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2.8.2. Key Differences
Key IPv6 Differences from IPv4
| Feature | IPv4 | IPv6 |
|---|---|---|
| Address length | 32 bits | 128 bits |
| Notation | Decimal (192.168.1.1) | Hexadecimal (2001:DB8::1) |
| Broadcast | Yes | No (uses multicast instead) |
| ARP | Yes | No (uses NDP) |
| Header | Variable length, 12+ fields | Fixed 40 bytes, 8 fields |
| Fragmentation | Routers and hosts | Hosts only |
| DHCP | DHCPv4 | DHCPv6 or SLAAC |
NDP (Neighbor Discovery Protocol) does ARP's job and more with ICMPv6 messages, using multicast where IPv4 would broadcast:
| Message | Sent by | Purpose |
|---|---|---|
| Neighbor Solicitation (NS) | Any node | Ask for a neighbor's MAC address (the ARP request); also used for Duplicate Address Detection |
| Neighbor Advertisement (NA) | Any node | Answer with the MAC address (the ARP reply) |
| Router Solicitation (RS) | Host | Ask the link's routers to advertise now instead of waiting |
| Router Advertisement (RA) | Router | Announce the link's prefix and prefix length and offer the router as default gateway, which is what SLAAC builds an address from |
Resolved neighbors are cached (show ipv6 neighbors). REACH means reachability was confirmed recently. STALE means the reachable time has passed without confirmation: the entry stays in the cache and is re-checked (DELAY, then PROBE with a unicast NS) the next time traffic is sent to it. INCMP means resolution is still in progress.
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Written byAlvin Varughese
Founder•20 professional certifications