ginuerzh/gost · error

SOCKS5 mbind on failure

Error message

SOCKS5 mbind on %s failure

What it means

During mux-bind session setup, initSession sends a SOCKS5 BIND request on the multiplexed session; the server's reply code was not gosocks5.Succeeded, so Handshake aborts with this error. It means the proxy rejected the multiplexed bind for the requested address.

Solutions

1. Check the proxy server supports mux-bind and is configured with the same bind address; fix the transporter's bindAddr.
2. Inspect proxy ACLs and allow the bind address/port.
3. Retry or reduce concurrent sessions; inspect server logs for the reply code.
4. Fall back to plain SOCKS5 connector/transporter if the server lacks mux-bind support.

Example fix

// before
SOCKS5MuxBindTransporter("192.168.1.1:6000") // address rejected by proxy
// after
SOCKS5MuxBindTransporter("") // let server choose an allowed bind address, or use an ACL-approved addr

// Verify proxy reachability before Handshake
conn, err := net.DialTimeout("tcp", proxyAddr, 5*time.Second)
if err != nil { return err }
conn.Close()

session, err := transporter.Handshake(ctx, conn)
if err != nil {
	if strings.Contains(err.Error(), "mbind on") {
		// server refused mux bind: backoff then retry, or fall back to plain connector
		time.Sleep(backoff)
		return transporter.Handshake(ctx, dialAgain())
	}
	return err
}

When it happens

Trigger: SOCKS5MuxBindTransporter establishing a new mux session (initSession, called from Handshake): the SOCKS5 reply to the mbind request carries a failure code (proxy denies bind, address not permitted, server overloaded).

Common situations: Proxy does not support the mux-bind extension; server-side bind host/port misconfigured (bindAddr unreachable or forbidden); proxy ACL rejects the configured bind address; too many concurrent binds.

Related errors

• SOCKS5 bind on failure
• SOCKS5 udp relay failure
• bad request
• Bind on failure
• bind: peer connect failure

AI-assisted analysis of ginuerzh/gost@a33fdbf4c9 (2026-09-02). Data as JSON: /api/errors/d603d224bfe19d60. Report an issue: GitHub.

Appendix: source

Thrown at socks.go:520

		return nil, err
	}

	if Debug {
		log.Log("[socks5] mbind\n", req)
	}

	reply, err := gosocks5.ReadReply(conn)
	if err != nil {
		return nil, err
	}

	if Debug {
		log.Log("[socks5] mbind\n", reply)
	}

	if reply.Rep != gosocks5.Succeeded {
		log.Logf("[socks5] mbind on %s failure", addr)
		return nil, fmt.Errorf("SOCKS5 mbind on %s failure", addr)
	}
	baddr, err := net.ResolveTCPAddr("tcp", reply.Addr.String())
	if err != nil {
		return nil, err
	}
	log.Logf("[socks5] mbind on %s OK", baddr)

	// Upgrade connection to multiplex stream.
	session, err := smux.Server(conn, smux.DefaultConfig())
	if err != nil {
		return nil, err
	}
	return &muxSession{conn: conn, session: session}, nil
}

func (tr *socks5MuxBindTransporter) Multiplex() bool {
	return true
}

View on GitHub (pinned to a33fdbf4c9)