512K Day - Internet Hiccups - You Are Not Alone

The issues with connectivities to certain computers and servers does not affect only everyday users but also major businesses, especially those primarily relying their business on the cloud servers, cloud storage, and SaaS/PaaS solutions. With the introduction of cloud computing, total number of IP addresses has grown every month ever since.

From Wiki:
512K Day is the unofficial title of an event that occurred on August 12, 2014. Multiple Internet routers, manufactured by Cisco and other vendors, encountered a default software limit of "512K" (actually 2^19) IPv4 BGP routing table entries, causing assorted outages at various data centers. Various IT professionals reported the issue on Internet forums, sometimes as just "512K", and under a Twitter hashtag of #512k.

Quote from Reddit:
BGP is the backbone of the internet and the internets just got fat enough for the backbone to start cracking.

Here's the explanation in detail from BGPMon.

What caused the instability
Folks quickly started to speculate that this might be related to a known default limitation in older Cisco routers. These routers have a default limit of 512K routing entries in their TCAM memory. The BGP routing table size depends on a number of variables. The primary contributors are Internal, or local routes (more specific and VPN routes used only in the local AS) and External routes. These External routes are all the routes of everyone on the Internet, we sometimes refer to this as the global routing table of Default Free Zone (DFZ). For most networks on the Internet today the global routing table is the major contributor, while local routes vary from a few dozen to a few hundred. Only a small percentage of the networks have a few thousand Internal routes.
The size of the global routing table today (August 12 2014) is about 500k, this number marginally varies per provider. Let’s compare a few major ISP’s. The table below shows the number of IPv4 prefixes received per provider on a full feed BGP session.
ProviderLocationNumber of IPv4 routes on full BGP feed
Level3Amsterdam497,869
GTTAmsterdam499,272
NTTAmsterdam499,610
TelstraSydney491,522
NTTSydney500,265
SingtelSingapore501,061
NTTSingapore499,830
Level3Chicago497,470
GTTChicago499,326
NTTChicago499,523
The table above shows that depending on the provider and location the numbers differ slightly, but are indeed very close. It also shows that right now the number of prefixes is still several thousands under the 512,000 limit so it shouldn’t be an issue.  However when we take a closer look at our BGP telemetry we see that starting at 07:48 UTC about 15,000 new prefixes were introduced into the global routing table.
The Internet routing table will continue to grow organically and we will reach the 512,000 limit soon again. The good news is that there’s a work-around for those operating these older cisco routers.

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