Internet measurements can reveal unexpected results

Measurements always reveal new insights or unexpected results about the system under study. This applies to a wide range of systems including the Internet. Two recent scientific articles provide unexpected results about two very different protocols: ICMP and BGP.

ICMP is a network layer protocol that is used by routers to provide feedback to sources about the transmission of the packets. It is used by applications such as traceroute, ping or solutions like Path MTU Discovery defined in RFC8201. Recently, researchers in Aachen who probe the entire IPv4 addressing space to track the utilisation of specific protocols, looked at the ICMP messages that they received. As expected, they observed standard destination unreachable or port unreachable messages. In Hidden Treasures - Recycling Large-Scale Internet Measurements to Study the Internet’s Control Plane, Jan Ruth, Torsten Zimmermann, and Oliver Hohlfeld discuss a wide range of ICMP messages that they observed. If you like to dig into unexpected measurement results, I’d encourage you to have a look at this paper.

BGP is that standard interdomain routing protocol. When a BGP router announces a new prefix, the corresponding route is propagated towards all BGP routers in the public Internet. If later this router stops announcing the prefix, then the corresponding route will be removed from all other BGP routers in the public Internet. In a recent paper entitled BGP Zombies: an Analysis of Beacons Stuck Routes, Romain Fontugne and his colleagues analyse the problem of BGP zombies, routes that have been removed by their origin router but still exist in some parts of the Internet. These BGP Zombies are probably caused by some bugs in routers which could explain the fact that some routes are not totally removed. Romain also wrote an interesting blog post summarizing the key results of the paper. These are interesting sources of information to better understand the BGP protocol.

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Written on May 6, 2019