[gentoo-user] Machine doesn't respond to broadcast ping.

[gentoo-user] Machine doesn't respond to broadcast ping.

[Stroller]

Hi there,

I've got one machine here on the LAN which isn't responding to  
broadcast ping. Any idea why not?

$ ping -c 2 192.168.1.255
PING 192.168.1.255 (192.168.1.255): 56 data bytes
64 bytes from 192.168.1.71: icmp_seq=0 ttl=64 time=0.221 ms
64 bytes from 192.168.1.43: icmp_seq=0 ttl=64 time=0.301 ms (DUP!)
64 bytes from 192.168.1.22: icmp_seq=0 ttl=64 time=0.405 ms (DUP!)
64 bytes from 192.168.1.255: icmp_seq=0 ttl=255 time=0.649 ms (DUP!)
64 bytes from 192.168.1.9: icmp_seq=0 ttl=60 time=1.646 ms (DUP!)
64 bytes from 192.168.1.71: icmp_seq=1 ttl=64 time=0.159 ms

--- 192.168.1.255 ping statistics ---
2 packets transmitted, 2 packets received, +4 duplicates, 0% packet loss
round-trip min/avg/max/stddev = 0.159/0.564/1.646/0.509 ms
$ ping -c 3 192.168.1.100
PING 192.168.1.100 (192.168.1.100): 56 data bytes
64 bytes from 192.168.1.100: icmp_seq=0 ttl=64 time=0.297 ms
64 bytes from 192.168.1.100: icmp_seq=1 ttl=64 time=0.270 ms
64 bytes from 192.168.1.100: icmp_seq=2 ttl=64 time=0.272 ms

--- 192.168.1.100 ping statistics ---
3 packets transmitted, 3 packets received, 0% packet loss
round-trip min/avg/max/stddev = 0.270/0.280/0.297/0.012 ms
$


It's a fairly recent (last 6 months or so) Gentoo build, and is  
updated fairly regularly (every month or so).

I'd list package versions & stuff, but I have no idea which apply - I  
thought that ping was a part of the basic TCP/IP stack. Would it help  
if I posted the kernel .config? Is there an option in there to disable  
broadcast ping responses?

This isn't very important, but it does pique my curiosity. There are  
many on here more knowledgeable than I, so perhaps someone will  
quickly identify the cause?

Stroller.

Re: [gentoo-user] Machine doesn't respond to broadcast ping.

[Eray Aslan]

On 25.06.2009 07:34, Stroller wrote:
> I've got one machine here on the LAN which isn't responding to broadcast
> ping. Any idea why not?

You need to set icmp_echo_ignore_broadcasts to 0.  Default is 1, mainly
for dos prevention:

# sysctl net.ipv4.icmp_echo_ignore_broadcasts=0

-- 
Eray

RE: [gentoo-user] Machine doesn't respond to broadcast ping.

[Adam Carter]

> > I've got one machine here on the LAN which isn't responding to broadcast
> > ping. Any idea why not?
>
> You need to set icmp_echo_ignore_broadcasts to 0.  Default is
> 1, mainly for dos prevention:
>
> # sysctl net.ipv4.icmp_echo_ignore_broadcasts=0

I thought it would default to off in most OSes these days, because of;
http://en.wikipedia.org/wiki/Smurf_attack

Are those other machines patched up?

Re: [gentoo-user] Machine doesn't respond to broadcast ping.

[Stroller]

On 25 Jun 2009, at 08:10, Adam Carter wrote:

>>> I've got one machine here on the LAN which isn't responding to  
>>> broadcast
>>> ping. Any idea why not?
>>
>> You need to set icmp_echo_ignore_broadcasts to 0.  Default is
>> 1, mainly for dos prevention:
>>
>> # sysctl net.ipv4.icmp_echo_ignore_broadcasts=0
>
> I thought it would default to off in most OSes these days, because of;
> http://en.wikipedia.org/wiki/Smurf_attack
>
> Are those other machines patched up?

They're all on the LAN, anyway, but:

192.168.1.71 - the machine from which the ping was sent (don't know if  
that makes a difference). Mac OS X 10.5, fairly recent updates, but  
perhaps not this month's.
192.168.1.43 - Gentoo 1.4 profile, 2.4 kernel, not updated in at least  
3 years, well due for retirement, just as soon as I've moved services  
to 192.168.1.100
192.168.1.22 - network KVM [1], probably can't get a firmware update,  
unfortunately. :( Not a very recent one, anyway. Although they may  
still sell it, I'm pretty sure it's rebadged OEM & development on the  
product is ceased.
192.168.1.9 - LaserJet 4000, JetDirect card.

Interestingly the router is a model at least 5 years old - a Draytek  
Vigor, older than the 192.168.1.43 build - and it isn't replying.

I now realise that 3 other Linux boxes are missing from the list. I'm  
sure I'm not the only person on the list to occasionally lose count.

Anyway, for each device it's either a case of:
- yes, it's regularly updated;
- sorry, there's not much to be done about it; or
- yes, I know it needs updating!

It shouldn't matter, anyway, if they're all behind a NAT router,  
should it? I'm inclined to disable this ignore, because I do find  
broadcast ping very occasionally useful.

Stroller.



[1] http://www.austin-hughes.co.uk/products.cfm?Product=28

RE: [gentoo-user] Machine doesn't respond to broadcast ping.

[Adam Carter]

> It shouldn't matter, anyway, if they're all behind a NAT router,
> should it?

Correct. Since a broadcast ping from the Internet cant make it to your network, you're fine.

Surprised about MacOSX tho...