Currently the syntax validation for the `preferred-lifetime` and `valid-lifetime` fields in a prefix information option within the router advertisement configuration block does not allow the preferred lifetime duration to equal the valid lifetime duration. A reading of RFC 4861 § 4.6.2 states that the preferred lifetime cannot exceed the valid lifetime but does not say it cannot equate it. Attempting to set both values to be the same as below:
```
interface eth0 {
prefix ::/64 {
+ preferred-lifetime 86400
valid-lifetime 86400
}
}
```
will yield the following error on commit:
> Prefix valid-lifetime must be greater then preferred-lifetime
`radvd` exhibits correct behaviour and will accept a `radvd.conf` with preferred lifetime equal to valid lifetime, so the issue exists solely in the validation stage within VyOS.