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I'm trying to configure IPv6 on a dedicated Ubuntu server. My provider gave me a "/64" (whatever that is - I'm still confused) of IPv6 addresses.

However, when I try to use them, I can't ping anything. What do I do? :(

# ping6
    PING 56 data bytes
    From fe80::219:d1ff:fefb:42d8 icmp_seq=1 Destination unreachable: Address unreachable
    From fe80::219:d1ff:fefb:42d8 icmp_seq=2 Destination unreachable: Address unreachable
    From fe80::219:d1ff:fefb:42d8 icmp_seq=3 Destination unreachable: Address unreachable

     --- ping statistics ---
    3 packets transmitted, 0 received, +3 errors, 100% packet loss, time 2014ms

# tracepath6
    1?: [LOCALHOST]                        0.025ms pmtu 1500
    1:  fe80::219:d1ff:fefb:42d8%eth0                       2000.022ms !H
    Resume: pmtu 1500

# cat /etc/network/interfaces
    # The loopback network interface
    auto lo
    iface lo inet loopback

    # The primary network interface
    auto eth0
    iface eth0 inet static

    address 64.***.***.***
    gateway 64.***.***.***

    iface eth0 inet6 static
    pre-up modprobe ipv6
    address 2607:F878:1:***::1
    netmask 64
    gateway 2607:F878:1:***(same as address)::1

# ifconfig
    eth0      Link encap:Ethernet  HWaddr 00:19:d1:fb:42:d8
         inet addr:64.***.***.***  Bcast:64.***.***.***  Mask:
         inet6 addr: fe80::219:d1ff:fefb:42d8/64 Scope:Link
         inet6 addr: 2607:f878:1:***::1/64 Scope:Global
         RX packets:52451 errors:0 dropped:0 overruns:0 frame:0
         TX packets:39729 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:1000
         RX bytes:6817761 (6.8 MB)  TX bytes:6153835 (6.1 MB)
         Interrupt:41 Base address:0xc000

    lo        Link encap:Local Loopback
         inet addr:  Mask:
         inet6 addr: ::1/128 Scope:Host
         UP LOOPBACK RUNNING  MTU:16436  Metric:1
         RX packets:166 errors:0 dropped:0 overruns:0 frame:0
         TX packets:166 errors:0 dropped:0 overruns:0 carrier:0
         collisions:0 txqueuelen:0
         RX bytes:31714 (31.7 KB)  TX bytes:31714 (31.7 KB)
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Default Gateways work a bit differently on IPv6.

What I suggest you do is fire up tcpdump and watch it for Router Advertisements (you might want to analyse the capture in WireShark - much easier). This is how your IPv6 host knows how to get out to the internet. Also watch for Neighbor Solicitation as this is the replacement for ARP.

If you see these requests coming in, but not going back out, then your internal firewall is blocking IPv6 traffic. If you see them going out (requests), but not back in, then you need to make sure that your prefix length is correct (that's the /64 part. Although I've seen a lot of /64s being passed out that are actually a /48).

Big Important Bold Bit

ICMP is absolutally critical for IPv6 functionality. In IPv4 it can be blocked without huge impact, but in IPv6, the whole network relies on ICMP for all its functionality. Don't block it.

In reference to

My provider gave me a "/64" (whatever that is - I'm still confused) of IPv6 addresses

That's your Prefix Length, previously known as your Subnet Mask that's used for CIDR. The lower the number, the more IP addresses you have. For IPv6, /64 and /48 are very common and should give you more IP addresses than you will ever need in your entire life.

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Don't set the gateway on the host acting as the router to itself. If your ISP provided a gateway address, use that as the gateway on the host, or let the host use router announcements to configure itself. The gateway address should never be the same as the server's own address. The address being used to route for other hosts should not have a gateway assigned.

Your ISP may have provided you with an address for your external (Internet) interface. Configure your eth0 interface using that with the corresponding gateway address if it is provided. Use the /64 address on your internal interface (eth1) if you have one. You will also want to setup radvd to run on that interface.

If you don't have an internal interface you can add a static address in your /64 range by adding a line to your inet6 configuration like.

up ip -6 addr add 2607:F878:***::2 dev eth0

Get to know the ip commands such as ip -6 addr, ip -6 route, and ip -6 neigh. It is common to have multiple addresses and routes.

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