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BGP by Iljitsch van Beijnum

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Physical and Datalink Layer Problems

To be able to diagnose a problem, the first thing you should know is which people, systems, protocols, and destinations are affected by the problem. When a lot of people can’t reach many destinations, this will obviously be a more serious problem then when only a few people can’t reach a small number of destinations (unless these people or destinations are especially important for some reason). More importantly, this information will help you isolate the problem. Performance problems usually show in “heavy” protocols, such as FTP or multimedia applications. Internal problems tend to affect only a subset of the network; BGP problems affect all systems equally. When you know what is happening, you should ask yourself what should be happening. Sometimes a user complains about an apparent problem situation, but later it turns out this is just the way things normally are.

It’s not always immediately apparent if a problem has something to do with BGP or if there is something wrong with a lower-layer protocol or even something physical, such as a wire or a piece of equipment. BGP makes use of the physical infrastructure and lower layer protocols, so these must function properly in order for BGP to do its job.

Broken Cable or Circuit

It’s almost impossible to distinguish a cable break from equipment or power failure at the remote end. The thing to do is make contact with the router or switch at the other end to see whether it’s still functioning. If you ...

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