Hanno’s Coding Log: software development, geek stuff

redundant routes and DNS

Today one of the biggest regional internet providers in Germany experienced almost a complete loss of service (in German). Rumours go on that this had to do with a DNS problem.

No matter whether this was the real reason, it reminds me that we are heavily relying on DNS infrastructure when using internet services.

The IP layer itself with its various routing protocols offers protection against quite tremendous hardware failures on the network layer. Most bigger networks have redundant routes and a failure in a part of the network will not affect the rest.

However it is often the case that DNS servers are redundant (mirrored servers, etc.), however they might not be distributed over the network. So what if the subnetwork that contains the DNS servers goes down?

Most of the time many other services will go down as well, because DNS names are used in configurations. (Where IP addresses might have been used.)

Of course you will loose flexibility, when only using IP addresses, but whenever you rely on another service (like DNS) — think about the consequences in case of a failure.

The same goes for redundant servers behind one route. With the single cable to the subnet you have a single point of failure that can kill all your redundancy efforts.

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