While a full IPv4 BGP table (512k day) was in excess of 512,000 prefixes, many older routers had a limit of 512k (512,000–524,288) routing table entries. On August 12, 2014, outages resulting from full tables hit eBay, LastPass and Microsoft Azure among others. A number of Cisco routers commonly in use had TCAM, a form of high-speed content-addressable memory, for storing BGP advertised routes. On impacted routers, the TCAM was by default allocated as 512k IPv4 routes and 256k IPv6 routes. While the reported number of IPv6 advertised routes was only about 20k, the number of advertised IPv4 routes reached the default limit, causing a spillover effect as routers attempted to compensate for the issue by using slow software routing (as opposed to fast hardware routing via TCAM). The main method for dealing with this issue involves operators changing the TCAM allocation to allow more IPv4 entries, by reallocating some of the TCAM reserved for IPv6 routes, which requires a reboot on most routers. The 512k problem was predicted by a number of IT professionals.
While a full IPv4 BGP table (512k day) was in excess of 512000 prefixes many older routers had a limit of 512k (512000–524288) routing table entries On August 12 2014 outages resulting from full tables hit eBay LastPass and Microsoft Azure among others A number of Cisco routers commonly in use had TCAM a form of high-speed content-addressable memory for storing BGP advertised routes On impacted routers the TCAM was by default allocated as 512k IPv4 routes and 256k IPv6 routes While the reported number of IPv6 advertised routes was only about 20k the number of advertised IPv4 routes reached the default limit causing a spillover effect as routers attempted to compensate for the issue by using slow software routing (as opposed to fast hardware routing via TCAM) The main method for dealing with this issue involves operators changing the TCAM allocation to allow more IPv4 entries by reallocating some of the TCAM reserved for IPv6 routes which requires a reboot on most routers The 512k problem was predicted by a number of IT professionals