Host and Network Addressing #

A brief refresher on IPv4 #

IPv4: 32-bit addresses a.b.c.d where each quartet is 8 bits
Hard to refer to an IP space as individual IPs, so come up with CIDR: Class Interdomain Routing
- e.g. a.0.0.0/8: contains a. with any suffix
Minimum size for routing on the public internet is a /24
Address space limited by 32 bits; already ran out of IPv4 addresses
To get address: client queries DHCP server, which has a pool of addresses to give out, and returns a DHCP lease on an IP address
- Later: ask for a DHCP renewal to keep using the IP address (without renewal, timeout and IP goes back in the pool)

128-bit addresses for a larger possible address space
But also: cleaned up a bunch of other legacy artifacts from IPv4; lots of unnecessary fields gone
Addresses have two halves (so smallest assigned IP is a /64):
- Network part is always a /64, containing:
  - Registry (/23)
  - ISP prefix (/32)
  - Site prefix (/48), smallest prefix allowed to be advertised
  - Subnet prefix (/64)
- Interface ID is a /64
IPv6 has no ARP; has DHCP, but is different:
- No broadcast
- Multicast address for all local routes
- Send out router discovery request (ICMP), dest: multicast for local routers
- Router does not send back client IP; sends back a bit saying managed IP address space or unmanaged
  - Unmanaged IP case: responsible for finding own IP address
    - Pick random value (neighbor discovery request) - used in practice, as it’s easier than the other following option
    - Or: MAC addresses are supposedly unique, so use <24 bits of MAC>::fffe:<24 bits of MAC> = 64 bits
      - However, this allows tracking of a device across networks!
      - So, keep a global counter of the number of times we needed to come up with an IP address, IP suffix is: MD5(MAC || ctr++)
Numbers of hits of Google: up to 35-40% adoption of IPv6
- Mostly on mobile phones
- Mobile and cloud providers love v6!