Why ping tries to resolve reverse DNS?

[Marcos]

I missed that option! thanks!

2010/8/17 James Hogarth <james.hogarth at gmail.com>

> On 17 August 2010 09:22, Marcos <fraga.muerete at gmail.com> wrote:
> > Hi everyone,
> >
> > I noticed a timeout while pinging, and as ping wasn't losing packets, I
> did
> > and strace and got the following (among many output)
> >
> >
> > # strace ping server
> >
> > [...]
> > write(5, "RESOLVE-ADDRESS 10.1.1.25\n", 26) = 26
> > read(5, "-15 Timeout reached\n", 4096)  = 20
> > close(5)                                = 0
> > munmap(0x7fc72972b000, 4096)            = 0
> > write(1, "64 bytes from 10.1.1.25: icmp_se"..., 5864 bytes from
> 10.1.1.25:
> > icmp_seq=2 ttl=125 time=0.319 ms
> > ) = 58
> > sendmsg(3, {msg_name(16)={sa_family=AF_INET, sin_port=htons(0),
> > sin_addr=inet_addr("10.1.1.25")},
> >
> msg_iov(1)=[{"\10\0,\237\304F\0\3!<jL\0\0\0\0\266\273\6\0\0\0\0\0\20\21\22\23\24\25\26\27"...,
> > 64}], msg_controllen=0, msg_flags=0}, MSG_CONFIRM) = 64
> > recvmsg(3, {msg_name(16)={sa_family=AF_INET, sin_port=htons(0),
> > sin_addr=inet_addr("10.1.1.25")},
> >
> msg_iov(1)=[{"E\0\0Tq(@\0}\1\2115\n\1\1\31\254\20L!\0\0004\237\304F\0\3!<jL"...,
> > 192}], msg_controllen=32, {cmsg_len=32, cmsg_level=SOL_SOCKET,
> > cmsg_type=0x1d /* SCM_??? */, ...}, msg_flags=0}, 0) = 84
> > open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 5
> > fstat(5, {st_mode=S_IFREG|0644, st_size=243, ...}) = 0
> > mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> =
> > 0x7fc72972b000
> > read(5, "127.0.0.1 localhost\n127.0.1.1 IN"..., 4096) = 243
> > read(5, "", 4096)                       = 0
> > close(5)                                = 0
> > munmap(0x7fc72972b000, 4096)            = 0
> > stat("/etc/resolv.conf", {st_mode=S_IFREG|0644, st_size=126, ...}) = 0
> > socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 5
> > connect(5, {sa_family=AF_INET, sin_port=htons(53),
> > sin_addr=inet_addr("10.1.1.25")}, 16) = 0
> > poll([{fd=5, events=POLLOUT}], 1, 0)    = 1 ([{fd=5, revents=POLLOUT}])
> > sendto(5,
> "\3718\1\0\0\1\0\0\0\0\0\0\00225\0011\0011\00210\7in-addr\4a"...,
> > 40, MSG_NOSIGNAL, NULL, 0) = 40
> > poll([{fd=5, events=POLLIN}], 1, 5000)  = 1 ([{fd=5, revents=POLLIN}])
> > ioctl(5, FIONREAD, [131])               = 0
> > recvfrom(5,
> > "\3718\205\203\0\1\0\0\0\1\0\0\00225\0011\0011\00210\7in-addr\4a"...,
> 1024,
> > 0, {sa_family=AF_INET, sin_port=htons(53),
> sin_addr=inet_addr("10.1.1.25")},
> > [16]) = 131
> > close(5)                                = 0
> > socket(PF_FILE, SOCK_STREAM, 0)         = 5
> > fcntl(5, F_GETFD)                       = 0
> > fcntl(5, F_SETFD, FD_CLOEXEC)           = 0
> > connect(5, {sa_family=AF_FILE, path="/var/run/avahi-daemon/socket"}, 110)
> =
> > 0
> > fcntl(5, F_GETFL)                       = 0x2 (flags O_RDWR)
> > fstat(5, {st_mode=S_IFSOCK|0777, st_size=0, ...}) = 0
> > mmap(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0)
> =
> > 0x7fc72972b000
> > lseek(5, 0, SEEK_CUR)                   = -1 ESPIPE (Illegal seek)
> > write(5, "RESOLVE-ADDRESS 10.1.1.25\n", 26) = 26
> > read(5,
> >
> >
> > So, why does ping try to resolve the inverse DNS? Is it the normal
> > behaviour? I find it quite annoying as I have to wait one DNS timeout
> with
> > every packet sent.
> > Any clues?
> >
> > Thanks in advance.
> >
> >
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> >
> >
>
> It is normal yes as on the output it tries to show a friendly hostname...
>
> If you do not want reverse DNS being done use the argument -n
>
> `man ping` will give you more details.
>
> James
>
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