself, you just offer this service to a client. That means that you cannot be influenced by whatever setting the client chooses, nor should you be affected by any client router also offering IPv6 autoconfig service. In fact, it is very probable that you are already allowing the client to use IPv6 autoconfig because the default setting on Cisco routers is to send the Router Advertisements as soon as the IPv6 routing is configured and the interface is assigned an IPv6 address.
2. I would expect the end customer to have IPv6 auto-configuration inside their enterprise
Not necessarily. The IPv6 autoconfig is a per-link feature, meaning that each interface of a router can offer (or decline to offer) this functionality individually and independently of other interfaces. If you offer IPv6 autoconfig to your client, you are only offering this functionality to client's devices directly attached to your own router. If the client has another router, networks behind it are not using your IPv6 autoconfig services but rather that router's services.
3. Is it an appropriate and recommended methodology to deploy IPv6 auto-configuration in ISP scenarios?
I do not feel qualified to authoritatively answer this question. In general, however, the connection between an ISP and the customer is a link where only provider and customer routers reside, and in my opinion, it is not appropriate for routers to depend on autoconfiguration.
Best regards,
Peter
