Estimate memory and entry requirements for a routing table given prefix counts.
Each entry in a router's Routing Information Base (RIB) or Forwarding Information Base (FIB) consumes a roughly fixed amount of memory to store the prefix, next-hop, metric, and associated attributes — commonly estimated at 60-80 bytes per IPv4 route depending on the platform and how much metadata is retained. Total memory demand is simply the number of routes multiplied by that per-route cost, and multiplied again by any redundancy factor for platforms that replicate the FIB across multiple forwarding engines or line cards. This is a key capacity-planning concern for internet-facing routers as the global IPv4 and IPv6 routing tables continue to grow.
Routing table memory
memory = routes × avg_bytes_per_route × redundancy_factor
The full internet default-free zone (DFZ) IPv4 routing table has grown past 900,000-1,000,000 routes and continues increasing over time, which is why older routers with limited TCAM/memory eventually need hardware upgrades or filtering policies to keep operating on the public internet.
Each RIB/FIB entry stores far more than the raw prefix: the next-hop address, outgoing interface, metric/cost, administrative distance, BGP attributes (AS path, communities, local preference) for BGP routes, and internal data structure overhead for the tree/trie used for fast lookups — all of which adds up to tens of bytes per entry beyond the prefix itself.
Distributed router architectures with multiple line cards or forwarding engines often replicate the FIB to each one so that every card can make independent, high-speed forwarding decisions without querying a central control plane for every packet — this improves forwarding performance at the cost of multiplying the total memory required across the chassis.