# Client SSL vs Server SSL Profiles on BIG-IP

> A BIG-IP can sit in the middle of a TLS connection and decrypt it. A client-ssl profile makes the BIG-IP the TLS server to the client; a server-ssl profile makes it the TLS client to the pool. Knowing which side each profile owns is the key to offload, bridging, and re-encryption designs.

Source: https://ronutz.com/en/learn/f5-clientssl-vs-serverssl  
Updated: 2026-06-29  
Related tools: https://ronutz.com/en/tools/f5-ssl-profile-explainer

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A BIG-IP virtual server can do something a plain router cannot: terminate a TLS connection, look inside the cleartext, and open a fresh TLS connection to the backend. Two different profile types govern the two halves of that picture, and they play opposite roles.

## Client SSL: the BIG-IP is the server

A `client-ssl` profile faces the **client**. With it attached, the BIG-IP acts as the TLS *server*: it presents a certificate, completes the handshake the browser started, and decrypts the client's traffic. This is the profile that holds your public-facing certificate and private key. Everything the client sees about your site's TLS — the certificate, the negotiated version, the cipher — comes from here.

## Server SSL: the BIG-IP is the client

A `server-ssl` profile faces the **pool member**. With it attached, the BIG-IP acts as the TLS *client* toward the backend: it opens a new TLS connection to the server and, if configured, validates the server's certificate against a trusted CA (certificate authority). The backend sees the BIG-IP as just another TLS client.

## Three common shapes

These two profiles combine into the patterns you will actually deploy:

- **SSL offload** — a `client-ssl` profile only. The BIG-IP terminates client TLS and talks **cleartext** to the pool. Simplest and fastest, but the server leg is unencrypted, so it is only safe on a trusted internal segment.
- **SSL bridging (re-encryption)** — **both** a `client-ssl` and a `server-ssl` profile. The BIG-IP decrypts from the client, can inspect or modify the traffic, then re-encrypts to the pool. This is what you need when policy or compliance requires encryption end to end while still allowing layer 7 processing.
- **SSL pass-through** — **neither** profile. The BIG-IP forwards the encrypted bytes untouched. No certificate, no inspection, no layer 7 features.

## Why the distinction matters

A surprising number of TLS tickets come down to attaching the wrong profile to the wrong side, or expecting the backend to be validated when only a `client-ssl` profile is present. Validation of the *backend* server certificate is a `server-ssl` concern (`peer-cert-mode` plus `ca-file`); validation of a *client* certificate is a `client-ssl` concern. When you read a profile, the first question to settle is always: which side does this one own?

Paste either profile into the SSL profile explainer and it will tell you its role, the protocol versions it permits, and what each setting does.