IPv6 Neighbor Discovery

RA messages are sent with ICMPv6. These can carry options, so they’ve been extended to carry RDNSS information.

The router can say “Here is the DNS info”.

Terms

ND — Neighbor Discoery

RA — Router Advertisement

In v6, routers can just advertise the prefix of the attached subnet and options like RDNSS.

RDNSS — Recursive DNS Server

DAD — Duplicate Address Detection

Functions

• SLAAC
• DAD
• Prefix Discoery
• Parameter Discovery
• Address Resolution
• Router Discovery
• Next-Hop Determination
• Neighbor Unreachability Detection
• Redirects

RDNS server option

RFC 8106: IPv6 Router Advertisement Options for DNS Configuration

 0                   1                   2                   3   
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
┌───────────────┬───────────────┬───────────────────────────────┐
│     Type      │     Length    │           Reserved            │
├───────────────┴───────────────┴───────────────────────────────┤
│                           Lifetime                            │
├───────────────────────────────────────────────────────────────┤
│                      Addresses of IPv6                        │
│                    Recursive DNS Servers                      │
└───────────────────────────────────────────────────────────────┘

References

RFC 4861: Neighbor Discovery for IP version 6 (IPv6) | RFC Editor

RFC 8106: IPv6 Router Advertisement Options for DNS Configuration | RFC Editor