# Which of the following is NOT a valid mTLS mode in Istio's PeerAuthentication?

Istio, Medium (Advanced), Security. https://k8wiz.com/uquiz/which-of-the-following-is-not-a-valid-mtls-mode-in-istios-peerauthentication

- A. STRICT
- B. PERMISSIVE
- C. DISABLE
- D. OPTIONAL

**Answer:** OPTIONAL

**Explanation:** OPTIONAL is not a valid mTLS mode in Istio's PeerAuthentication. The valid modes are STRICT (require mTLS), PERMISSIVE (allow both mTLS and plain text), and DISABLE (no mTLS).