Testing a BGP tunnel with Hurricane Electric on a RB1100AH (6to4 interface), receiving approx 6500 routes, running v4.17.

CPU is 100% even after accepting all the routes. As soon as I take the peer down, CPU goes back to 0.

This doesn't happen if you discard all routes and set a manual default.

Any suggestions?

Paste your config in bgp and filter.