On Thu, 26 Mar 2015 18:10:59 +0100 Jen Linkova <furry13@gmail.com> wrote:
researching this topic for a customer all I found was "DO NOT DO THIS IT WILL BREAK THINGS!"
Nope it will absolutely not.
This is a very strong statement ;)
Because it is true; and verified personally by usage of ULA+GUA for years on diverse server and client devices and operating systems. Not "something I read on the Internet".
Whatever you have been reading, was written either by a somewhat misinformed person (putting it mildly), or you maye have misread/misunderstood something.
Or those people have to deal with hosts which did not implemented RFC6724 and used default address selection algorithm as it is defined in RFC3483.
Perhaps you meant https://tools.ietf.org/html/rfc3484; and even by that RFC, the "longest-matching prefix" rule 8 would prevent ULA from being selected over GUA as the outgoing address for connection to a GUA IP in case when the node has both (as in the situation we're discussing now), since fc00::/7 has zero matching leading bits with 2000::/3. -- With respect, Roman