Traffic flow in F5 LTM

Client → Virtual Server (VIP) → Profiles/iRules → Pool Selection → Server → Response back via BIG-IP

Client Sends Request

• User connects to VIP (Virtual IP).

• Packet reaches BIG-IP.

VLAN & Self-IP Check

• BIG-IP checks incoming interface.

• Validates VLAN and routing.

• Performs route lookup.

Virtual Server (VIP) Match

• BIG-IP checks:

  • Destination IP

  • Port

  • Protocol

• If match found → process continues.

• If no match → traffic dropped.

Profile Processing

Profiles define how traffic behaves:

• TCP Profile → connection settings

• SSL Profile → decrypt/encrypt

• HTTP Profile → enables Layer 7 inspection

• Persistence Profile → sticky sessions

If SSL is enabled:

• Traffic is decrypted here (Client SSL profile).

iRules (If Configured)

Custom logic executed:

• Redirect HTTP to HTTPS

• Route based on URI

• Block specific IP

• Modify headers

iRules execute at specific events (CLIENT_ACCEPTED, HTTP_REQUEST, etc.)

Load Balancing Decision

BIG-IP selects a pool member based on:

• Round Robin

• Least Connections

• Ratio

• Fastest

Also checks:

• Server health monitor status

If server is down → skipped.

Server-Side Connection Created

Important concept:

F5 is a Full Proxy

It creates:

• One connection between Client ↔ BIG-IP

• Another connection between BIG-IP ↔ Server

Client never talks directly to the server.

Server Response Returns

Response comes back:

• May be modified by iRules

• Re-encrypted (Server SSL profile if used)

• Sent back to client