---
title: tls.client.certificate.is_cert_unknown
summary: null
url: >-
  https://www.fastly.com/documentation/reference/vcl/variables/client-connection/tls-client-certificate-is-cert-unknown
---

**Type:** BOOL  
**Access:** read-only

**Available in:** recv, hash, deliver, log

True if this connection is set to mutual TLS optional mode and the client certificate was received, but some other (unspecified) issue arose in processing the certificate, rendering it unacceptable.