f5 and bgp

Ok Thanks for your answer, I'm not really sure how I would add this NULL route in a way that it would get removed when the DNS servers are not answering queries. I understand of course that I can add a static route to the f5 but unless I am mis-understanding something somewhere if I do this and then the DNS servers are both unavailable the /32 will get withdrawn but the /24 will remain which means I will still pull in traffic for my DNS servers which are not available to answer the queries.