Powerline adapters and IPv6

My home network includes a number of devices connected via Powerline (HomePlug) adapters. Back in 2015 I blogged about ‘crosstalk’ between my and my neighbour’s home networks, both of which use Powerline adapters (see my post ‘Waiting for 192.168.1.254…’ (Why I could not access a home hub’s management page)), which I was able to resolve by changing the encryption key so that it is different to the default key used by my neighbour. Since then the Powerline adapters have worked well. However, an unrelated network problem recently highlighted another problem with my Powerline adapters…

In November last year there was an external fault with the broadband service to my house, so I had to contact my ISP (the company BT) to fix the problem. BT does not use highly-skilled field personnel to diagnose broadband problems; they tend to use a ‘shotgun’ approach to problem solving. Their first attempt was to replace my router, a BT Home Hub 5, which I knew was actually working perfectly. I was not going to argue, though, because they replaced the router with the newest model, a BT Smart Hub 2. Unlike the Home Hub 5, the Smart Hub 2 fully supports IPv6. BT’s broadband network has supported IPv6 for several years (see ISPreview – UPDATE All BT Broadband Lines Now Support IPv6 Internet Addresses) so I was expecting the computers on my home network to be assigned IPv6 addresses, but ‘ifconfig‘ and ‘ip address‘ showed they were not being assigned IPv6 addresses when connected via the Powerline adapters, only when connected to the Smart Hub 2 via Wi-Fi.

All my computers have IPv6 enabled:

$ sudo sysctl -a | grep disable_ipv6
[sudo] password for fitzcarraldo: 
sysctl: net.ipv6.conf.all.disable_ipv6 = 0
reading key "net.ipv6.conf.all.stable_secret"
sysctl: reading key "net.ipv6.conf.default.stable_secret"
net.ipv6.conf.default.disable_ipv6 = 0
sysctl: reading key "net.ipv6.conf.eno1.stable_secret"
net.ipv6.conf.eno1.disable_ipv6 = 0
sysctl: reading key "net.ipv6.conf.lo.stable_secret"
net.ipv6.conf.lo.disable_ipv6 = 0
sysctl: net.ipv6.conf.wlp2s0.disable_ipv6 = 0
reading key "net.ipv6.conf.wlp2s0.stable_secret"

$ test -f /proc/net/if_inet6 && echo "IPv6 supported" || echo "IPv6 not supported"
IPv6 supported

The fact that the computers on the home network were allocated an IPv6 address when connected to the Smart Hub 2 via Wi-Fi, and that WhatIsMyIPAddress.com confirmed the BT broadband public network was also allocating an IPv6 address, made me suspect the problem of no IPv6 via the wired network was due to the Powerline adapters.

As more machines were added to my home network over the years, I had to buy more Powerline adapters. In 2014 I bought some NETGEAR XAVB5221 (500 Mbps) Powerline adapters to supplement the superseded model NETGEAR XAVB1301 (200 Mbps) Powerline adapters I bought in 2012. Powerline adapters conforming to the HomePlug AV standard work together, so these had no problem communicating. A schematic diagram of my home network is shown below. To keep things simple, only some of the devices are shown. As you can in the diagram, a NETGEAR XAVB1301 adapter was used to connect the BT Smart Hub 2 to the network; some of the computers were connected via NETGEAR XAVB5221 adapters, and others via NETGEAR XAVB1301 adapters.

I could find no mention of IPv6 for its Powerline adapters in NETGEAR’s documentation and on the NETGEAR Web site. The NETGEAR user manual for the XAV1301 is dated ‘September 2011’ and it lists, under SPECIFICATIONS, compliance with IEEE 802.3 and IEEE 802.3u. The data sheet (no user manual available) for the XAVB5221 is dated ‘2014’ and it lists, under SPECIFICATIONS, compliance with IEEE 1901 and IEEE 802.3.

The Wikipedia page for IEEE 1901-2010 mentions IPv6, so support for IPv6 is relevant to the protocol:

“An IETF RFC Draft address the higher layers of the protocol, namely the specifics of passing IPv6 packets over the PHY and MAC layers of PLC [power-line communication] systems like IEEE 1901.”

I think the following draft Internet Engineering Task Force (IETF) document must be the latest version of the IETF Draft mentioned on the above-mentioned Wikipedia page for IEEE 1901:

Transmission of IPv6 Packets over PLC Networks

Anyway, all this lead me to wonder if the NETGEAR XAVB1301 does not fully comply with IEEE 1901 and does not support IPv6. So I decided to try connecting the BT Smart Hub 2 to the network via a NETGEAR XAVB5221 adapter instead of the older model XAVB1301, as shown in the schematic diagram below.

What I then found was that any computer connected to the network via a NETGEAR XAVB5221 adapter was assigned an IPv6 address in addition to an IPv4 address, and WhatIsMyIPAddress.com showed public IPv6 and IPv4 addresses in a Web browser on the device. However, any computer connected to the network via a NETGEAR XAVB1301 adapter was assigned an IPv6 address in addition to an IPv4 address but WhatIsMyIPAddress.com displayed ‘IPv6 not detected’ in a Web browser. So it transpired that NETGEAR XAVB5221 adapters can handle IPv6 but the older XAVB1301 model cannot.

Although not essential, I toyed with the idea of replacing the older NETGEAR XAVB1301 adapters with XAVB5221 adapters, but that model is no longer on sale. The latest available Powerline adapter model from NETGEAR for wired networking is the PL1000 (1000 Mbps). However, its documentation does not mention IPv6 or IEEE 1901, and the following question on the Amazon UK Web site about IPv6 support for the PL1000, and NETGEAR’s answer on 5 May 2020 makes it clear that the PL1000 does not support IPv6:

Question: Does this model support ipv6? netgear xav1301 adapters only support ipv4. my router & pcs support ipv6 but can’t use ipv6 with my xav1301 adapters.

Answer: Thank you for your interest in the NETGEAR PL1000.

The PL1000 supports IPv4.

If you have any questions, you can also check out our NETGEAR Community at any time.

Best regards,
NETGEAR Amazon UK

Unlike NETGEAR, the TP-Link Web site makes it clear that all TP-Link Powerline adapters currently on sale support IPv6:

Most frequently asked questions about TP-Link powerline devices – Part3: Other questions about Powerline Device

Q3.12: Can TP-Link Powerline devices transfer IPv6 packets?

A: Yes, all the on sale TP-Link powerline devices can transfer IPv6 packets. Kindly note this is supported by default and does not require any configuration, our powerline products do not have setting entries for IPv6 either.

I also asked someone I know who uses TP-Link Powerline adapters and a BT Smart Hub 2, and he confirmed that the TP-Link adapters can handle IPv6.

Therefore, the bottom line is: if you want to use Powerline adapters and IPv6, avoid buying NETGEAR Powerline adapters and look at other manufacturers’ adapters instead. I have only investigated TP-Link’s adapters, which do support IPv6. A number of other companies also manufacture Powerline adapters, but you would need to check if they support IPv6; if necessary contact the manufacturer to be sure.