A device that joins a network needs an address, a gateway and a resolver. DHCP and IPv6 neighbour discovery are how that happens.
DHCP: the DORA exchange
- Discover — client broadcasts: is there a DHCP server?
- Offer — server offers an address and settings.
- Request — client requests the offer.
- Acknowledge — server confirms the lease.
The lease includes an IP, subnet mask, gateway, DNS servers and duration.
A rogue DHCP server can hand out a malicious gateway or DNS server. DHCP snooping and port security reduce the risk.
IPv6 basics
- 128-bit addresses, written in hex.
- A typical LAN is a
/64, leaving 64 bits for the interface identifier. - SLAAC lets a host build an address from a router-advertised prefix.
- NDP handles address resolution, router discovery and reachability.
A /64 contains an enormous number of addresses, so scanning is impractical. Discovery and monitoring rely on router advertisements, neighbour tables and flow data.
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