3 ms·
There's no minimum subnet size.
by megous 2y ago
There's no minimum subnet size.
- immibis 2y ago/64 acts as a soft limit due to the prevalence of SLAAC. Which is good in a way, since it means ISPs have to give out at least /64, which means you're always able to subnet (although you can't use SLAAC and must use static addresses or DHCP) unlike IPv4 where you have to pay for extra addresses.
- GoblinSlayer 2y agoThe purpose of SLAAC intends to have many customers in one /64 network though.
- immibis 2y agoNo, just many devices. You can DoS your whole subnet by pretending to be a billion devices. In IPv4 you can do it by occupying all the IP addresses. Therefore putting several customers on one network is a bad idea, just like in IPv4.
- icedchai 2y agoThe purpose of SLAAC is to make it "easy" for a client to get onto the network without something like a DHCP server tracking addresses. If you set it up, it generally just works.
- GoblinSlayer 2y agoPreviously it worked by putting the MAC address in the last 64 bits.
- icedchai 2y agoYes, that was before privacy extensions. It hasn't been like that (in most implementations) for a very long time.
- GoblinSlayer 2y agoAnd you get no privacy if /64 prefix is a stable identifier of one customer.
- icedchai 2y agoThis doesn't seem like an IPv6-specific issue. For most broadband customers, your external IPv4 address is also generally stable. Mine hasn't changed in years.
- megous 2y agoYes, you can't use SLAAC feature, but there's no subnetting limit in IPv6. Any subnet size works. Writing to you from /72.
- unethical_ban 2y agoYou're technically correct, but ISPs best practice is to hand out a /64.