Routing in IPv6 is essentially the same process as routing in IPv4 under CIDR (Classless Inter-Domain Routing), with the main difference being the address length. Instead of using 32-bit IPv4 addresses, IPv6 uses 128-bit addresses. This means that IPv6 routing involves directing network traffic based on these longer addresses to ensure data reaches its intended destination.
Key Aspects of IPv6 Routing
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Address Structure: The core difference between IPv4 and IPv6 routing lies in the address format. IPv6's 128-bit addresses allow for a massive increase in the available address space, which leads to very large routing tables.
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Routing Algorithms: The underlying routing protocols and algorithms that are used in IPv4 routing, such as OSPF (Open Shortest Path First), RIP (Routing Information Protocol), IDRP (Inter-Domain Routing Protocol), and IS-IS (Intermediate System to Intermediate System), can be adapted with simple modifications to support IPv6.
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CIDR: Like IPv4, IPv6 routing extensively uses CIDR for efficient address allocation and summarization, ensuring the routing tables remain manageable.
How IPv6 Routing Works
- Destination Lookup: When an IPv6 packet is received by a router, the router examines the destination IPv6 address.
- Route Selection: The router uses its routing table, which maps prefixes of destination IPv6 addresses to interfaces or the next hop router, to select the optimal path to forward the packet.
- Packet Forwarding: The packet is then forwarded out of the appropriate interface to the next hop, continuing this process until the packet reaches its destination.
Example
Imagine a packet needs to go from a device in Network A (with a source IPv6 address of 2001:db8:1::1/64) to a device in Network C (with a destination IPv6 address of 2001:db8:3::1/64).
- The packet first reaches the router in Network A.
- This router's routing table has information on how to reach different networks.
- It finds a route to Network C via Router B (perhaps a specific route to 2001:db8:3::/64).
- The packet is sent to Router B, which then repeats the process, eventually forwarding the packet to its intended destination on Network C.
Similarities to IPv4 Routing
- Both utilize routing protocols to learn network topologies and determine the best paths.
- Both employ the concept of next-hop routing.
- Both are based on IP addressing and subnetting using CIDR.
Differences from IPv4 Routing
- Address Size: 128-bit versus 32-bit addresses, which changes the way they're stored and processed within routers.
- Address Space: IPv6 provides a much larger address space, thus eliminating the need for NAT (Network Address Translation) for public address space conservation.
Conclusion
In summary, IPv6 routing mirrors IPv4 routing in principle, operating under CIDR and utilizing similar routing algorithms. The critical difference lies in the expanded address space of IPv6, requiring adjustments to address handling within the routing process.
