[Networkmanager] IPv6 Prefix Length

Robert Nichols rnicholsNOSPAM at comcast.net
Fri Mar 10 21:46:13 UTC 2023

On a host that is acting as a router, how do I get NetworkManager to request an IPv6 address block larger than a single /128 address? By fiddling with various options in the Network Connections GUI, I was just once able to get a /64 prefix. That happened when I set "Method" to "Shared with other computers", which saved "IPV6_AUTOCONF=shared" (a totally undocumented setting) in the interface's ifcfg file. But, that /64 prefix did not survive a reboot, and now I can't get it back at all.

A /64 prefix is bad enough (I'd like to confine some devices to their own subnet), but it's a lot better than a /128, which would force me to use IPv6 NAT, defeating the primary purpose of IPv6. (Comcast/Xfinity now appears to limit residential customers to a /64 -- no subnetting.)

Bob Nichols     "NOSPAM" is really part of my email address.
                 Do NOT delete it.

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