iputils: ping -I <iface>

iputils: ping -I <iface>

[Jan Synacek]

Hello,

There seems to be a bug(?) when calling ping with -I lo:

$ ping -I lo kernel.org

PING kernel.org (149.20.4.69) from 192.168.1.10 lo: 56(84) bytes of data.
^C

Note that 192.168.1.10 is my primary interface's address (em1). However, no
replies are coming back.

$ ping -I em1 kernel.org

PING kernel.org (149.20.4.69) from 192.168.1.10 em1: 56(84) bytes of data.
64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=1 ttl=42 time=202 ms
64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=2 ttl=42 time=187 ms
^C

Works as expected.

I know that binding to loopback probably doesn't make much sense, but I think
that ping should be able to cope with that.

Also, it would be nice to mention the difference between -I <ip> and -I <iface>
in the manpage.

I don't understand the problem clearly enough to write a patch.

Regards,
-- 
Jan Synacek
Software Engineer, BaseOS team Brno, Red Hat

Re: iputils: ping -I <iface>

[Ben Greear]

On 11/29/2012 06:12 AM, Jan Synacek wrote:
> Hello,
>
> There seems to be a bug(?) when calling ping with -I lo:
>
> $ ping -I lo kernel.org
>
> PING kernel.org (149.20.4.69) from 192.168.1.10 lo: 56(84) bytes of data.
> ^C
>
> Note that 192.168.1.10 is my primary interface's address (em1). However, no
> replies are coming back.
>
> $ ping -I em1 kernel.org
>
> PING kernel.org (149.20.4.69) from 192.168.1.10 em1: 56(84) bytes of data.
> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=1 ttl=42 time=202 ms
> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=2 ttl=42 time=187 ms
> ^C
>
> Works as expected.
>
> I know that binding to loopback probably doesn't make much sense, but I think
> that ping should be able to cope with that.

I think it would be wrong if ping worked as you suggest.  Binding to an
interface means use that interface as the source of your packets, and having
it bind hard helps when using systems with multiple NICs on same subnet
(or possibly, same IP).

> Also, it would be nice to mention the difference between -I <ip> and -I <iface>
> in the manpage.

In my opinion, -I <iface> should use SO_BINDTODEVICE, but at least in
older versions of ping it did not.

Thanks,
Ben

>
> I don't understand the problem clearly enough to write a patch.
>
> Regards,
>


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com

Re: iputils: ping -I <iface>

[Jan Synacek]

On 11/29/2012 08:48 PM, Ben Greear wrote:
> On 11/29/2012 06:12 AM, Jan Synacek wrote:
>> Hello,
>>
>> There seems to be a bug(?) when calling ping with -I lo:
>>
>> $ ping -I lo kernel.org
>>
>> PING kernel.org (149.20.4.69) from 192.168.1.10 lo: 56(84) bytes of data.
>> ^C
>>
>> Note that 192.168.1.10 is my primary interface's address (em1). However, no
>> replies are coming back.
>>
>> $ ping -I em1 kernel.org
>>
>> PING kernel.org (149.20.4.69) from 192.168.1.10 em1: 56(84) bytes of data.
>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=1 ttl=42 time=202 ms
>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=2 ttl=42 time=187 ms
>> ^C
>>
>> Works as expected.
>>
>> I know that binding to loopback probably doesn't make much sense, but I think
>> that ping should be able to cope with that.
> 
> I think it would be wrong if ping worked as you suggest.  Binding to an
> interface means use that interface as the source of your packets, and having
> it bind hard helps when using systems with multiple NICs on same subnet
> (or possibly, same IP).

I just wanted to point out that if I call ping with -I lo, its 'from' address is
wrong (in my case 192.168.1.10) and nothing happens (that's, I guess, expected
if it really bound to loopback). If I call ping with the -I <the same address>
or -I em1 (the same address again), it works as expected. I'm sorry if I wasn't
clear enough.

> 
>> Also, it would be nice to mention the difference between -I <ip> and -I <iface>
>> in the manpage.
> 
> In my opinion, -I <iface> should use SO_BINDTODEVICE, but at least in
> older versions of ping it did not.

Ping does use SO_BINDTODEVICE.

> 
> Thanks,
> Ben
> 

Regards,
-- 
Jan Synacek
Software Engineer, BaseOS team Brno, Red Hat

Re: iputils: ping -I <iface>

[YOSHIFUJI Hideaki]

(2012年11月30日 15:06), Jan Synacek wrote:
> On 11/29/2012 08:48 PM, Ben Greear wrote:
>> On 11/29/2012 06:12 AM, Jan Synacek wrote:
>>> Hello,
>>>
>>> There seems to be a bug(?) when calling ping with -I lo:
>>>
>>> $ ping -I lo kernel.org
>>>
>>> PING kernel.org (149.20.4.69) from 192.168.1.10 lo: 56(84) bytes of data.
>>> ^C
>>>
>>> Note that 192.168.1.10 is my primary interface's address (em1). However, no
>>> replies are coming back.
>>>
>>> $ ping -I em1 kernel.org
>>>
>>> PING kernel.org (149.20.4.69) from 192.168.1.10 em1: 56(84) bytes of data.
>>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=1 ttl=42 time=202 ms
>>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=2 ttl=42 time=187 ms
>>> ^C
>>>
>>> Works as expected.
>>>
>>> I know that binding to loopback probably doesn't make much sense, but I think
>>> that ping should be able to cope with that.
>>
>> I think it would be wrong if ping worked as you suggest.  Binding to an
>> interface means use that interface as the source of your packets, and having
>> it bind hard helps when using systems with multiple NICs on same subnet
>> (or possibly, same IP).
> 
> I just wanted to point out that if I call ping with -I lo, its 'from' address is
> wrong (in my case 192.168.1.10) and nothing happens (that's, I guess, expected
> if it really bound to loopback). If I call ping with the -I <the same address>
> or -I em1 (the same address again), it works as expected. I'm sorry if I wasn't
> clear enough.
> 
>>
>>> Also, it would be nice to mention the difference between -I <ip> and -I <iface>
>>> in the manpage.
>>
>> In my opinion, -I <iface> should use SO_BINDTODEVICE, but at least in
>> older versions of ping it did not.
> 
> Ping does use SO_BINDTODEVICE.

So far, -I device is related to source address selection (using
SO_BINDTODEVICE) and outgoing device (using in_pktinfo).
On the other hand, -I addr is, in fact, related to source
address selection (and it is enfoced by bind), only.

Something like this:

       -I interface
              interface is either an address, or an interface name.  If
              interface is an address, it sets source address to
              specified interface address.   If  interface
              in  an  interface name, it tells the command to use that
              interface.  For ping6, when doing ping to a link-local
              scope address, link specification (by the
              '%'-notation in destination, or by this option) is
              required.

BUT, even with -I device, net/ipv4/dev_inet.c:inet_select_addr()
may select an address from other interfaces, AFAIK).

Should we check if the selected source address blongs to the actual
device?

--yoshfuji

Re: iputils: ping -I <iface>

[Ben Greear]

On 11/30/2012 11:04 AM, YOSHIFUJI Hideaki wrote:
> (2012年11月30日 15:06), Jan Synacek wrote:
>> On 11/29/2012 08:48 PM, Ben Greear wrote:
>>> On 11/29/2012 06:12 AM, Jan Synacek wrote:
>>>> Hello,
>>>>
>>>> There seems to be a bug(?) when calling ping with -I lo:
>>>>
>>>> $ ping -I lo kernel.org
>>>>
>>>> PING kernel.org (149.20.4.69) from 192.168.1.10 lo: 56(84) bytes of data.
>>>> ^C
>>>>
>>>> Note that 192.168.1.10 is my primary interface's address (em1). However, no
>>>> replies are coming back.
>>>>
>>>> $ ping -I em1 kernel.org
>>>>
>>>> PING kernel.org (149.20.4.69) from 192.168.1.10 em1: 56(84) bytes of data.
>>>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=1 ttl=42 time=202 ms
>>>> 64 bytes from pub2.kernel.org (149.20.4.69): icmp_seq=2 ttl=42 time=187 ms
>>>> ^C
>>>>
>>>> Works as expected.
>>>>
>>>> I know that binding to loopback probably doesn't make much sense, but I think
>>>> that ping should be able to cope with that.
>>>
>>> I think it would be wrong if ping worked as you suggest.  Binding to an
>>> interface means use that interface as the source of your packets, and having
>>> it bind hard helps when using systems with multiple NICs on same subnet
>>> (or possibly, same IP).
>>
>> I just wanted to point out that if I call ping with -I lo, its 'from' address is
>> wrong (in my case 192.168.1.10) and nothing happens (that's, I guess, expected
>> if it really bound to loopback). If I call ping with the -I <the same address>
>> or -I em1 (the same address again), it works as expected. I'm sorry if I wasn't
>> clear enough.
>>
>>>
>>>> Also, it would be nice to mention the difference between -I <ip> and -I <iface>
>>>> in the manpage.
>>>
>>> In my opinion, -I <iface> should use SO_BINDTODEVICE, but at least in
>>> older versions of ping it did not.
>>
>> Ping does use SO_BINDTODEVICE.
>
> So far, -I device is related to source address selection (using
> SO_BINDTODEVICE) and outgoing device (using in_pktinfo).
> On the other hand, -I addr is, in fact, related to source
> address selection (and it is enfoced by bind), only.
>
> Something like this:
>
>         -I interface
>                interface is either an address, or an interface name.  If
>                interface is an address, it sets source address to
>                specified interface address.   If  interface
>                in  an  interface name, it tells the command to use that
>                interface.  For ping6, when doing ping to a link-local
>                scope address, link specification (by the
>                '%'-notation in destination, or by this option) is
>                required.
>
> BUT, even with -I device, net/ipv4/dev_inet.c:inet_select_addr()
> may select an address from other interfaces, AFAIK).
>
> Should we check if the selected source address blongs to the actual
> device?

Maybe have -D <iface-name> and -P <source-address>
options?

Where -D uses SO_BINDTODEVICE, and -P binds to a source IP?

Would have to keep the -I logic similar to what it does now for
backwards compatibility...

Thanks,
Ben

>
> --yoshfuji
>


-- 
Ben Greear <greearb@candelatech.com>
Candela Technologies Inc  http://www.candelatech.com