WiFiClient cannot connect to IPv6 link local address

[Jamesits]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: ESP8266MOD
• Core Version: 2.5.2
• Development Env: Arduino IDE
• Operating System: Windows

Settings in IDE

• Module: Wemos D1 R2 & mini
• Flash Size: 4MB
• lwip Variant: v2 IPv6 Higher Bandwidth
• Reset Method: ck
• CPU Frequency: 80Mhz
• Upload Using: SERIAL
• Upload Speed: 921600

Problem Description

As per #5136, IPv6 is supported on the recent versions of ESP8266. However, I observed that WiFiClient.connect() is not able to connect to an IPv6 link-local IP address (fe80::/10) on the same network with the ESP8266.

MCVE Sketch

#include <ESP8266WiFi.h>

#define STA_SSID "your-ssid"
#define STA_PSWD "your-wifi-password"
#define SERVER_IP "fe80::aaaa:bbff:fecc:dddd"

IPAddress server;
WiFiClient client;

void setup() {
  Serial.begin(115200);

  WiFi.mode(WIFI_STA);
  WiFi.setAutoConnect(true);
  WiFi.setAutoReconnect(true);
  WiFi.begin(STA_SSID, STA_PSWD);
}

void loop() {
    Serial.println("\nStarting connection...");
    // if you get a connection, report back via serial:
    server.fromString(SERVER_IP);
    if (client.connect(server, 8000)) {
      Serial.println("connected");
      // Make a HTTP request:
      client.println("GET / HTTP/1.0");
      client.println();
    } else {
      Serial.println("Failed to connect");
    }
    delay(500);
}

Debug Messages

Sketch output:

Starting connection...
Failed to connect

I've done a packet capture on the server and can see NO packets from ESP8266.

[theGeekyLad]

Is there any update on this?

[d-a-v]

I am still not an IPv6 specialist.

My linux laptop cannot reach my server through fe80: and I need to add the interface name,
like: $ ping fe80:...:852c%wlp2s0.
However $ ping fd6f:...:852c works.

Can you give it a try ?

[Jamesits]

@d-a-v Normally you'd need to bind to an interface when using fe80 link-local IPs since they are bound to an interface. There is no way to do this on the ESP8266 SDK...

[d-a-v]

lwIP has it and we use it:

Arduino/libraries/ESP8266WiFi/src/include/UdpContext.h

Lines 99 to 104 in a05a71f

	#if LWIP_IPV6
	// Set zone so that link local addresses use the default interface
	if (IP_IS_V6(&_pcb->remote_ip) && ip6_addr_lacks_zone(ip_2_ip6(&_pcb->remote_ip), IP6_UNKNOWN)) {
	ip6_addr_assign_zone(ip_2_ip6(&_pcb->remote_ip), IP6_UNKNOWN, netif_default);
	}
	#endif

Arduino/libraries/ESP8266WiFi/src/include/ClientContext.h

Lines 134 to 139 in c312a2e

	#if LWIP_IPV6
	// Set zone so that link local addresses use the default interface
	if (IP_IS_V6(addr) && ip6_addr_lacks_zone(ip_2_ip6(addr), IP6_UNKNOWN)) {
	ip6_addr_assign_zone(ip_2_ip6(addr), IP6_UNKNOWN, netif_default);
	}
	#endif

netif_default should be set to the STA interface (<= this is next version and this is current version).

[d-a-v]

I was asking to try because fd6f: is not public and is a reserved address dedicated to local area, as fe80: is reserved for the link only. I don't remember and I have no ipv6 environment right now to check if the ipv6 implementation of lwIP binds to this domain too.
Please correct me if I'm mistaken.