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What is IPv6 Link-Local Router Address?

Published in IPv6 Networking 3 mins read

An IPv6 link-local router address is a specific type of IPv6 address that routers use for communication within a single network link. It's designed to allow devices on the same local network segment to communicate without requiring globally unique addresses or configuration from a central authority like a DHCP server.

Here's a breakdown:

  • Purpose: Facilitates communication between neighboring IPv6 devices (including routers) on the same network segment, without routing beyond that segment. It's used for tasks like router discovery, neighbor discovery, and autoconfiguration.

  • Scope: Link-local addresses are not routable beyond the local network link. Routers will not forward packets with a source or destination address that is a link-local address.

  • Address Format: All IPv6 link-local addresses begin with the prefix fe80::/10. This means they always start with fe80, fe81, fe82, or fe83. The remaining 54 bits of the address are typically derived from the device's interface identifier (often based on its MAC address). This guarantees uniqueness within the local network.

  • Automatic Configuration: Every IPv6-enabled interface automatically configures a link-local address. This happens regardless of whether the interface also has a global unicast address or not. This allows for immediate communication on the local network.

  • Interface Specification: Because link-local addresses are only unique within a single network link, when using a link-local address, you must specify the interface you are sending the traffic out of. For example, you might see ping fe80::201:4f:5f:6f%eth0, where eth0 is the interface. This tells the system which physical network to send the ping to.

  • Router Advertisement: Routers use link-local addresses to send Router Advertisement (RA) messages. These messages allow hosts on the network to autoconfigure their IPv6 addresses, learn about the network prefix, and find the default router.

Key Characteristics:

  • Non-routable: Packets with link-local source or destination addresses are not forwarded by routers.
  • Automatic: Every IPv6-enabled interface automatically configures one.
  • Prefix: fe80::/10
  • Interface-specific: Requires the interface to be specified when used.
  • Used for: Neighbor discovery, router advertisements, and local communication.

Example:

A typical IPv6 link-local address for a router might look like fe80::200:0:4157:ad09. However, to actually use this address, you would need to specify the interface it belongs to, such as fe80::200:0:4157:ad09%eth0.

In summary, IPv6 link-local router addresses provide a mechanism for devices on the same network segment to communicate without relying on globally unique addresses, enabling essential network functions such as router discovery and address autoconfiguration.

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