I'm running Ubuntu 16.04 behind a router. I can get IPv6 on the router working, but it fails on the client. If anyone has any input on how I can resolve that, I'd appreciate it.

I can use either SLAAC (radvdump output, below) or DHCPv6 to get an IP from the ISP, resulting in an IP based on the MAC of the router's WAN interface, plus a link-local. ip -6 addr on the router shows:

inet6 2607:X:X:X:Y:yff:fey:Y/64 scope global dynamic

Then, I can set the router's LAN interface to static: 2607:X:X:X::/64 and use the routers's stateless or stateful DHCP server to get addresses for the client (first address only present when using the stateful server):

inet6 2607:X:X:X::x/128         scope global dynamic
inet6 2607:X:X:X:Y':Y':Y':Y'/64 scope global temporary dynamic 
inet6 2607:X:X:X:Z:Z:Z:Z/64     scope global mngtmpaddr noprefixroute dynamic

ip -6 route on the client (first route only present when using the stateful server and fe80::Y:yff:fey:Y is the link-local ip of the router's LAN interface)

2607:X:X:X::x dev enp0s25 proto kernel metric 256 expires 86292sec pref medium 
2607:X:X:X::/64 via fe80::Y:yff:fey:Y dev enp0s25 proto ra metric 100 pref medium
2607:X:X:X::/64 dev enp0s25 proto kernel metric 256 expires 7090sec pref medium
fe80::/64 dev enp0s25 proto kernel metric 256 pref medium
default via fe80::Y:yff:fey:Y dev enp0s25 proto static metric 100 pref medium

When the router is set to use DHCP with the ISP, I can also try to dispense with the static setting for the router's LAN interface, by using prefix delegation; but then whether I use stateful or stateless DHCP with the client, I only get a link-local address. This seems odd as the prefix/netmask are included in the ISP's router advertisement (below).


# radvdump [run on the router]

interface ath0
    AdvSendAdvert on;
    # Note: {Min,Max}RtrAdvInterval cannot be obtained with radvdump
    AdvManagedFlag off;
    AdvOtherConfigFlag on;
    AdvReachableTime 0;
    AdvRetransTimer 0;
    AdvCurHopLimit 64;
    AdvDefaultLifetime 1800;
    AdvHomeAgentFlag off;
    AdvDefaultPreference medium;
    AdvSourceLLAddress on;

    RDNSS 2607:X:X:X::53
        AdvRDNSSPreference 0;
        AdvRDNSSOpen off;
        AdvRDNSSLifetime 1800;
    }; # End of RDNSS definition

    prefix 2607:X:Y:Y::/64
        AdvValidLifetime 2592000;
        AdvPreferredLifetime 604800;
        AdvOnLink on;
        AdvAutonomous on;
        AdvRouterAddr off;
    }; # End of prefix definition

}; # End of interface definition
# radvd configuration generated by radvdump 1.2
# based on Router Advertisement from fe80::Z:Z:Z:Z
# received by interface ath0

/etc/network/interfaces is unchanged from the ubuntu install:

auto lo
iface lo inet loopback

I also note here the output of sysctl. This answer indicates I may need to change some of these, but others indicate that changes should be in the interfaces file and/or Network Manager, and that these don't play well with sysctl. It's the enp0s25 interface that connects to the LAN:

$ sudo sysctl -a | grep accept_ra

net.ipv6.conf.all.accept_ra = 1
net.ipv6.conf.all.accept_ra_defrtr = 1
net.ipv6.conf.all.accept_ra_from_local = 0
net.ipv6.conf.all.accept_ra_min_hop_limit = 1
net.ipv6.conf.all.accept_ra_mtu = 1
net.ipv6.conf.all.accept_ra_pinfo = 1
net.ipv6.conf.all.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.all.accept_ra_rtr_pref = 1
net.ipv6.conf.default.accept_ra = 1
net.ipv6.conf.default.accept_ra_defrtr = 1
net.ipv6.conf.default.accept_ra_from_local = 0
net.ipv6.conf.default.accept_ra_min_hop_limit = 1
net.ipv6.conf.default.accept_ra_mtu = 1
net.ipv6.conf.default.accept_ra_pinfo = 1
net.ipv6.conf.default.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.default.accept_ra_rtr_pref = 1
net.ipv6.conf.enp0s25.accept_ra = 1
net.ipv6.conf.enp0s25.accept_ra_defrtr = 0
net.ipv6.conf.enp0s25.accept_ra_from_local = 0
net.ipv6.conf.enp0s25.accept_ra_min_hop_limit = 1
net.ipv6.conf.enp0s25.accept_ra_mtu = 1
net.ipv6.conf.enp0s25.accept_ra_pinfo = 0
net.ipv6.conf.enp0s25.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.enp0s25.accept_ra_rtr_pref = 0
net.ipv6.conf.lo.accept_ra = 1
net.ipv6.conf.lo.accept_ra_defrtr = 1
net.ipv6.conf.lo.accept_ra_from_local = 0
net.ipv6.conf.lo.accept_ra_min_hop_limit = 1
net.ipv6.conf.lo.accept_ra_mtu = 1
net.ipv6.conf.lo.accept_ra_pinfo = 1
net.ipv6.conf.lo.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.lo.accept_ra_rtr_pref = 1
net.ipv6.conf.virbr0.accept_ra = 0
net.ipv6.conf.virbr0.accept_ra_defrtr = 1
net.ipv6.conf.virbr0.accept_ra_from_local = 0
net.ipv6.conf.virbr0.accept_ra_min_hop_limit = 1
net.ipv6.conf.virbr0.accept_ra_mtu = 1
net.ipv6.conf.virbr0.accept_ra_pinfo = 1
net.ipv6.conf.virbr0.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.virbr0.accept_ra_rtr_pref = 1
net.ipv6.conf.virbr0-nic.accept_ra = 1
net.ipv6.conf.virbr0-nic.accept_ra_defrtr = 1
net.ipv6.conf.virbr0-nic.accept_ra_from_local = 0
net.ipv6.conf.virbr0-nic.accept_ra_min_hop_limit = 1
net.ipv6.conf.virbr0-nic.accept_ra_mtu = 1
net.ipv6.conf.virbr0-nic.accept_ra_pinfo = 1
net.ipv6.conf.virbr0-nic.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.virbr0-nic.accept_ra_rtr_pref = 1
net.ipv6.conf.wlp3s0.accept_ra = 0
net.ipv6.conf.wlp3s0.accept_ra_defrtr = 0
net.ipv6.conf.wlp3s0.accept_ra_from_local = 0
net.ipv6.conf.wlp3s0.accept_ra_min_hop_limit = 1
net.ipv6.conf.wlp3s0.accept_ra_mtu = 1
net.ipv6.conf.wlp3s0.accept_ra_pinfo = 0
net.ipv6.conf.wlp3s0.accept_ra_rt_info_max_plen = 0
net.ipv6.conf.wlp3s0.accept_ra_rtr_pref = 0
  • Looks like you configured the same prefix on WAN and LAN sides of the router. That's incorrect. Your ISP need to route a prefix to your WAN address such that you can use that on the LAN. How to get a routed prefix depends on the ISP. Some require your router to request a prefix through DHCPv6. I have come across one that have a website where you can get a routed prefix. – kasperd Oct 29 at 13:28
  • Thanks @kasperd. It does appear there is no PD with DHCP, as far as I can make out - though I'd like to be 100% sure. I'll either have to go for a bridge - in which case I need to figure out how to assign myself non-mac based IPv6's - or run an IPv6 NAT, which I'll also have to figure out how to do. The project exhausted me though, so I'm going to get back to it in a bit.... – Diagon Oct 30 at 2:04
  • Both of those approaches are absolutely inferior. A routed prefix is the way to go. If your router requests a delegated prefix and you don't get a routed prefix that way, you need to ask your ISP how to get a routed prefix. – kasperd Oct 30 at 8:05
  • While I agree, this is an unsupported university visitor network. So I'm on my own. I'll try to find out how to do a packet capture & make sure there's no prefix advertised, but otherwise those are the choices. – Diagon Oct 30 at 8:24

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