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hosts getting IPv6 via DHCPv6 and hosts configured with fixed IPv6

Started by Walter H., August 21, 2022, 06:13:32 AM

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Walter H.


my routing box is just a ZBOX with a general purpose linux - a CentOS

with the tunnel I get a /64 and optional a /48

let's say the /48 is:  2001:db8:1::/48

now what I have/did ...

the NIC on LAN side of the routing box has  2001:db8:1::1 with a prefix length of 48
and fe80::1 as a secondary scope:link IPv6

as I share the LAN with my room mate and I told him, that he can use this:   2001:db8:1:2000::/64
and all his Windows machines (physical and virtual) have addresses within this prefix and a configured prefix length of 48

I myself use this:  2001:db8:1:1::/64 and also a configured prefix length of 48

the default gateway either coming by RADVd or for fixed IPv6 configuration is always fe80::1

there I have a few linux servers virtualized:

a Mail server         2001:db8:1:1::10
a DNS server         2001:db8:1:1::1
and a proxy server 2001:db8:1:1::20

they all have 48 as prefix len configured on their virtual NIC

the ISC DHCP I configured with this:


ddns-updates off;
update-static-leases true;
allow leasequery;


default-lease-time 7200;
max-lease-time 86400;

dhcpv6-lease-file-name "/var/lib/dhcpd/dhcpd6.leases";

subnet6 2001:db8:1::/48 {
        range6 2001:db8:1:7fff:0:0:0:0 2001:db8:1:7fff:ffff:ffff:ffff:ffff;
        range6 2001:db8:1:7fff::/64 temporary;

        option dhcp6.name-servers 2001:db8:1::1, 2001:db8:1:1::1;
        option dhcp6.domain-search "example.com";

        option dhcp6.info-refresh-time 600;
        option dhcp6.preference 255;

the /etc/radvd.conf looks this simple:

interface br0
        AdvSendAdvert on;

        # stateful DHCPv6: on
        # stateless DHCPv6 (SLAAC): off
        AdvManagedFlag on;

        # get DNS from DHCPd6: on
        # get DNS from RADVd: off
        AdvOtherConfigFlag on;

        MinRtrAdvInterval 5;
        MaxRtrAdvInterval 15;

        route fe80::1/64
                AdvRouteLifetime infinity;
                AdvRoutePreference high;

on the routing box the br0 device is a bridge between
the LAN device eth0 and the WLAN device wlan0

connections from any host configured with a fixed IPv6 to the 4 mentioned servers is no problem;
but from hosts getting their IPv6 from DHCPv6 this times out and no connection possible;
native connection to the internet is no problem;

just for a testing purpose I changed the configured prefix len of 48 to 64 at the mail server;
then it is possible for DHCPv6 configured clients to connect, but when I do a ping on the mail server to such a host
this looks like:

# ping6 2001:db8:1:7fff:2008:2dc9:82ed:1d14
PING 2001:db8:1:7fff:2008:2dc9:82ed:1d14 56 data bytes.
64 bytes from 2001:db8:1:7fff:2008:2dc9:82ed:1d14: icmp_seq=1 ttl=128 time=0.541 ms
64 bytes from 2001:db8:1:7fff:2008:2dc9:82ed:1d14: icmp_seq=1 ttl=128 time=0.541 ms (DUP!)
64 bytes from 2001:db8:1:7fff:2008:2dc9:82ed:1d14: icmp_seq=2 ttl=128 time=0.540 ms
64 bytes from 2001:db8:1:7fff:2008:2dc9:82ed:1d14: icmp_seq=2 ttl=128 time=0.540 ms (DUP!)

where did I made some mistake?

the goal should be the following:

the router box should have 1 IPv6 address as it has now, and I guess this must be configured with prefix len 48
and IPv6 addresses of several /64 prefixes are used independent;

please tell me what I should/must do different;



None of your subnets should have a /48, you need to subnet the /48 into /64s and use those

Walter H.

can you please tell a little bit more details ...

e.g. the workstation of my mate should use an IPv6 from 2001:db8:1:2000::/64
and for my workstation I want to use an IPv6 from 2001:db8:1:1::/64

which IPv6 addresses must be configured on the routing box?
and can any host use this default gateway fe80::1 as they are all inside the same LAN?