Specifying link-local address in rc.conf

[Michael Gmelin]

On Mon, 6 Jul 2020 22:58:54 +0200
Niclas Zeising <zeising+freebsd at daemonic.se> wrote:

> On 2020-07-06 13:05, Niclas Zeising wrote:
> > Hi!
> > Is it possible to specify a link-local address in rc.conf, and get
> > only that link-local address?
> > 
> > When I add a specific link-local address, such as fe80::1/64, to an 
> > interface from the command line, and then add a global uincast
> > address, it works as expected, I do not get an additional
> > link-local address. When I try to do the same in rc.conf however,
> > it does not work. I have added the following:
> > ifconfig_vtnet0_inet6="inet6 fe80::1/64"
> > ifconfig_vtnet0_alias0="2001:6b8::1/64"
> > to rc.conf, but when restarting, I get both fe80::1 and a
> > EUI64-based link-local address assigned to the interface.  It does
> > not matter which order I specify the entries in rc.conf.
> > I have tried changing the sysctl net.inet6.ip6.auto_linklocal to 0
> > in /etc/sysctl.conf, but that does not work (it seems it takes
> > effect too late, the interface still has the AUTO_LINKLOCAL flag
> > set according to ifconfig).
> > I tried adding -auto_linklocal to the ifconfig_* lines in
> > /etc/rc.conf, and while this removes the AUTO_LINKLOCAL flag from
> > the interface, a EUI64 based link-local address is still assigned
> > to the interface.
> > 
> > While there might not be much of a problem having mulitple
> > link-local addresses, this is surprising.  Adding a specific
> > link-local address to an interface, even from rc.conf, shouldn't
> > mean that the EUI64-one is created.  Perhaps something like
> > ifconfig_IF_linklocal="" should be added, or this is a bug in
> > rc.network.  I tried looking through rc.network and related rc
> > files, but I didn't find anything obvious, and I couldn't really
> > figure out how addresses are added to interfaces during boot.
> > 
> > This is causing issues when I want for instance rtadvd to use the 
> > fe80::1/64 address as source for router advertisements, since it
> > picks the EUI64 link-local address as source (which means this also
> > ends up in client routing tables as the default gateway).  I can
> > work around this problem by adding fe80::1/64 with prefer_source,
> > but I would prefer if there only was one link-local address on an
> > interface.
> > 
> > All of this is on FreeBSD 12.1.
> > 
> > Perhaps I'm just missing something, but this behavior feels a
> > little surprising.
> > 
> > I can share more detailed configuration, and perhaps the whole
> > virtual machine I'm testing on, if needed.
> > 
> > Regards  
> 
> I did some more digging.  It only happens when there's also an 
> ifconfig_IF for IPv4 in the /etc/rc.conf.
> 
> Not working configuration (/etc/rc.conf)
> ifconfig_vtnet0="192.168.0.1/24"
> ifconfig_vtnet0_ipv6="inet6 fe80::1/64"
> ifconfig_vtnet0_alias0="inet6 2001:6b8::/64"
> 
> This configuration creates an EUI64-based link-local addess on vtnet0
> as well.
> 
> Working configuration (apart from no IPv4)
> ifconfig_vtnet0_ipv6="inet6 fe80::1/64"
> ifconfig_vtnet0_alias0="inet6 2001:6b8::/64""

> 

This works:

ifconfig_vtnet0="inet6 -auto_linklocal"
ifconfig_vtnet0_ipv6="up"
ifconfig_vtnet0_aliases="\
  inet 192.168.0.1/24 inet6 fe80::1/64 inet6 2001:6b8::/64"

# ifconfig vtnet0
vtnet0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST>
metric 0 mtu 1500 options=80028<VLAN_MTU,JUMBO_MTU,LINKSTATE>
        ether 58:9c:fc:0b:99:97
        inet 192.168.0.1 netmask 0xffffff00 broadcast 192.168.0.255
        inet6 fe80::1%vtnet0 prefixlen 64 scopeid 0x2
        inet6 2001:6b8:: prefixlen 64
        media: Ethernet 10Gbase-T <full-duplex>
        status: active
        nd6 options=1<PERFORMNUD>

-m

-- 
Michael Gmelin