Configure Unique Local IPv6 Addresses on RHEL 7

Configure IPv6 addresses and perform some basic IPv6 troubleshooting.

IPv6 in Brief

IPv6 Address Format

The IPv6 address is noted as 8 groups of 16 bits (which equals 4 hexadecimal numbers), for example:


There are a couple of formatting rules: leading zeroes do not have to be written, and long strings of all zeroes can be summarised as ::. This would make the previous example look like:


Common IPv6 Addresses

The localhost address is ::1/128, which is in IPv4 format.

All addresses would be ::, what is in IPv4 format.

Multicast address is ff00::/8.

Unique Local Addresses

A unique local address is an IPv6 address in the block fc00::/7. Unique local addresses are not routable in the global IPv6 Internet.

A comparison to IPv4 would be the or the addresses.

Link-local Addresses

The link-local address is automatically configured on each IPv6 interface, but does not allow for globally unique addressing.

To conform to standard /64 addressing on subnets, the actual link-local addresses are assigned with the prefix fe80::/64.

IPv6 requires a link-local address on every network interface on which the IPv6 protocol is enabled, even when routable addresses are also assigned

Configure IPv6

Add IPv6 Address to an Existing Interface

# nmcli c
NAME     UUID                                  TYPE            DEVICE
slave2   684ab2dc-6b40-4a50-b2b4-0450f65c4cef  802-3-ethernet  enp0s8
slave1   00a5d6e6-5360-414e-8997-025fdec6d09e  802-3-ethernet  enp0s17
mybond0  d021371e-5e22-4b1a-a4eb-0b96bde80702  bond            mybond0

We want to add an IPv6 address fc00::10:8:8:71 to the mybond0 interface:

# nmcli c mod mybond0 ipv6.addresses fc00::10:8:8:71/7 ipv6.method manual
# nmcli c down mybond0; nmcli c up slave1; nmcli c up slave2
# ip ad show mybond0
7: mybond0: <BROADCAST,MULTICAST,MASTER,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP
    link/ether 08:00:27:ff:71:00 brd ff:ff:ff:ff:ff:ff
    inet brd scope global mybond0
       valid_lft forever preferred_lft forever
    inet6 fc00::10:8:8:71/7 scope global
       valid_lft forever preferred_lft forever
    inet6 fe80::a00:27ff:feff:7100/64 scope link
       valid_lft forever preferred_lft forever

We see that the link-local address (scope link) is created automatically based on the network prefix fe80::/64, followed by the MAC address 08:00:27:ff:71:00 of the network card, where fffe is inserted in the middle of the MAC address part.

The unique local address (scope global) is the one that we just set up, fc00::10:8:8:71/7. We should be able to ping6 it.

# ping6 -c2 fc00::10:8:8:71
PING fc00::10:8:8:71(fc00::10:8:8:71) 56 data bytes
64 bytes from fc00::10:8:8:71: icmp_seq=1 ttl=64 time=0.037 ms
64 bytes from fc00::10:8:8:71: icmp_seq=2 ttl=64 time=0.054 ms

--- fc00::10:8:8:71 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.037/0.045/0.054/0.010 ms

The link-local addresses that can be reached through interface mybond0:

# ping6 -c2 fe80::a00:27ff:feff:7100%mybond0
PING fe80::a00:27ff:feff:7100%mybond0(fe80::a00:27ff:feff:7100) 56 data bytes
64 bytes from fe80::a00:27ff:feff:7100: icmp_seq=1 ttl=64 time=0.039 ms
64 bytes from fe80::a00:27ff:feff:7100: icmp_seq=2 ttl=64 time=0.059 ms

--- fe80::a00:27ff:feff:7100%mybond0 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.039/0.049/0.059/0.010 ms

Create a New Interface with IPv6 Address

Add a new eth2 interface and assign IPv4 and IPv6 addresses:

# nmcli c add type ethernet ifname eth2 con-name eth2 \
 ip4 gw4 \
 ip6 fc00::10:8:8:90/7 gw6 fc00::10:8:8:2

We can then modify assignments later (use ipv4.gateway if on RHEL 7.2):

# nmcli c mod eth2 ipv4.addresses "" ipv4.method manual \
 ipv6.addresses "fc00::10:8:8:91/7" ipv6.method manual

Troubleshooting IPv6

Ping all nodes (multicast address) on the local network connected to the mybond0 interface:

# ping6 ff02::1%mybond0

Check IPv6 routing table:

# ip -6 ro|grep -v error
fc00::/7 dev mybond0  proto kernel  metric 256
fe80::/64 dev mybond0  proto kernel  metric 256

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