IPV6 : Configuring For RedHat

The following works on Redhat 8.0. It should be almost identical in Redhat 7.3. Take a look at the docmentation in /usr/share/doc/initscripts-6.95 for more details.
In /etc/sysconfig/network we enable IPv6 support and support for the 6to4 tunnelling by adding the following lines:

NETWORKING_IPV6=yes
IPV6_DEFAULTDEV=tun6to4

In /etc/sysconfig/network-scripts/ifcfg-{devname} we need to enable IPv6. This device will be the device on which the tunnel IPv6 traffic travels over. So this could be a ppp device or an eth device. NOTE: I do not think ippp device (ISDN) are supported at the moment. We enable IPv6 be adding:

IPV6INIT=yes
IPV6TO4INIT=yes
IPV6TO4_RELAY="192.88.99.1"

Additional steps for ppp devicesIf the 6to4 device is a ppp device then extra configuration is needed
In /etc/ppp/ip-up.local a call to the IPv6 configuration scripts needs to be added:

/etc/ppp/ip-up.ipv6to4 $1

In /etc/ppp/ip-down.local a call to the IPv6 configuration scripts needs to be added:

/etc/ppp/ip-down.ipv6to4 $1

And finally if the local IP address of the device is not configured in the ifcfg-ppp{unit} file then you need to ensure that the real linux device always matches the {unit} number. I fyou only have one ppp device then this will be true as the device will always be called ppp0. If you have more than one device then I recomend renaming it to something with a higher unit number (5 for example) and the forcing it to use that unit number by adding the following to /etc/sysconfig/network-scripts/ifcfg-{devname}

PPPOPTIONS="unit {unit}"

for ppp devices, or

PPPD_EXTRA="unit {unit}"

for pppoe devices.