Re: Problem with IPv6 privacy addresses in 7.0

[Tj <tj.iam.tj@proton.me>]

I believe I hit this on a router using Debian 13 with v7.0.* kernel this week that
uses systemd-networkd to configure IPV6 RA and prefix delegation after
moving from v6.19.*.

Symptom was the router could no longer reach public IPv6 addresses
itself but forwarding was unaffected.

The ISP (Starlink) provides a /64 prefix via RA and a /56 via DHCPv6. networkd
allocates a static suffix address from both to the WAN-side interface.

I discovered after much experimentation that instead of the usual /56
address being the source it was choosing the /64 and failing.

Router uses policy routing so my work-around was to add a rule so the
/64 address is added to the WAN interface's route table.

[RoutingPolicyRule]
To=::/0
From=2a0d:3344:aaaa:bbbb::/64
Priority=30100
Table=starlink

The WAN interface config for  RA and PD is:

[IPv6AcceptRA]
UseGateway=yes
UseDNS=no
UseDomains=no
Token=static:::ff
# when RouteTable is set a table name is explicitly required in any [Route] section without a Table= of its own
# names defined in /etc/systemd/networkd.conf.d/51-RouteTable.conf as:  [Network] RouteTable=
RouteTable=starlink

[DHCPv6]
UseAddress=no
UseDNS=no
UseNTP=no
UseHostname=no
UseDomains=no
UseDelegatedPrefix=yes
PrefixDelegationHint=::/56
## asked for in RFE https://github.com/systemd/systemd/issues/31566
##RouteTable=starlink

[DHCPPrefixDelegation]
Announce=false
UplinkInterface=:self
Assign=yes
Token=static:::1
SubnetId=0xff