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the_nuts
Asked: 2017-07-18 23:26:53 +0800 CST

Adding a /64 ipv6 block, only the first one works [duplicate]

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I have a Ubuntu 16.04.2 server with a /64 block of IPv6s.

If I add the block, like this:

ip addr add 2001:41d0:xxx:yyy::/64 dev eth2

only the first one works:

$ curl -g http://[2001:41d0:xxx:yyy::]/
<!DOCTYPE html>...
$ curl -g http://[2001:41d0:xxx:yyy::1]/
curl: (7) Failed to connect to 2001:41d0:xxx:yyy::1 port 80: Connection timed out

If I add the others one by one, they work:

ip addr add 2001:41d0:xxx:yyy::1/128 dev eth2

What I am doing wrong?

The block is also in /etc/network/interfaces:

iface eth2 inet6 static
    address 2001:41d0:xxx:yyy::
    netmask 64
networking

2 Answers

  1. Best Answer

    An interface address is a single address, although you can assign a bunch of IPv6 addresses to an interface, so you are really adding the 2001:41d0:xxx:yyy:: address in the 2001:41d0:xxx:yyy::/64 network to an interface.

    IPv6 actually allows you to use every address in a network for a host address, unlike IPv4 where the network address cannot be used as a host address, but RFC 2373, IP Version 6 Addressing Architecture defines the Router-Subnet anycast address as the all-zeroes address for a network.

    2.6.1 Required Anycast Address

    The Subnet-Router anycast address is predefined. Its format is as follows:

    |                         n bits                 |   128-n bits   |
+------------------------------------------------+----------------+
|                   subnet prefix                | 00000000000000 |
+------------------------------------------------+----------------+

    The "subnet prefix" in an anycast address is the prefix which identifies a specific link. This anycast address is syntactically the same as a unicast address for an interface on the link with the interface identifier set to zero.

    Packets sent to the Subnet-Router anycast address will be delivered to one router on the subnet. All routers are required to support the Subnet-Router anycast addresses for the subnets which they have interfaces.

    • 4

  2. @Ron_Maupin gives a correct answer but I felt it would be complimented by a simpler one:

    /64 doesn't imply the whole block is assigned to the interface. It assigned one address to the interface and tells it that the LAN has the /64 block. This is almost always what you want for an Ethernet interface.

    /128 is almost never what you want for an Ethernet interface. These addresses will not be reachable from the LAN.

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