SIP

420 Bad Extension

The server did not understand the protocol extension specified in a Require or Proxy-Require header. The Unsupported header lists the unknown extensions.

On this page

When You See This Code

When the request includes a Require header with SIP extensions that the server does not support.

How to Fix

Check the Unsupported header in the response. Remove the unsupported extension from the Require header or make it optional via Supported.

Specification

View RFC / Specification →

Compare With

100 Trying 180 Ringing 181 Call Is Being Forwarded 182 Queued 183 Session Progress 199 Early Dialog Terminated 200 OK 202 Accepted 204 No Notification 300 Multiple Choices 301 Moved Permanently 302 Moved Temporarily

Guides

401 Unauthorized vs 403 Forbidden: When to Use Each Security & Authentication

SIP Response Codes: Understanding VoIP Call Flow Real-Time Protocols

SIP Call Flow: Understanding Session Setup Real-Time Protocols

WebRTC Signaling with SIP and WebSocket Real-Time Protocols

RFC 3261: SIP Protocol Deep Dive Protocol Deep Dives

TLS 1.3: Faster, Simpler, More Secure Protocol Deep Dives

Glossary

Status Code Request Method (HTTP Verb) TLS Handshake Authentication TCP/IP Port Number NAT (Network Address Translation) Socket Request-Response Model RFC (Request for Comments) Connection-Oriented Full-Duplex SRV Record SIP Dialog Signaling SIP Registrar STUN (Session Traversal Utilities for NAT) TURN (Traversal Using Relays around NAT) SDP (Session Description Protocol) SIP INVITE SIP Proxy Server SIP Redirect Server SIP Transaction SIP User Agent SIP Trunk RTP (Real-time Transport Protocol) SRTP (Secure Real-time Transport Protocol) SIP ACK SIP BYE SIP CANCEL SIP OPTIONS SIP SUBSCRIBE/NOTIFY B2BUA (Back-to-Back User Agent) SBC (Session Border Controller) Codec Negotiation SIP Response Classes VoIP (Voice over IP) Presence (SIP) PBX (Private Branch Exchange) MFA (Multi-Factor Authentication) TLS Versions

Frequently Asked Questions

What is SIP 420 Bad Extension?

The server did not understand the protocol extension specified in a Require or Proxy-Require header. The Unsupported header lists the unknown extensions.

When do you see SIP 420 Bad Extension?

When the request includes a Require header with SIP extensions that the server does not support.

How to fix SIP 420 Bad Extension?

Check the Unsupported header in the response. Remove the unsupported extension from the Require header or make it optional via Supported.