Why is my 2021 Apple TV 4K sending ICMPv6 router advertisements?

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Level 1

10 points

Why is my 2021 Apple TV 4K sending ICMPv6 router advertisements?

I'm having the same symptoms found in the following HomePod mini thread after adding a 2021 Apple TV 4K to my network:

https://discussions.apple.com/thread/252367920

I have two original (2017) Apple TV 4Ks on my network and just added a 2021 Apple TV 4K. About the same time I connected the 2021, I started getting IPv6 ULAs (with an fdb4: prefix) followed by "No Internet" messages on both wired and wireless clients, both Mac and Windows. This IPv6 address assignment would coincide with those devices dropping their DHCP-assigned IPv4 addresses and usually eventually assigning themselves 169.254.x.x IPv4 addresses. I ran a WireShark packet capture on my iMac ethernet interface as I plugged it in (with iMac Wi-Fi off), and I found the culprit was the 2021 Apple TV 4K.

It was initially difficult to diagnose as my 2021 Apple TV is connected wirelessly only, so I wouldn't see the issue when I took down the APs. No other device is doing this, including the two 2017 Apple TVs. My router doesn't issue RAs; I do not have IPv6 set up on the router for the WAN (even though my ISP supports it) or LAN.

I'm going to try to put a support ticket in, but I have no idea how long it's going to take to find a support representative who understands the problem, let alone is knowledgeable enough on IPv6 to submit a meaningful ticket to engineering. It's breaking connectivity with many of my devices.

I decided not to do any rules to block those messages in case doing so would break HomeKit or something else. I've got the 2021 unplugged for now until I find out more about what's going on.

I see no good reason why Apple TVs should send router advertisement messages! :-D (H/T: R. Hamilton)

Posted on Jun 7, 2021 6:07 AM

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Answer 1

Best reply

EddyGeez

Level 1

21 points

Jun 16, 2021 9:00 AM in response to Dirac

These IPv6 RAs are a problem for anybody who uses "strict" VPN software, like Cisco AnyConnect, on an IPv6-enabled network.

The RAs are short-lived (1800s), so when they expire, events like this get logged by AnyConnect:

#
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] A network interface address has gone down.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] A routing table change notification has been received.  Starting automatic correction of the routing table.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] A new network interface address has been detected.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] Reconfigure reason code 15: New network interface.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] A routing table change notification has been received.  Starting automatic correction of the routing table.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] Automatic correction of the routing table has been successful.
vpnagentd: (libvpncommon.dylib) [com.cisco.anyconnect.vpn:acvpnagent] The entire VPN connection is being reconfigured.

Cisco AnyConnect then proceeds to run /sbin/pfctl -F states 2>&1 (amongst other pfctl commands to configure its firewall rules) which flushes all the NAT and filter table state. This, of course, causes all existing connections (such as ssh sessions) to be dropped.

It's super annoying. So anybody working from home on a network with a 2021 Apple TV 4K or a HomePod Mini and needs AnyConnect for remote access has issues approximately every 30 minutes, based on these Thread RAs.

I don't believe Apple is doing anything wrong here, but they should offer a way to disable the Thread IPv6 RAs for those of us who don't need them, especially since their presence has undesirable side-effects.

For reference, this is a sample of the RAs that I see:

interface
{
	AdvSendAdvert on;
	AdvManagedFlag off;
	AdvOtherConfigFlag off;
	AdvReachableTime 0;
	AdvRetransTimer 0;
	AdvCurHopLimit 0;
	AdvDefaultLifetime 0;
	AdvHomeAgentFlag off;
	AdvDefaultPreference medium;
	AdvSourceLLAddress on;

    prefix fda5:29ff:3b2c:1::/64
	{
		AdvValidLifetime 857;
		AdvPreferredLifetime 0;
		AdvOnLink on;
		AdvAutonomous on;
		AdvRouterAddr off;
	}; # End of prefix definition

    route fdb0:dd88:d3ec::/64
	{
		AdvRoutePreference medium;
		AdvRouteLifetime 1800;
	}; # End of route definition
}; # End of interface definition

I don't know how to escalate this issue within Apple to have them add a setting to disable the Thread RAs, but maybe somebody reading this knows...

P.S. these IPv6 RAs negatively affect AnyConnect on both Mac and Windows machines!

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Answer 2

chris_g1

Community Specialist

Jun 8, 2021 8:13 AM in response to Dirac

Hello Dirac,

Thank you for using Apple Support Communities! It sounds like you’re having a problem with your Apple TV 2021 after connecting it to your network. We would be happy to help!

Let's start by restarting devices and making sure the software is up to date. Following that, we recommend trying a different network to test the issue further. If we can successfully isolate the issue specifically to the Wi-Fi network, you may want to contact your internet service provider.

Cheers!

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