On Thursday 2nd of February 2020, Tom Bird wrote: > Morning, > > Given the RFC for this is something like 20 years old now, but I > still see /30s being used by just about everyone, is there still a > good reason for this?
There are at least three major reasons that $EMPLOYER has not embraced /30 for customers. One is that CE support is sketchy. E.g. you can configure a /31 on a RouterBoard and it will simply fail to work. Instead you have to do it the pre-RFC way with a /32. This works for basic connectivity and some routing protocols work as well. If it breaks you get to keep both pieces. Another is that user education is lacking. Give a customer a /31 and they will invariably be on the phone asking how to configure it. Looking up how to configure yet another random brand CE is not a productive use of support resources. The last one is that with /30 you can use DHCP to hand out the single CE address. I have no idea whether DHCP supports /31, but I am confident that even if it does, most CEs will not handle it correctly. If a customer asks for a /31 specifically they can certainly have it. When they ask, they generally (alas, not always) know whether their CE does it correctly. Personally I would much rather see widespread support for 4rd (RFC7600) in CEs than support for /31. Or really, any other 4-over-6 standard, as long as almost every CE supports it. /Benny
