** Description changed: Description: When the user is doing "ping -f myhostname.tld", ping does a ipaddr->hostname request at EACH packet. Which is quite a lot when used with a -f option. Moreover it is quite useless as when used with -f, ping doesnt display the result of the ipaddr->hostname, but only a single dot per packet. - I discovered this when implementing a nss plugin (/etc/nsswitch.conf kindof stuff). - I dunno the actual impact of this, just seems like very inefficient. - But if the nss plugin doesn't have an request cache, this will become quite a denial of service for this service + + -gjarboni's addition-- + + Actually, this can be a lot worse in certain cases. For example, try + pinging dnstest.bigjar.com. You can't reproduce this in text but what + happens is: + + Pinging machine sends out ICMP echo request + Pinging machine sends out in-addr.arpa DNS query (ip address -> DNS name) + Pinging machine receives NXDOMAIN (no such record) from DNS server + ------ 5 to 10 seconds pass ------ + Pinging machine prints: + 64 bytes from 12.173.97.1: icmp_seq=1 ttl=252 time=20.9 ms + + This happens for every packet. If you interrupt ping during the 5 to 10 + second period it will print the "64 bytes from ..." bit before returning + to the shell prompt. + + I shudder to imagine someone trying to walk a user through testing + connectivity with this bug. It also occurs in Debian 4.0. + + I have packet traces and a much more detailed write up if anyone is + interested. This bug doesn't happen with all IP addresses that don't + have a hostname associated with them, just certain ones, but it appears + to specific to certain name servers.
-- ping doing LOTS of useless dns request https://bugs.launchpad.net/bugs/82720 You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs