The 30-Second Version
Client SSL Profile: Handles traffic FROM clients (browsers) TO F5. Your server certificate lives here.
Server SSL Profile: Handles traffic FROM F5 TO your backend servers. Only needed for re-encryption.
The confusion: "Client" and "Server" refer to who F5 is talking to, not which certificate type.
The Simple Answer
Client SSL Profile
- Handles where users connect TO the F5
- F5 acts as a server in this connection
- Your public certificate goes here
- Always needed for HTTPS virtual servers
Server SSL Profile
- Handles where F5 connects TO your backend
- F5 acts as a client in this connection
- Usually doesn't need a certificate
- Only needed if backend requires HTTPS
Visual Explanation
┌────────────────────────────────────────────────────────────────────────────┐ │ │ │ ┌──────────┐ ┌─────────────┐ ┌──────────┐ │ │ │ │ HTTPS │ │ HTTP or │ │ │ │ │ Client │ ───────────▶ │ F5 LTM │ ──────────▶ │ Server │ │ │ │ (Browser)│ │ │ HTTPS │ (Backend)│ │ │ │ │ ◀─────────── │ │ ◀────────── │ │ │ │ └──────────┘ └─────────────┘ └──────────┘ │ │ │ │ │ │ │ │ │ │ ┌──────┴──────┐ │ │ │ │ ┌─────┴─────┐ ┌─────┴─────┐ │ │ │ │ │ Client SSL│ │Server SSL │ │ │ │ │ │ Profile │ │ Profile │ │ │ │ │ └───────────┘ └───────────┘ │ │ │ │ │ │ │ │ │ ▼ ▼ ▼ ▼ │ │ │ │ "CLIENT" YOUR CERT (optional) "SERVER" │ │ connection GOES HERE backend connection │ │ encryption │ │ │ └────────────────────────────────────────────────────────────────────────────┘
The naming is from F5's perspective:
- • Client SSL = manages the CLIENT's connection (F5 is the server)
- • Server SSL = manages the SERVER's connection (F5 is the client)
Why The Naming Is Counterintuitive
When you first hear "Client SSL profile," you might think:
Actually:
| Profile | Who F5 is talking to | F5's role | Certificate needed |
|---|---|---|---|
| Client SSL | Clients (browsers) | Server | Your server cert |
| Server SSL | Backend servers | Client | Usually none |
What Goes Where
Certificate Placement Guide
| What You Want | Which Profile | Which Setting |
|---|---|---|
| Present certificate to users | Client SSL | Certificate Key Chain |
| Present intermediate chain to users | Client SSL | Chain (in Cert Key Chain) |
| Require users to have certificates (mTLS) | Client SSL | Client Authentication |
| Trust specific CAs for user certs | Client SSL | Trusted Certificate Authorities |
| Present certificate to backend (rare) | Server SSL | Certificate Key Chain |
| Verify backend certificate | Server SSL | Server Authentication |
| Trust specific CAs for backend certs | Server SSL | Trusted Certificate Authorities |
Real-World Scenarios
Scenario A: Standard HTTPS Website (SSL Offload)
What you need:
- Client SSL Profile (with your certificate)
- Server SSL Profile (not needed)
Why: F5 terminates SSL. Backend gets plain HTTP. Simple and common.
Scenario B: End-to-End Encryption
What you need:
- Client SSL Profile (with your public certificate)
- Server SSL Profile (to encrypt to backend)
Why: Compliance requires encryption at rest. F5 decrypts, inspects, re-encrypts.
Scenario C: Mutual TLS (mTLS) with Clients
What you need:
- Client SSL Profile (with your cert + Client Authentication)
- Server SSL Profile (not needed if backend is HTTP)
Client SSL Config: Certificate Key Chain: Your server cert | Client Authentication: Require | Trusted CAs: CA that issued client certs
Scenario D: Backend Requires Client Certificate
What you need:
- Client SSL Profile (with your public certificate)
- Server SSL Profile (with certificate to present to backend)
This is rare but happens with backend APIs that require mTLS, zero-trust architectures, or service mesh integrations.
Configuration Comparison
Client SSL Profile Settings
| Setting | Purpose | Typical Value |
|---|---|---|
| Certificate | Your server cert | www.example.com.crt |
| Key | Private key | www.example.com.key |
| Chain | Intermediate CA(s) | DigiCertCA.crt |
| Ciphers | Allowed ciphers | ECDHE+AES-GCM:ECDHE+AES |
| Options | TLS versions | No TLSv1, No TLSv1.1 |
| Client Authentication | Require client certs? | Ignore (usually) |
Server SSL Profile Settings
| Setting | Purpose | Typical Value |
|---|---|---|
| Certificate | Cert for backend (rare) | Often empty |
| Server Name | SNI to send to backend | Backend hostname |
| Server Authentication | Verify backend cert? | Ignore (trust by network) |
| Ciphers | Allowed algorithms | Match backend requirements |
| Options | TLS versions | Match backend requirements |
Common Mistakes
Mistake 1: Putting Your Certificate in Server SSL
Wrong thinking: "Users are connecting to my server, so I need Server SSL"
Reality: Users connect TO F5 as a client. F5 is the server. Certificate goes in Client SSL.
Mistake 2: Creating Server SSL When Not Needed
Wrong thinking: "I have HTTPS, so I need both profiles"
Reality: You only need Server SSL if your backend requires HTTPS. Most setups don't.
Mistake 3: Confusing Client Auth Settings
Wrong thinking: "Client Authentication in Server SSL is for authenticating clients"
- • Client SSL → Client Authentication = Require users to present certs
- • Server SSL → Server Authentication = Verify backend server's cert
Mistake 4: Wrong Chain Location
Wrong thinking: "Trusted Certificate Authorities is where my chain goes"
- • Chain (in Certificate Key Chain) = Intermediates to SEND to clients
- • Trusted CAs = CAs to TRUST for validating client certificates
Quick Decision Guide
┌─────────────────────────────────────────────────────────────┐ │ DO YOU NEED HTTPS? │ │ │ │ │ YES │ │ │ │ │ ▼ │ │ ┌─────────────────────────────────┐ │ │ │ CREATE CLIENT SSL PROFILE │ │ │ │ Add your certificate here │ │ │ └─────────────────────────────────┘ │ │ │ │ │ ▼ │ │ Does your BACKEND need HTTPS? │ │ │ │ │ │ YES NO │ │ │ │ │ │ ▼ ▼ │ │ ┌──────────────┐ ┌──────────────┐ │ │ │Also create │ │ You're done! │ │ │ │Server SSL │ │ (SSL Offload)│ │ │ │Profile │ └──────────────┘ │ │ └──────────────┘ │ │ │ └─────────────────────────────────────────────────────────────┘
Verification Commands
# Check which profiles are assigned to a virtual server
tmsh list ltm virtual my-virtual-server profiles
# Example output:
# profiles {
# my-client-ssl {
# context clientside ← This is Client SSL
# }
# my-server-ssl {
# context serverside ← This is Server SSL
# }
# tcp { }
# }
# Test the client-facing certificate
openssl s_client -connect your-vip:443 -servername your-domain.com
# Test what the backend sees (from F5 shell)
curl -vk https://backend-server:443Frequently Asked Questions
Related Resources
F5 SSL Profiles Explained
The foundational guide to understanding what SSL profiles are and why they exist.
F5 Certificate Installation
Step-by-step guide to installing SSL certificates on BIG-IP.
mTLS (Mutual TLS) Guide
Deep dive into mutual TLS and client certificate authentication.
F5 Certificate Chain Configuration
Configure intermediate certificate chains correctly on BIG-IP.
How TLS Works
Complete guide to TLS handshakes and certificate verification.
Cipher Suite Decoder
Understand cipher suites and their components for SSL profile configuration.