Does ULA useless for home LAN network?

Hi forum!

My home network on the OpenWrt router has only one LAN.
Each device in my network gets:

  1. ipv4 address from DHCPv4 range, e.g. 192.168.1.102
  2. ipv6 Link-local address automatically generated, e.g. fe80::3cab:1ef3:2158:3ad2
  3. ipv6 GUA address from DHCPv6-PD prefix, e.g. 2001:db80:abcd:1234::567
  4. ipv6 ULA address, e.g. fd27:f9b7:256f:0:82d3:1ef3:f58:e4c25

Everything works fine, but I'm wondering for what purposes the OpenWrt configuration has ULA enabled by default, and if ULA is useless for my network, then maybe I should completely disable ULA with assumption that link-local (fe80::/10) will be enough for internal communication within the LAN?

Research I made:

  • If I ping any device in my network (e.g. ping mypc1), it will ping using link-local address only.
  • From comment: "As per RFC6724, ULA is less preferred than all IPv4 (represented by ::ffff:0:0/96 in the preferences table of every OS). So, if you have IPv4 enabled on a host, it will use IPv4 before any attempt to use ULA (you can try it in your network. Give a host an A and an AAAA record, the latter with a ULA. Then try to connect to it. If IPv4 works, the ULA will never be used."

So, does the ULA really useless?
If not, what is the practical application of ULA for a small network if user does not need to do ipv6 traffic routing between sub-networks?

In your specific use case, if you are never doing IPv6 bridging with another network (via VPN network joining or the like), you're right, it's useless in your environment.

1 Like

ULA is roughly an IPv6 equivalent to rfc1918 (e.g. 192.168.0.0/16 and friends) addresses, it goes beyond link-local addresses (for which you'd have to specify the outgoing interface). If you assume that your internet will never go down (which is wishful thinking to some extent) nor changes prefixes, GUAs might do just as well, but beyond that, ULA addresses keep your LAN working, independent of your WAN connectivity.

While it's possible to disable ULAs and which might be useful in very specific circumstances, I wouldn't recommend doing so - they serve a valid purpose.

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Does this statement applicable to IPv6-only networks?
Because as I understand it (please correct me if i'm wrong), if I have enabled both IPv4 and IPv6 in my home network, I can rely on the local IPv4 addresses if for some reason the ipv6 internet (GUA) from my ISP will go down (IPv4 addresses (not ULA) will keep my LAN working, because IPv6 ULA is less preferred than IPv4 as per RFC6724).

So, again, sorry, I'm just asking for the final clarification:

  • IF I have enabled both IPv4 and IPv6 (link-local and GUA) addresses in my home network,
  • AND if I won't do any IPv6 bridging/routing between the networks (e.g. bridging between local LAN, IOT, or Guest networks),
  • AND because ULA is less preferred than all IPv4 addresses as per RFC6724,
  • THEN the ULA can be considered as useless, and the only reason to keep ULA enabled in this home LAN network is <what exactly>?