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How frequently do routing tables change in core-network routers? Once every 30sec? once every minute? every 5minutes?

I know that there is a Border Gateway Protocol that runs in the core Internet routers and learns about optimal network paths between adjacent routers, I am just wondering about the frequency of the routing table updates.

If, for example, a Youtube video starts streaming to my PC, what is the chance that the route taken by the packets - which start their journey, in theory, from some Google server, and end up after 15-20 hops to my PC - changes DURING the time I am watching the 10min video? Is it fair to say, that in most cases, the intermediate routers stay the same for a period of 10min? What is the probability of this not being the case? 5%? 20% ?

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2 Answers 2

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The frequency of changes really depends where in the network you are.

There is a project to track and visualize BGP change in the internet: BGPlay; between that and BGPmon/RouteViews, you can get a lot more data.

I grabbed the data for yesterday (2013/12/06) from BGPmon: there were 11976 updates in total. As to answering if your route to a google server changed, even the data directly wouldn't tell you that (if neither endpoint moved, you wouldn't see it in the data). Instead you'd have to have continuously traceroute the PC/Google route, and watch that for changes, then map that back to data seen by BGPMon or RouteViews.

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From Cisco documentation "BGP neighbors exchange full routing information when the TCP connection between neighbors is first established. When changes to the routing table are detected, the BGP routers send to their neighbors only those routes that have changed. BGP routers do not send periodic routing updates, and BGP routing updates advertise only the optimal path to a destination network. "

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