- 2070 Bhadra · 4+6 marks
IPv6 migration; IPv4 vs IPv6 packet structure
Short answer
Migration is needed because IPv4 addresses are exhausted, NAT breaks end-to-end, routing tables are large, and IPv6 adds autoconfiguration, security, and efficiency. IPv4 routers fragment, use ARP and DHCP, and have variable 20-60 byte headers with checksum and TTL. IPv6 routers never fragment, use NDP and SLAAC, and have fixed 40-byte headers with flow label and 128-bit addresses.
Why the world has decided to migrate to new internet addressing scheme IPv6? Compare IPv4 and IPv6 router with their packet structure.
Why migrate to IPv6
- IPv4 address exhaustion: IPv4 has 2^32 (about 4.3 billion) addresses. IANA gave out its last blocks in 2011 and the RIRs followed, while billions of phones, laptops and IoT devices need addresses.
- NAT problems: NAT, the workaround, breaks end-to-end connectivity and complicates peer-to-peer apps, VoIP and security (IPsec).
- Large routing tables: poor aggregation of IPv4 blocks makes backbone routing tables huge; IPv6 is hierarchical.
- Auto-configuration: IPv4 needs DHCP or manual set-up; IPv6 hosts configure themselves.
- Security and QoS: IPsec support is built in, and the flow label supports QoS.
- Efficiency: a simpler header, no router fragmentation and no checksum speed up forwarding.
- Mobility and growth: better support for mobile devices and future services.
IPv4 router vs IPv6 router
| Basis | IPv4 router | IPv6 router |
|---|---|---|
| Header processing | Variable header, recomputes checksum, decrements TTL | Fixed header, no checksum, decrements Hop Limit |
| Fragmentation | Fragments if needed | Never fragments; sends ICMPv6 Packet Too Big |
| Address resolution | ARP | Neighbour Discovery (NDP) |
| Host configuration | DHCP | Router Advertisement (SLAAC), DHCPv6 |
| Routing protocols | RIPv2, OSPFv2, BGP-4 | RIPng, OSPFv3, MP-BGP |
| Broadcast | Forwards or blocks broadcasts | No broadcast; uses multicast |
| Table size | Large | Smaller |
Packet structure comparison
| IPv4 header | IPv6 header |
|---|---|
| 20 to 60 bytes, variable (Options field) | Fixed 40 bytes |
| Version, IHL, ToS, Total Length | Version, Traffic Class, Payload Length |
| Identification, Flags, Fragment Offset | Removed; moved to Fragment extension header |
| TTL | Hop Limit |
| Protocol | Next Header |
| Header Checksum | Removed |
| Source/Destination 32 bit | Source/Destination 128 bit |
| Options, Padding | Extension headers |
| (none) | Flow Label (new, 20 bits) |
IPv4: [Ver|IHL|ToS|Total Len]
[ID | Flags | Frag Off ]
[TTL|Proto| Checksum ]
[Source 32][Dest 32][Options]
IPv6: [Ver|TClass|Flow Label ]
[Payload Len|NextHdr|Hop]
[Source 128][Dest 128]
IPv6 has 8 fields against 12 in IPv4. Both are carried inside the link-layer frame (e.g. Ethernet type 0x0800 for IPv4 and 0x86DD for IPv6).
✓ Answer checked by Claude Opus 5.5 (high effort)
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