« 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.

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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.

Note that the timestamps of the introduction of these new prefixes overlap with the reports of hiccups on the Internet today. The picture below shows the number of prefixes received by a Level3 customer in Chicago and shows how the prefix count peaked at around 8am UTC to 515,000 prefixes and then dropped back to 500,000 prefixes. Clearly visible as well is that the 15,000 new prefixes were only visible for a few minutes.

Now that we know that there was indeed an increase in prefixes it is time to look into where these prefixes came from.  Looking at the our data we quickly see that the new prefixes being announced at that time were almost all originated by the Verizon Autonomous systems 701 and 705.  All of the new routing entries appear to be more specific announcements for their larger aggregate blocks.  For example BGPmon detected 170 more specific /24 routes for the larger 72.69.0.0/16 block.

So whatever happened internally at Verizon caused aggregation for these prefixes to fail which resulted in the introduction of thousands of new /24 routes into the global routing table.  This caused the routing table to temporarily reach 515,000 prefixes and that caused issues for older Cisco routers. »

La doc Cisco est intéressante pour comprendre la répartition dans la TCAM : http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/117712-problemsolution-cat6500-00.html. L'exemple est foireux par contre :  1000k d'IPv4 unicast donc tu fais croire aux gens qu'ils sont laaaaaarges mais donc il reste 8k pour les labels MPLS et 8k pour v4 multicast + IPv6. Le nombre de préfixes v6 c'est 18k+ déjà à l'heure actuelle ... déporter le problème v4 sur v6 : check :')