iftop-users May 2022

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[Iftop-users] iftop resolving IPs as local hostname instead of regular public PTR
by Hoggins! 25 May '22

25 May '22

Hi there, First time posting here, I'm having questions/issues regarding DNS PTR resolution when running iftop. I'm asking this because "it used to work" and now it's not outputting what I expect, and I'd like to understand why and how to circumvent the problem. I'm aware that my issue might very well be system-related, but I'm sure discussing this with you will enable me finding the culprit. Here's the thing: I have dynamic (public) IPs attached to a system (using Keepalived, everything works fine), and I monitor the traffic going on this public interface with iftop. These public IPs all have correct PTR records. eg.with dig : ;; ANSWER SECTION: 50.52.196.5.in-addr.arpa. 86369 IN PTR www.radiom.fr. But when I use iftop to monitor this public interface, all I get as resolved hostname is my local hostname. It *used* to work, and I'm pretty sure it's due to a system upgrade, maybe a library that doesn't behave as I expect it to. I checked my /etc/hosts file, but there are no entries linking public IPs and the local hostname. So my question is: where should I look to get the correct info? Is iftop using something like gethostbyaddr() to get the hostname? Thanks! Hoggins!

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iftop-users May 2022