De : Mikael Abrahamsson <swmike@swm.pp.se> A : Mark Andrews <marka@isc.org>,
You can hand out /48 as easily with 6rd as you can natively.
"As easily". It's easier to either hand out /64 by means of 1:1 mapping IPv4 and IPv6, or (if ability exists) hand out /48 or /56 using PD, than
to get into the whole backend mess of having multiple 6RD domains with multiple configs per IPv4 subnet etc.
I agree with you theoretically, but in practice I disagree.
Some hard data points here, coming from one of the rare operator who actually deployed 6RD sub-domains to all its customers (to my knowledge). In practice, most 6RD implementations that support option 212 do support IPv4MaskLen properly these days. It wasn't the case 3 years ago, but we worked a lot with vendors to make it right. Seems ok now, we mostly have a 6RD population of D-Link and Cisco/Linksys. On the backend side, it's really not that bad. A one-page TCL handles around 15-16 sub-domains for us without noticeable impact on the DHCP servers CPU. Configuring the relays with all the tunnels can be a bit of fun playing with hex maths, but it's not too bad either. So I agree with Mark, it's not that complex. I can't agree with him on the prefix size though. We hand out /60s because we feel it's enough from a transition point of view (these are short-lived anyway) and offering a bigger size would really use too much space. Offering /48s out of a single /16 block, to take a simple example, would use a whole /32. This space wouldn't be used much anyway, given that most 6RD routers use only one /64, sometimes two. I argue that a /60 is actually the best compromise here, from a space and usage point of view. /JF Videotron, AS5769