PSA: Global IPv4 Routing Table Hits 500k Routes

Last week, the global IPv4 routing table has surpassed the 500 thousand route benchmark, according to the CIDR Report. The graph below shows its progression since the early nineties:

I last wrote about global IPv4 growth in August of 2009, when the table size was at a mere 300 thousand routes. While that benchmark was largely ceremonial, this one crosses a threshold which should may be of grave concern for many.

As has been pointed out on the NANOG mailing list, we are quickly approaching the hard forwarding plane capacity limits which exists on several very popular platforms, namely the Cisco 7600/6500 and RSP720/Sup720. The default TCAM partitioning scheme of these platforms allows for a maximum of 512 thousand IPv4 routes.

If you accept full Internet routes anywhere on your network, you'll want to verify the maximum table sizes for those platforms. On the 6500/7600 platform, the current partitioning scheme can be inspected with show mls cef maximum-routes:

Router# show mls cef maximum-routes
FIB TCAM maximum routes :
=======================
Current :
---------
 IPv4 + MPLS         - 512k (default)
 IPv6 + IP Multicast - 256k (default)

The good news is that it's easy to repartition the default scheme (e.g. mls cef maximum-routes ip 768) to allow for more IPv4 space. Unfortunately, this requires taking the device out of production for a time to be rebooted.

Thanks to @nixgeek and the NANOG folks for inspiring this post!