What is a Taboo Contract?

 In Cisco ACI (Application Centric Infrastructure), a taboo contract is a special type of contract used to explicitly deny specific types of traffic between endpoint groups (EPGs), even if other contracts would otherwise allow it.

🔍 What is a Taboo Contract?

• Purpose: Taboo contracts are designed to block traffic that matches certain filters. They override any other contracts that might permit that traffic.
• Application: Unlike standard contracts which are applied between EPGs (one consuming and one providing), taboo contracts are applied to an entire EPG. This means they affect all traffic originating from or destined to that EPG 

• Use Case: For example, if you want to ensure that an EPG never uses insecure protocols like HTTP (port 80) or Telnet (port 23), you can apply a taboo contract with filters for those ports 

🛑 Key Characteristics

• Deny Action: Taboo contracts only support the "deny" action. They are used to block traffic, not to permit it.
• Logging: Optionally, taboo contracts can also log the denied traffic for auditing or troubleshooting purposes 
• Priority: They take precedence over regular contracts. If a packet matches a taboo filter, it is dropped—even if a regular contract would otherwise allow it 

⚠️ Best Practices & Cautions

• Many experts recommend avoiding taboo contracts unless absolutely necessary. Instead, it's often better to design your standard contracts carefully to only permit the desired traffic 
• Taboo contracts can add complexity and may lead to unintended traffic drops if not managed properly