diff --git a/lib/cwmp.ts b/lib/cwmp.ts
index 1bece60..9b0fc8e 100644
--- a/lib/cwmp.ts
+++ b/lib/cwmp.ts
@@ -45,6 +45,7 @@ import {
   InformRequest,
   Preset,
   GetRPCMethodsResponse,
+  CpeFault,
 } from "./types";
 import { IncomingMessage, ServerResponse } from "http";
 import { Readable } from "stream";
@@ -1256,6 +1257,41 @@ async function processRequest(
       session.clearProvisions(sessionContext);
     }
     return nextRpc(sessionContext);
+  } else if (rpc.unknownMethod) {
+    if (sessionContext.state === 1) {
+      logger.accessWarn({
+        sessionContext: sessionContext,
+        message: "Method not supported",
+        method: rpc.unknownMethod,
+      });
+
+      const f: CpeFault = {
+        faultCode: "Server",
+        faultString: "CWMP fault",
+        detail: {
+          faultCode: "8000",
+          faultString: "Method not supported",
+        },
+      };
+
+      const res = soap.response({
+        id: rpc.id,
+        acsFault: f,
+        cwmpVersion: sessionContext.cwmpVersion,
+      });
+
+      return writeResponse(sessionContext, res);
+    } else if (sessionContext.state === 2) {
+      const fault = {
+        code: "invalid_response",
+        message: "Response name does not match request name",
+      };
+      recordFault(sessionContext, fault);
+      session.clearProvisions(sessionContext);
+      return nextRpc(sessionContext);
+    } else {
+      return reportBadState(sessionContext);
+    }
   } else {
     // CPE sent empty response
     if (sessionContext.state !== 1) return reportBadState(sessionContext);
diff --git a/lib/soap.ts b/lib/soap.ts
index 9a8cbbd..7894dc1 100644
--- a/lib/soap.ts
+++ b/lib/soap.ts
@@ -730,6 +730,18 @@ function RequestDownloadResponse(): string {
   return "<cwmp:RequestDownloadResponse></cwmp:RequestDownloadResponse>";
 }
 
+function AcsFault(f: CpeFault): string {
+  return `<soap-env:Body:Fault><faultcode>${encodeEntities(
+    f.faultCode
+  )}</faultcode><faultstring>${encodeEntities(
+    f.faultString
+  )}</faultstring><detail><cwmp:Fault><FaultCode>${encodeEntities(
+    f.detail.faultCode
+  )}</FaultCode><FaultString>${encodeEntities(
+    f.detail.faultString
+  )}</FaultString></cwmp:Fault></detail></soap-env:Body:Fault>`;
+}
+
 function faultStruct(xml: Element): FaultStruct {
   let faultCode: string,
     faultString: string,
@@ -838,6 +850,7 @@ export function request(
     cpeRequest: null,
     cpeFault: null,
     cpeResponse: null,
+    unknownMethod: null,
   };
 
   if (!body.length) return rpc;
@@ -959,7 +972,8 @@ export function request(
       rpc.cpeFault = fault(methodElement);
       break;
     default:
-      throw new Error(`8000 Method not supported ${methodElement.localName}`);
+      rpc.unknownMethod = methodElement.localName;
+      break;
   }
 
   return rpc;
@@ -987,6 +1001,7 @@ export function response(rpc: {
   id: string;
   acsRequest?: AcsRequest;
   acsResponse?: AcsResponse;
+  acsFault?: CpeFault;
   cwmpVersion?: string;
 }): { code: number; headers: Record<string, string>; data: string } {
   const headers = {
@@ -1055,6 +1070,8 @@ export function response(rpc: {
           `Unknown method request ${(rpc.acsRequest as AcsRequest).name}`
         );
     }
+  } else if (rpc.acsFault) {
+    body = AcsFault(rpc.acsFault);
   }
 
   headers["Content-Type"] = 'text/xml; charset="utf-8"';
diff --git a/lib/types.ts b/lib/types.ts
index 1f41836..90b2c84 100644
--- a/lib/types.ts
+++ b/lib/types.ts
@@ -526,6 +526,7 @@ export interface SoapMessage {
   cpeRequest?: CpeRequest;
   cpeFault?: CpeFault;
   cpeResponse?: CpeResponse;
+  unknownMethod?: string;
 }
 
 export interface ScriptResult {