Large number of DNS queries

asked 2011-04-19 03:47:49 -0500

updated 2014-01-28 17:09:33 -0500

ngrennan
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So there was a situation on our campus network with a computer talking to a networked ROS core that generated 9,172,713 DNS queries over a few hours. The machine that issued the requests was NOT the roscore. Is this normal or is something likely configured incorrectly?

I've only run on private wifi routers, so I've never had IT report extreme DNS usage. :)

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Sure sounds like a lot. I just ran rviz on my desktop (connected to my robot's machine which ran roscore and most of the nodes), and it executed < 1 query a minute (which could have well been other stuff on the machine).

Murph ( 2011-04-19 05:13:02 -0500 )edit

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answered 2011-04-19 05:47:58 -0500

kwc
12244 ●54 ●90 ●132 http://kwc.org/

It's unusual, but without more details about what was running on the computer, it's not easy to understand the problem. DNS queries should only result when:

a node initializes
a service call is issued

Also, monitoring scripts, like rxgraph, will do much more frequent queries as they do not maintain persistent connections to the nodes they are monitoring.

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Looks like the problem was a service call (calling a forward kinematics solver) at 100Hz. Assuming the server doesn't change, using a http://www.ros.org/wiki/roscpp/Overview/Services#Persistent_Connections should reduce the number of DNS queries, right?

Eric Perko ( 2011-04-20 13:48:00 -0500 )edit

Yes, regardless of DNS query issues, a service call at 100Hz should use a persistent connection instead. That is really high rate for a service call.

kwc ( 2011-04-20 14:40:24 -0500 )edit

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answered 2011-04-22 09:46:24 -0500

Tõnu Samuel

161 ●8 ●10 ●22 http://phippi.jes.ee/

Don't know about ROS but in any network client (Linux, Windows, router) DNS stuff is cached. Such traffic can appear only if this cache is broken somehow or queries never get cache hits because they are nearly random. You need to run some network sniffer to see if queries are same and repeating or something else. Then probably someone here can figure out what is going on.

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