Yes, it is recommended getting CCNA before continuing CCNP track. but ...
if u do not have CCNA and pass all 3 CCNP exams, you will be awarded CCNP cert after passing CCNA (pass CCNA within 3 years).
Note that You must pass all 3 CCNP Pro level exams within 3 years of passing 1st Pro level. in other words, each exam is valid for 3 years only.
other Pro tracks have 4-5 exams.
to check your validity, expiration dates, or progress, go to this site
I failed my ccnp R&S re-certification.
I'm sorry to read that.
Now I have to start from scratch and take 3 exams. But my question is: do I need to take the CCNA R&S again?
If you have renewed your CCNA R&S by passing a CCNA level exam after your last passed CCNP level exam, it may be still valid, but i fear, that that will be not the case. Check in the certification tracking, iif you still have a valif´d CCNA R&S certification, or if the CCNA R&S certification is also expired. If your CCNA R&S certification is also expired, you have akso to start your CCNA R&S from scratch ...