On Wednesday 15 July 2009 13:10, Javier Viguera wrote:
> Hi all,
>
> Just an issue i found when doing a little test with ping applet. Using
> current git i build busybox with only "ping" applet:
>
> busybox.git$ git rev-parse HEAD
> 0ad438b12a97159c43c9bfc75a4ae4873ecf9bf9
>
> busybox.git$ make allnoconfig
>
> busybox.git$ make menuconfig
> (select just ping applet)
>
> busybox.git$ make
>
> After compiling i make a little test with the "-I" option of ping.
> According to ping's help:
>
> "-I iface/IP Use interface or IP address as source"
>
> I have a network card in my PC with IP address 192.168.105.1.
>
> busybox.git$ ifconfig eth1
> eth1 Link encap:Ethernet HWaddr 00:0e:0c:34:11:fa
> inet addr:192.168.105.1 Bcast:192.168.255.255 Mask:255.255.0.0
> inet6 addr: fe80::20e:cff:fe34:11fa/64 Scope:Link
> UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
> RX packets:3584314 errors:0 dropped:0 overruns:0 frame:0
> TX packets:1073306 errors:0 dropped:0 overruns:0 carrier:0
> collisions:0 txqueuelen:100
> RX bytes:2660837294 (2.4 GB) TX bytes:560001009 (534.0 MB)
> Base address:0xdcc0 Memory:fe6c0000-fe6e0000
>
>
> When i try to ping the interface itself with the -I option, it only
> works if i set the IP address, but not the interface name:
>
> busybox.git$ sudo ./busybox -I eth1 192.168.105.1
> PING 192.168.105.1 (192.168.105.1): 56 data bytes
>
> --- 192.168.105.1 ping statistics ---
> 2 packets transmitted, 0 packets received, 100% packet loss
>
> busybox.git$ sudo ./busybox -I 192.168.105.1 192.168.105.1
> PING 192.168.105.1 (192.168.105.1) from 192.168.105.1: 56 data bytes
> 64 bytes from 192.168.105.1: seq=0 ttl=64 time=0.052 ms
> 64 bytes from 192.168.105.1: seq=1 ttl=64 time=0.064 ms
> 64 bytes from 192.168.105.1: seq=2 ttl=64 time=0.069 ms
>
> --- 192.168.105.1 ping statistics ---
> 3 packets transmitted, 3 packets received, 0% packet loss
> round-trip min/avg/max = 0.052/0.061/0.069 ms
>
> Is this the normal behavior? or have i hit a bug?
Yes, it's normal.
Think about it. When you ping *yourself*,
do ping packets really go over the physical wire?
Of course not. They exist only inside your computer.
In other words, they go over _loopback interface_!
Proof:
# ip a
1: lo: <LOOPBACK,UP,10000> mtu 16436 qdisc noqueue
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
link/ether 00:1d:7d:c2:ec:70 brd ff:ff:ff:ff:ff:ff
inet 10.0.0.1/24 brd 10.0.0.255 scope global if
# ./busybox ping -I eth0 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 56 data bytes
^C
--- 10.0.0.1 ping statistics ---
2 packets transmitted, 0 packets received, 100% packet loss
# ./busybox ping -I lo 10.0.0.1
PING 10.0.0.1 (10.0.0.1): 56 data bytes
64 bytes from 10.0.0.1: seq=0 ttl=64 time=0.089 ms
64 bytes from 10.0.0.1: seq=1 ttl=64 time=0.064 ms
64 bytes from 10.0.0.1: seq=2 ttl=64 time=0.065 ms
^C
--- 10.0.0.1 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max = 0.064/0.072/0.089 ms
--
vda
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