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Networking Fundamentals · Intermediate

Global Routing Prefix

The leading portion of an IPv6 global unicast address assigned by an ISP or RIR to identify a site.

Definition

Sites commonly receive a /48 or /56 from their provider, though residential customers may receive a /60 or /64. The bits between the global routing prefix and the /64 boundary form the subnet ID. Hierarchical assignment allows aggressive route aggregation.

Example

An ISP assigns 2001:db8:acad::/48 to a company.

Exam tip

With a /48 site prefix, 16 subnet bits give 65,536 /64 subnets.

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