Best practice is to use a manual /127 address for point to point addressing described here RFC2373
for EUI-64 ERFC 2373 dictates the conversion process, which has two steps. The first is to convert the 48-bit MAC address to a 64-bit value. To do this, we break the MAC address into its two 24-bit halves: the Organizationally Unique Identifier (OUI) and the NIC specific part. The 16-bit hex value 0xFFFE is then inserted between these two halves to form a 64-bit address.
I understand perfectly where you would use the /127 manual address assignment , but I cant really see the benefits in using the EUI-64. unless i am totally missing the actual purpose of this address function.
can someone kindly shed some light on the EUI-64 use cases specifically in a ISP WAN topology if possible. or point me in the direction of some reading material please.
Best Answer
This is the subject of a large debate that's been going on for a while.
When it comes down to it, using a /127 on a point-to-point link isn't really a terrible idea. RFC6164 illustrates that it actually may be a good idea to use a /127 - it identifies some of the big issues for moving to a /127 on a P2P link, and talks about the steps that have been taken to mitigate, if any. The fear of ping-pong attacks was mitigated in the most recent version of ICMP, and neighbor cache exhaustion attacks are actually eliminated on P2P links by using a /127 prefix.
EUI-64 is generally preferable on user subnets, since SLAAC generally breaks if /64 subnets are not used. On P2P links where SLAAC is not used, it's not that big of a deal.
In conclusion, I believe the general consensus is that using a /127 is not a big deal - in fact you may want to allocate a single /64 for all your P2P links. Your routing table may take a small hit since all of the P2P prefixes won't be easy to summarize, but it's unlikely to be a significant problem. Just keep the RFC I mentioned in mind, and make sure you follow the guidelines it provides.