[NBLUG/talk] Strange ethernet issue

akleider at sonic.net akleider at sonic.net
Thu Apr 12 01:47:43 PDT 2012


There seem to be two possible Debian packages to get the arping utility:
arping  and
iputils-arping

Is there any reason to get the one over the other?

alex

> FWIW, the arp query is effectively what the system does when you run
> ifup -- before it brings up the interface, it ARPs, and if it gets
> responses, it doesn't bring up the iface to avoid collisions.  So
> doing the arp might give you some idea of what the server is seeing
> that prevents it from bringing the interface up.
>
> David
>
>
> On Tue, Apr 10, 2012 at 3:20 PM, Steve Johnson <fratm at adnd.com> wrote:
>> I just don't see the point in the arp query when I am sitting in the
>> same room as all the gear and I can see what is plugged into the
>> switch.  Is there a point that I am missing?
>>
>> -Steve
>>
>>
>> On Tue, Apr 10, 2012 at 3:17 PM, Kyle Rankin <kyle at nblug.org> wrote:
>>> On Tue, Apr 10, 2012 at 09:59:46AM -0700, Steve Johnson wrote:
>>>> Yes, I physically checked the switch (Cisco switch.. not sure on
>>>> model).. Also just to be sure I ran mmap on the IP of one the boxes
>>>> when it was down and nothing came back.  I know pings are unreliable,
>>>> but nmap isn't supposed to use just IMCP, so it should have detected
>>>> something if someone got on my network.
>>>>
>>>> I will try the arp queries after tonights reboot.. These machines are
>>>> production machines, so can't be down long in the middle of the day..
>>>> :)
>>>>
>>>> -Steve
>>>
>>> Even if the machine is up, you might get interesting information from
>>> an
>>> arp query from a different host on the same subnet. Perform the arp
>>> query
>>> from a different host and confirm that you get back the MAC address you
>>> expect.
>>>
>>> -Kyle
>>>
>>>>
>>>>
>>>> On Tue, Apr 10, 2012 at 9:54 AM, Kyle Rankin <kyle at nblug.org> wrote:
>>>> > On Tue, Apr 10, 2012 at 09:40:31AM -0700, Steve Johnson wrote:
>>>> >> Hi Guys,
>>>> >>
>>>> >> I am running 3 linux boxes all on the same network, running static
>>>> 10
>>>> >> net addresses, each on their own IP address..  A strange thing has
>>>> >> started happening about a month ago, if I reboot the box when the
>>>> >> system comes up at the point when it tries to bring up the eth0
>>>> >> interface I get an error "IP Address in use by another host" and
>>>> then
>>>> >> the interface does not come up.  Loggin in from the console as root
>>>> >> and running ifup eth0 gives me the same error.  The only way I can
>>>> get
>>>> >> the interface to come up is to physically unplug the ethernet, then
>>>> >> run ifup eth0, that brings up the eth0 correctly, and then plug the
>>>> >> ethernet cable back in.. Then it runs fine until another reboot (Or
>>>> if
>>>> >> I ifdown eth0 I will have the same problem)..
>>>> >>
>>>> > <snip>
>>>> >>
>>>> >> Ay ideas, or clues would be greatly appreciated.. I've been trying
>>>> to
>>>> >> trouble shoot this for over a month now with now luck.
>>>> >>
>>>> >> -Steve
>>>> >>
>>>> >
>>>> > Are you absolutely sure that only one host truly has those IP
>>>> addresses on
>>>> > that subnet? When the host comes up and tries to assign the IP
>>>> addresses to
>>>> > itself, it will first perform an ARP and see if another MAC address
>>>> on the
>>>> > network claims to have that IP. What I would do is take down one of
>>>> the
>>>> > hosts, then from a different machine run ARP queries for those 10
>>>> IPs
>>>> > belonging to the first host and see if the MAC address you get back
>>>> is the
>>>> > correct one. If your networking guys are trying to do anything fancy
>>>> with
>>>> > NAT and misconfigured something, it could be that your switch is
>>>> claiming
>>>> > to have those IPs (it's easy to check, an arp query against one of
>>>> the IPs
>>>> > will return back a MAC belonging to a Cisco, HP, or whatever switch
>>>> you
>>>> > have).
>>>> >
>>>> > --
>>>> > Kyle Rankin
>>>> > NBLUG President
>>>> > The North Bay Linux Users' Group
>>>> > http://nblug.org
>>>> > IRC: greenfly at irc.freenode.net #nblug
>>>> > kyle at nblug.org
>>>> >
>>>
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>
> --
> David Tomaschik
> OpenPGP: 0x5DEA789B
> http://systemoverlord.com
> david at systemoverlord.com
>
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