netdev - Re: Ping Is Broken

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Message-ID: <7e84ed60910121214n71413383v3ee703ea6042f355@mail.gmail.com>
Date:	Mon, 12 Oct 2009 14:14:13 -0500
From:	Rob Townley <rob.townley@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	CentOS mailing list 
	<public-centos-IFYaIzF+flcdnm+yROfE0A@...ne.gmane.org>,
	public-netdev-u79uwXL29TY76Z2rM5mHXA@...ne.gmane.org,
	Omaha Linux User Group 
	<public-olug-u8lKhlSLHjY@...ne.gmane.org>
Subject: Re: Ping Is Broken




On Mon, Oct 12, 2009 at 4:47 AM, Jarek Poplawski <jarkao2@...il.com> wrote:
>
>
> On 09-10-2009 18:44, Rob Townley wrote:
>> ping -I is broken
>>
>> The following deals with bug in ping that made it very difficult to set up a
>> system with two gateways.
>>
>> Demonstration that *ping -I is broken*. When specifying the source
>> interface using -I with an *ethX* alias and that interface is not the
>> default gateway
>> interface, then ping fails. When specifying the interface as an ip address,
>> ping works. Search for "Destination Host Unreachable" to find the bug.
>>
>>
>> eth*0* = 4.3.2.8 and the default gateway is accessed through a different
>> interface eth*1*.
>> eth*1* = 192.168.168.155 is used as the device to get to the default
>> gateway.
>> *FAILS *: ping *-I eth0* 208.67.222.222
>> *WORKS*: ping *-I 4.3.2.8* 208.67.222.222
>> *WORKS*: ping *-I eth1* 208.67.222.222
>> *WORKS*: ping *-I 192.168.168.155* 208.67.222.222
> ...
>> man ping:
>>    -I interface address
>>         Set source address to specified interface address.
>>         Argument may be *numeric IP address or name of device*.
>>         When  pinging  IPv6  link-local  address  this option is required.
>
> It seems this description might be misleading that IP address and name
> of device are equivalent here, while they are treated a bit different.
> The device name is additionally used in a sendmsg message, probably to
> guarantee the device is really used (not its address only), so it
> looks like intended.
>
>> ping -V returns the latest available on CentOS and Fedora and the
>> maintainers website:
>> ping utility, iputils-ss020927
>
> I guess the patch below could do what you expect in this case, but
> rather "man" should be fixed...

Thank you for the patch.  i will test it. i was trying to find the
problem using gdb and figure out a patch myself.

ping used to work the way i expected many many years ago on various
*nix systems.
Besides, traceroute is broken by the same problem except that
traceroute is much more explicit with a -i and -s parameters.  Who
knows what else is broken by all the meddling in interface name
aliases without testing.

MultiNic / MultiGatewayed machines are hard enough in Linux, lets not
give users a reason to use BSD or Windows.

>
> Jarek P.
> ---
>
> --- ping.c.orig 2002-09-20 15:08:11.000000000 +0000
> +++ ping.c      2009-10-12 08:51:25.000000000 +0000
> @@ -323,7 +323,7 @@ main(int argc, char **argv)
>                perror("ping: icmp open socket");
>                exit(2);
>        }
> -
> +#if 0
>        if (device) {
>                struct ifreq ifr;
>
> @@ -336,7 +336,7 @@ main(int argc, char **argv)
>                cmsg.ipi.ipi_ifindex = ifr.ifr_ifindex;
>                cmsg_len = sizeof(cmsg);
>        }
> -
> +#endif
>        if (broadcast_pings || IN_MULTICAST(ntohl(whereto.sin_addr.s_addr))) {
>                if (uid) {
>                        if (interval < 1000) {
>
> --
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