...and the ISP that insists that it be used. It was quite the unpleasant surprise the first time I discovered that you can't turn off DHCP, which means forget using DNS and a Windoze domain on that subnet.
My usual solution for small clients that are stuck with this ISP (for whatever reason) is to create a proper network behind a separate router of my choosing. The Westell network can be "public" and the inner network is secured. It's a pain to set up routing through the Westell, but at least it works and you are reasonably isolated from that ISP's forced insanity.
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