Global internet outages caused by routing table spike

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Global internet outages caused by routing table spike

Network routers hit capacity limits.

Internet connectivity issues this week which saw many sites become unreachable were caused by a sudden spike in announcements of traffic routes between networks, which in turn pushed core routers over their default limits.

The problem started after the global routing table, which is used by internet providers to direct traffic between networks, grew suddenly with around 15,000 new prefix entries being introduced for a few minutes, making the table bigger than some core internet routers were able to handle.

By default, older core routers currently in use by providers can only store 512,000 route entries. At present, the global routing table for the internet has just under 500,000 entries, and it continues to grow as more IPv4 and IPv6 network prefixes are introduced.

According to BGPMon, the 15,000 route announcements originated mainly from US telco Verizon's autonymous systems 701 and 705.

Geoff Huston, chief scientist at the Asia-Pacific Network Information Centre (APNIC), told iTnews that core routers use very expensive and complex ternary content addressable memory (TCAM) to operate at a high packet throughput rate when looking up to which network traffic should be sent.

"Router vendors don't over provision [TCAM] more than 'necessary' as this makes their products more expensive or reduces their margins on the product. So they tend to build equipment with around three to five years of anticipated growth," Huston said.

The TCAM in today's routers is typically one to two megabytes in size, and fit both the global IPv4 and newer IPv6 routing tables.

"If you have three to five year old equipment, you may well need a TCAM transplant to cope with today's forwarding information base [routing table] size," Huston said.

A spokesperson for Brocade confirmed the limit was an issue, noting that the models with the 512,000 route default are "all but obsolete and no longer being supported."

The spokesperson said Brocade's new routers support two million routes.

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