A routing table limit in some BGP routers causes minor Internet outages this week. Large networks and websites suffered performance issues to outages in a series of disruptions and outages on Tuesday. The disruptions were due to a routing table issue that impacts older Internet routers. The expansion of routable networks on the Internet overwhelmed the amount of memory set aside in routers and switches, that determines the appropriate way to route data through the Internet. For the first time, the border gateway protocol (BGP) tables -surpassed a significant value (two to the 19th power or 512K). Many older routers limit their use of ternary content-addressable memory (TCAM) to 512K by default. When the routing tables outgrew the space the routers shut down or slowed. The issues appear to be isolated because only a small fraction of BGP tables have exceeded 512K entries, most routers have not been impacted by the issue. Each providers routing tables are a bit different, as what they count as a legitimate network varies, so only a small percentage of routing tables have reached the 512K limit. This could happen more over the coming weeks, as more tables hit that limit, and the network problems could multiply. The issue appears to have surprised many network engineers. Network-hardware vendors did not give much warning as to the dangers of the default configuration of older routers, and engineers likely put off resolving the issue. In May, Cisco published an advisory warning of the issue and advising customers of workarounds for the issue. Read Ciscos advisory here Experts do not believe the issue will dramatically impact Internet operations. Only older routers and switches are affected, and most can be reconfigured to assign more memory to routing IPv4 traffic, however this will come at the expense of IPv6 allocations. Hopefully this issue will help bring some attention back to the adoption of IPv6. Take advantage of our special offer to learn more about
Posted on: Fri, 15 Aug 2014 19:08:45 +0000