RHCE-EX300-Configure IPv6 addresses and perform basic IPv6 troubleshooting

1. IPV6 Address text representation

Different from IPV4, IPV6 uses Hex format to represent. An IPv6 address is split into 8 elements each of which is 16 bits represented by 4 Hex number. 

XXXX : XXXX : XXXX : XXXX : XXXX : XXXX : XXXX : XXXX

EXAMPLE:

FC00:0000:0000:005A:00BB:0000:0000: 9C44

For each element, the leading 0 can be omitted. So the above address can be rewritten as below.

FC00:   0:   0:  5A:  BB:   0:   0: 9C44

Furthermore,  the first group of consecutive "0" elements can be omitted. So the above address can be rewritten as below.

FC00:         :  5A:  BB:   0:   0: 9C44

Be careful here, as only the first group of  0 elements can be omitted. If all zero groups are omitted, it will not be distinguishable.

FC00:         :  5A:  BB:         : 9C44

Another useful expression of IPV6 address is to let the last 32 bits represented as IPV4.

FC00::5A:BB:0:0.0.156.68

Actually, the above method is mostly used to translate an IPv4 to IPv6. e.g.

192.168.0.1 ----> ::192.168.0.1 --->::C0A1:1

2. Specail IPV6 addresses

2.1 Private address

FC00::/7 is used as private addresses which are not routed by internet routers, similar to IPV4's 192.168.0.0/16

2.2 Link-local address

FE80::/10 is used as link-local addresses similar to IPV4's 169.254.0.0/16

2.3 loop address

::1 is used as a loop address similar to IPv4's 127.0.0.1

3. IPV6 commands

• ping6 or "ping -6"
• ip -6
• ss -6
• mmcli to configure IPv6 address

4.  Configure IPV6 address via "nmcli"

nmcli connection modify eth0 ipv6.addresses "::192.168.100.236/64"

nmcli connection modify eth0 ipv6.method manual

nmcli connection down eth0

nmcli connection up eth0

ip -6 a

ping6 ::192.168.100.236

4.Useful links

• RFC5952, https://tools.ietf.org/html/rfc5952